Category Archives: Solar and Stellar Astrophysics

A search for stellar siblings of the ~ 200 Myr TOI-251b planetary system [SSA]

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http://arxiv.org/abs/2305.03255


Young planets (< 1 Gyr) are helpful for studying the physical processes occurring at the early stage of planet evolution. TOI-251 b is a recently discovered sub-Neptune orbiting a young G dwarf, which has an imprecise age estimation of 40-320 Myr. We select TOI-251 sibling candidates based on kinematics and spatial proximity to TOI-251, and further use the color-magnitude diagram (CMD) to refine the list and to compare to multiple open clusters. We report stellar rotational period for 321 sibling candidates in a 50 pc radius around TOI-251 by analyzing their stellar light curves, and find a color – rotational period sequence that lie in between the Group X (300 Myr) and Pleiades (120 Myr) members, suggesting an age ~ 200 Myr. A quantitative age analysis by using gyrochronology relations give 204 $\pm$ 45 Myr, consistent with the average Li-age of selected siblings (238 $\pm$ 38 Myr) and the Gaia variability age (193$^{102}_{-54}$ Myr). The detection fraction of comoving candidates that have short rotational period is 68.1%, much higher than the typical value in the field (14% – 16% from Kepler). The overdensity of young stars and consistency in age of stellar siblings suggest a potential young association candidate in the Pheonix-Grus constellation. Though TOI-251 b has a radius larger than most of its field-age counterparts, we are uncertain whether TOI-251 is inflated due to a lack of knowledge on the planet’s mass.

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Q. Sun, S. Wang, A. Mann, et. al.
Mon, 8 May 23
27/63

Comments: 19 pages, 9 figures, 3 tables, ApJ accepted

Complete replacement of magnetic flux in a flux rope during a coronal mass ejection [SSA]

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http://arxiv.org/abs/2305.03217


Solar coronal mass ejections are the most energetic events in the Solar System. In their standard formation model, a magnetic flux rope builds up into a coronal mass ejection through magnetic reconnection that continually converts overlying, untwisted magnetic flux into twisted flux enveloping the pre-existing rope. However, only a minority of coronal mass ejections carry a coherent magnetic flux rope as their core structure, which casts doubt on the universality of this orderly wrapping process. Here we provide observational evidence of a different formation and eruption mechanism of a magnetic flux rope from an S-shaped thread, where its magnetic flux is fully replaced via flare reconnections. One of the footpoints of the sigmoidal feature slipped and expanded during the formation, and then moved to a completely new place, associated with the highly dynamical evolution of flare ribbons and a twofold increase in magnetic flux through the footpoint, during the eruption. Such a configuration is not predicted by standard formation models or numerical simulations and highlights the three-dimensional nature of magnetic reconnections between the flux rope and the surrounding magnetic field.

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T. Gou, R. Liu, A. Veronig, et. al.
Mon, 8 May 23
38/63

Comments: N/A

Influence of the Lower Atmosphere on Wave Heating and Evaporation in Solar Coronal Loops [SSA]

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http://arxiv.org/abs/2305.03621


We model a coronal loop as a three-dimensional magnetic cylinder in a realistic solar atmosphere that extends from the chromosphere to the corona. Kink oscillations, believed ubiquitous in the solar corona, are launched in the loop. Heating is expected due to the dissipation of wave energy at small structures that develop from the Kelvin-Helmholtz instability induced by kink oscillations. Increases in temperature and internal energy can be observed in the coronal counterpart of the driven loop. With the presence of thermal conduction, chromospheric evaporation can also be seen. Although the volume averaged temperature and density changes seem slight ($\sim4\%$ relative to a non-driven loop), the enthalpy flow from the lower atmosphere redistributes the density and temperature in the vertical direction, thus enhancing the dissipation of wave energy in the corona. The efficient heating in the coronal counterpart of the loop can complement the thermal conductive losses shown in the current model and thus maintain the internal energy in the corona.

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M. Guo, T. Duckenfield, T. Doorsselaere, et. al.
Mon, 8 May 23
48/63

Comments: Accepted for publication in ApJL

ATOMIUM: Probing the inner wind of evolved O-rich stars with new, highly excited H$_2$O and OH lines [SSA]

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http://arxiv.org/abs/2305.03171


Water and the hydroxyl radical are major constituents of the envelope of O-rich late-type stars. Transitions involving energy levels that are highly excited have been observed in both H$2$O and OH. These and more recently discovered transitions can now be observed at a high sensitivity and angular resolution with the ALMA Array. Spectra and maps of H$_2$O and OH observed with an angular resolution of 20 to $\sim$200 mas were obtained at two epochs with the ALMA array. Observations with the Compact Array were also used to check for time variability of water transitions. Radiative transfer models of water were revisited to characterize masing conditions and up-to-date chemical models were used for comparison with our observations. Ten rotational transitions of H$_2$O with energies up to 9000 K were observed in various vibrational states. All but one are new detections in space, and from these we have derived accurate rest frequencies. Hyperfine split $\Lambda$-doubling transitions in v = 0, J = 27/2 and 29/2 levels of the $^2\Pi{3/2}$ state and, $J = 33/2$ and 35/2 of the $^2\Pi_{1/2}$ state of OH with excitation energies up to 8900 K were also observed. Four of these transitions are new detections in space. Combining our measurements with earlier observations of OH, the v = 0 and v = 1 $\Lambda$-doubling frequencies have been improved. Our H$_2$O maps show compact emission and extensions up to twelve stellar radii or more. The 268.149 GHz emission line of water in the v$_2$ = 2 state is time variable, tends to be masing with dominant radiative pumping, and is widely excited. The widespread but weaker 262.898 GHz water line in v$_2$ = 1 also shows signs of maser emission. Emission and absorption of both H$_2$O and OH reveal an infall of matter and complex kinematics influenced by binarity. From our observed column densities, we derived OH/H$_2$O abundance ratios in a few stars.

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A. Baudry, K. Wong, S. Etoka, et. al.
Mon, 8 May 23
51/63

Comments: 41 pages with references and 25 figures in main text. 4 Tables in Appendix A. 10 figures in Appendix B. 2 figures in Appendix C. 14 figures in Appendix D. 5 figures in Appendix E. 2 figures in Appendix F

Large-Scale Ejecta of Z CMa — Proper Motion Study and New Features Discovered [SSA]

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http://arxiv.org/abs/2305.03080


Z Canis Majoris is a fascinating early-type binary with a Herbig Be primary and a FU Orionis-type secondary. Both of the stars exhibit sub-arcsecond jet-like ejecta. In addition, the primary is associated with the extended jet as well as with the large-scale outflow. In this study, we investigate further the nature of the large-scale outflow, which has not been studied since its discovery almost three and a half decades ago. We present proper motion measurements of individual features of the large-scale outflow and determine their kinematical ages. Furthermore, with our newly acquired deep images, we have discovered additional faint arc-shaped features that can be associated with the central binary.

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T. Liimets, M. Kraus, L. Cidale, et. al.
Mon, 8 May 23
55/63

Comments: 15 pages, 4 figures, published in Galaxies

The surprising evolution of the shadow on the TW Hya disk [SSA]

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http://arxiv.org/abs/2305.03611


We report new total intensity visible light high contrast imaging of the TW Hya disk taken with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST). This represents the first published images of the disk with STIS since 2016, when a moving shadow on the disk surface was reported. We continue to see the shadow moving in a counter-clockwise fashion, but in these new images the shadow has evolved into two separate shadows, implying a change in behavior for the occulting structure. Based on radiative transfer models of optically thick disk structures casting shadows, we infer that a plausible explanation for the change is that there are now two misaligned components of the inner disk. The first of these disks is located between 5-6au with an inclination of 5.5\arcdeg and PA of 170\arcdeg, the second between 6-7au with and inclination of 7\arcdeg and PA of 50\arcdeg. Finally, we speculate on the implications of the new shadow structure and determine that additional observations are needed to disentangle the nature of TW Hya’s inner disk architecture.

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J. Debes, R. Nealon, R. Alexander, et. al.
Mon, 8 May 23
58/63

Comments: 20 pages, 9 figures, published in ApJ

Small-scale dynamos: From idealized models to solar and stellar applications [SSA]

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http://arxiv.org/abs/2305.02787


In this article we review small-scale dynamo processes that are responsible for magnetic field generation on scales comparable to and smaller than the energy carrying scales of turbulence. We provide a review of critical observation of quiet Sun magnetism, which have provided strong support for the operation of a small-scale dynamo in the solar photosphere and convection zone. After a review of basic concepts we focus on numerical studies of kinematic growth and non-linear saturation in idealized setups, with special emphasis on the role of the magnetic Prandtl number for dynamo onset and saturation. Moving towards astrophysical applications we review convective dynamo setups that focus on the deep convection zone and the photospheres of solar-like stars. We review the critical ingredients for stellar convection setups and discuss their application to the Sun and solar-like stars including comparison against available observations.

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M. Rempel, T. Bhatia, L. Rubio, et. al.
Fri, 5 May 23
11/67

Comments: 54 pages, 10 figures, submitted to Space Science Reviews

Predicting Stellar Rotation Periods Using XGBoost [SSA]

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http://arxiv.org/abs/2305.02407


This work aims to develop a computationally inexpensive approach, based on machine learning techniques, to accurately predict thousands of stellar rotation periods. The innovation in our approach is the use of the XGBoost algorithm to predict the rotation periods of Kepler targets by means of regression analysis. Therefore, we focused on building a robust supervised machine learning model to predict surface stellar rotation periods from structured data sets built from the Kepler catalogue of K and M stars. We analysed the set of independent variables extracted from Kepler light curves and investigated the relationships between them and the ground truth. Using the extreme gradient boosting method, we obtained a minimal set of variables that can be used to build machine learning models for predicting stellar rotation periods. Our models are validated by predicting the rotation periods of about 2900 stars. The results are compatible with those obtained by classical techniques and comparable to those obtained by other recent machine learning approaches, with the advantage of using much fewer predictors. Restricting the analysis to stars with rotation periods of less than 45 days, our models are on average 95 to 98 % correct. We have developed an innovative approach, based on a machine learning method, to accurately fit the rotation periods of stars. Based on the results of this study, we conclude that the best models generated by the proposed methodology are competitive with the state-of-the-art approaches, with the advantage of being computationally cheaper, easy to train, and relying on small sets of predictors.

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N. Gomes, F. Sordo and L. Torgo
Fri, 5 May 23
18/67

Comments: Paper submitted to A&A. Comments are welcome!

On the propagation of gravity waves in the lower solar atmosphere in different magnetic configurations [SSA]

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http://arxiv.org/abs/2305.02740


Gravity waves are generated by turbulent subsurface convection overshooting or penetrating locally into a stably stratified medium. While propagating energy upwards, their characteristic negative phase shift over height is a well-recognized observational signature. Since their first detailed observational detection and estimates of energy content, a number of studies have explored their propagation characteristics and interaction with magnetic fields and other wave modes in the solar atmosphere. Here, we present a study of the atmospheric gravity wave dispersion diagrams utilizing intensity observations that cover photospheric to chromospheric heights over different magnetic configurations of quiet-Sun (magnetic network regions), a plage, and a sunspot as well as velocity observations within the photospheric layer over a quiet and a sunspot region. In order to investigate the propagation characteristics, we construct two-height intensity – intensity and velocity-velocity cross-spectra and study phase and coherence signals in the wavenumber-frequency dispersion diagrams and their association with background magnetic fields. We find signatures of association between magnetic fields and much reduced coherence and phase shifts over height from intensity-intensity and velocity-velocity phase and coherence diagrams, both indicating suppression/scattering of gravity waves by the magnetic fields. Our results are consistent with the earlier numerical simulations, which indicate that gravity waves are suppressed or scattered and reflected back into the lower solar atmosphere in the presence of magnetic fields.

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H. Kumar, B. Kumar and S. Rajaguru
Fri, 5 May 23
20/67

Comments: 19 pages, 19 Figures, Accepted for publication in Advances in Space Research journal

Variability of Young Stellar Objects in the Perseus Molecular Cloud [SSA]

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http://arxiv.org/abs/2305.02514


We present an analysis of 288 young stellar objects (YSOs) in the Perseus Molecular Cloud that have well defined $g$ and $r$-band lightcurves from the Zwicky Transient Facility. Of the 288 YSOs, 238 sources (83% of our working sample) are identified as variables based on the normalized peak-to-peak variability metric, with variability fraction of 92% for stars with disks and 77% for the diskless populations. These variables are classified into different categories using the quasiperiodicity ($Q$) and flux asymmetry ($M$) metrics. Fifty-three variables are classified as strictly periodic objects that are well phased and can be attributed to spot modulated stellar rotation. We also identify 22 bursters and 25 dippers, which can be attributed to accretion burst and variable extinction, respectively. YSOs with disks tend to have asymmetric and non-repeatable lightcurves, while the YSOs without disks tend to have (quasi)periodic lightcurves. The periodic variables have the steepest change in $g$ versus $g-r$, while bursters have much flatter changes than dippers in $g$ versus $g-r$. Periodic and quasiperiodic variables display the lowest variability amplitude. Simple models suggest that the variability amplitudes of periodic variables correspond to changes of the spot coverage of 30% to 40%, burster variables are attributed to accretion luminosity changes in the range of $L_{\rm acc}/L_{\star}=0.1-0.3$, and dippers are due to variable extinction with $A_{V}$ changes in the range of $0.5-1.3\;$mag.

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X. Wang, M. Fang, G. Herczeg, et. al.
Fri, 5 May 23
27/67

Comments: 26 pages, 16 figures, 3 tables, accepted for publication in RAA

Carbon dredge-up required to explain the Gaia white dwarf colour-magnitude bifurcation [SSA]

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http://arxiv.org/abs/2305.02827


The Gaia colour-magnitude diagram reveals a striking separation between hydrogen-atmosphere white dwarfs and their helium-atmosphere counterparts throughout a significant portion of the white dwarf cooling track. However, pure-helium atmospheres have Gaia magnitudes that are too close to the pure-hydrogen case to explain this bifurcation. To reproduce the observed split in the cooling sequence, it has been shown that trace amounts of hydrogen and/or metals must be present in the helium-dominated atmospheres of hydrogen-deficient white dwarfs. Yet, a complete explanation of the Gaia bifurcation that takes into account known constraints on the spectral evolution of white dwarfs has thus far not been proposed. In this work, we attempt to provide such a holistic explanation by performing population synthesis simulations coupled with state-of-the-art model atmospheres and evolutionary calculations that account for element transport in the envelopes of white dwarfs. By relying on empirically grounded assumptions, these simulations successfully reproduce the bifurcation. We show that the convective dredge-up of optically invisible traces of carbon from the deep interior is crucial to account for the observations. Neither the convective dilution/mixing of residual hydrogen nor the accretion of hydrogen or metals can be the dominant drivers of the bifurcation. Finally, we emphasize the importance of improving the equation of state of partially ionized carbon in warm dense helium, a key input for our predictions of the amount of dredged-up carbon.

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S. Blouin, A. Bédard and P. Tremblay
Fri, 5 May 23
57/67

Comments: Under review at MNRAS, submitted on 2023-03-15

Accuracy analysis of the on-board data reduction pipeline for the Polarimetric and Helioseismic Imager on the Solar Orbiter mission [SSA]

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http://arxiv.org/abs/2305.01945


Scientific data reduction on-board deep space missions is a powerful approach to maximise science return, in the absence of wide telemetry bandwidths. The Polarimetric and Helioseismic Imager (PHI) on-board the Solar Orbiter (SO) is the first solar spectropolarimeter that opted for this solution, and provides the scientific community with science-ready data directly from orbit. This is the first instance of full solar spectropolarimetric data reduction on a spacecraft. In this paper, we analyse the accuracy achieved by the on-board data reduction, which is determined by the trade-offs taken to reduce computational demands and to ensure the autonomous operation of the instrument during the data reduction process. We look at the magnitude and nature of errors introduced in the different pipeline steps of the processing. We use an MHD sunspot simulation to isolate the data processing from other sources of inaccuracy. We process the data set with calibration data obtained from SO/PHI in orbit, and compare results calculated on a representative SO/PHI model on ground with a reference implementation of the same pipeline, without the on-board processing trade-offs. Our investigation shows that the accuracy in the Stokes vectors, achieved by the data processing, is at least two orders of magnitude better than what the instrument was designed to achieve. We also found that the errors in the physical parameters are within the accuracy of typical RTE inversions with Milne-Eddington approximation of the atmosphere. This paper demonstrates that the on-board data reduction of the data from SO/PHI does not compromise the accuracy of the processing. This places on-board data processing as a viable alternative for future scientific instruments that would need more telemetry than many missions are able to provide, in particular those in deep space.

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K. Albert, J. Hirzberger, J. Durán, et. al.
Thu, 4 May 23
11/60

Comments: N/A

Observationally guided models for the solar dynamo and the role of the surface field [SSA]

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http://arxiv.org/abs/2305.02253


Theoretical models for the solar dynamo range from simple low-dimensional “toy models” to complex 3D-MHD simulations. Here we mainly discuss appproaches that are motivated and guided by solar (and stellar) observations. We give a brief overview of the evolution of solar dynamo models since 1950s, focussing upon the development of the Babcock-Leighton approach between its introduction in the 1960s and its revival in the 1990s after being long overshadowed by mean-field turbulent dynamo theory. We summarize observations and simple theoretical deliberations that demonstrate the crucial role of the surface fields in the dynamo process and and give quantitative analyses of the generation and loss of toroidal flux in the convection zone as well as of the production of poloidal field resulting from flux emergence at the surface. Furthermore, we discuss possible nonlinearities in the dynamo process suggested by observational results and present models for the long-term variability of solar activity motivated by observations of magnetically active stars and the inherent randomness of the dynamo process.

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R. Cameron and M. Schüssler
Thu, 4 May 23
13/60

Comments: submitted to Space Science Reviews

A hidden population of white dwarfs with atmospheric carbon traces in the Gaia bifurcation [SSA]

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http://arxiv.org/abs/2305.02110


The ESA Gaia space mission has revealed a bifurcation of the white dwarf (WD) sequence on the color magnitude diagram in two branches: A and B. While the A branch consists mostly of WDs with H-rich atmospheres, the B branch is not completely understood. Although invoked to be populated mainly by He-rich WDs, the B branch overlaps a $\sim 0.8M_\odot$ evolutionary track with a pure He envelope, fact that would imply an unexpected peak in the WD mass distribution. In cold He-rich WDs, it is expected that the outer convective zone penetrates into deep C-rich layers, thus leading to a slight C contamination in their surfaces at $\sim 10,000$K. Here we aim at studying the Gaia bifurcation as the natural consequence of C dredge-up by convection in cold He-dominated WDs. Relying on accurate atmosphere models, we provide a new set of evolutionary models for He-rich WDs employing different prescriptions for the C enrichment. On the basis of these models, we made a population synthesis study of the Gaia 100pc WD sample to constrain the models that best fit the bifurcation. Our study shows that He-rich WD models with a slight C contamination below the optical detection limit can accurately reproduce the Gaia bifurcation. We refer to these stars as stealth DQ WDs because they do not exhibit detectable C signatures in their optical spectra, but the presence of C in their atmosphere produces a continuum absorption favouring the emission in bluer wavelengths, thereby creating the B branch of the bifurcation. Also, we show that the mass distribution for He-rich WDs obtained when a stealth C contamination is considered is consistent with the mass distribution for H-rich WDs and with the standard evolutionary channels for their formation. We conclude that stealth DQ WDs can account for the lower branch in the Gaia bifurcation. The C signatures of these stars could be detectable in Ultra-Violet spectra.

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M. Camisassa, S. Torres, M. Hollands, et. al.
Thu, 4 May 23
14/60

Comments: 9 pages, 8 figures, accepted for publication in Astronomy & Astrophysics

Evidence for multiple nucleosynthetic processes from carbon enhanced metal-poor stars in the Carina dwarf spheroidal galaxy [SSA]

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http://arxiv.org/abs/2305.02316


Context: Carbon Enhanced Metal-Poor (CEMP) stars ($\mathrm{[C/Fe]} > 0.7$) are known to exist in large numbers at low metallicity in the Milky Way halo and are important tracers of early Galactic chemical evolution. However, very few such stars have been identified in the classical dwarf spheroidal (dSph) galaxies, and detailed abundances, including neutron-capture element abundances, have only been reported for 12 stars. Aims: We aim to derive detailed abundances of six CEMP stars identified in the Carina dSph and compare the abundances to CEMP stars in other dSph galaxies and the Milky Way halo. This is the largest sample of CEMP stars in a dSph galaxy analysed to date. Methods: 1D LTE elemental abundances are derived via equivalent width and spectral synthesis using high-resolution spectra of the six stars obtained with the MIKE spectrograph at Las Campanas Observatory. Results: Abundances or upper limits are derived for up to 27 elements from C to Os in the six stars. The analysis reveals one of the stars to be a CEMP-no star with very low neutron-capture element abundances. In contrast, the other five stars all show enhancements in neutron-capture elements in addition to their carbon enhancement, classifying them as CEMP-$s$ and -$r/s$ stars. The six stars have similar $\alpha$ and iron-peak element abundances as other stars in Carina, except for the CEMP-no star, which shows enhancement in Na, Mg, and Si. We explore the absolute carbon abundances ($A(\rm C)$) of CEMP stars in dSph galaxies and find similar behaviour as is seen for Milky Way halo CEMP stars, but highlight that CEMP-$r/s$ stars primarily have very high $A(\rm C)$ values. We also compare the neutron-capture element abundances of the CEMP-$r/s$ stars in our sample to recent $i$-process yields, which provide a good match to the derived abundances.

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T. Hansen, J. Simon, T. Li, et. al.
Thu, 4 May 23
15/60

Comments: 14 pages, 5 figures, 9 tables, Accepted for publication in A&A

Self-consistent propagation of flux ropes in realistic coronal simulations [SSA]

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http://arxiv.org/abs/2305.02089


The aim of this paper is to demonstrate the possible use of the new coronal model COCONUT to compute a detailed representation of a numerical CME at 0.1~AU, after its injection at the solar surface and propagation in a realistic solar wind, as derived from observed magnetograms. We present the implementation and propagation of modified Titov-D\’emoulin (TDm) flux ropes in the COCONUT 3D MHD coronal model. The background solar wind is reconstructed in order to model two opposite configurations representing a solar activity maximum and minimum respectively. Both were derived from magnetograms which were obtained by the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamic Observatory (SDO) satellite. We track the propagation of 24 flux ropes, which differ only by their initial magnetic flux. We especially investigate the geometry of the flux rope during the early stages of the propagation as well as the influence of its initial parameters and solar wind configuration on 1D profiles derived at 0.1~AU. At the beginning of the propagation, the shape of the flux ropes varies between simulations during low and high solar activity. We find dynamics that are consistent with the standard CME model, such as the pinching of the legs and the appearance of post-flare loops. Despite the differences in geometry, the synthetic density and magnetic field time profiles at 0.1~AU are very similar in both solar wind configurations. These profiles are similar to those observed further in the heliosphere and suggest the presence of a magnetic ejecta composed of the initially implemented flux rope and a sheath ahead of it. Finally, we uncover relationships between the properties of the magnetic ejecta, such as density or speed and the initial magnetic flux of our flux ropes.

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L. Linan, F. Regnault, B. Perri, et. al.
Thu, 4 May 23
16/60

Comments: 20 pages, 13 figures

Reconnection generated plasma flows in the quasi-separatrix layer in localised solar corona [SSA]

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http://arxiv.org/abs/2305.02277


Multiwavelength observations of the propagating disturbances (PDs), discovered by Atmospheric Imaging Assembly (AIA) onboard Solar Dynamics Observatory (SDO), are analyzed to determine its driving mechanism and physical nature. Two magnetic strands in the localised corona are observed to approach and merge with each other followed by the generation of brightening, which further propagates in a cusp-shaped magnetic channel. Differential emission measure analysis shows an occurrence of heating in this region-of-interest (ROI). We extrapolate potential magnetic field lines at coronal heights from observed Helioseismic and Magnetic Imager (HMI) vector magnetogram via Green’s function method using MPI-AMRVAC. We analyze the field to locate magnetic nulls and quasi-separatrix layers (QSLs) which are preferential locations for magnetic reconnection. Dominant QSLs including a magnetic null are found to exist and match the geometry followed by PDs, therefore, it provides conclusive evidence of magnetic reconnection. In addition, spectroscopic analysis of Interface Region Imaging Spectrograph (IRIS) Si IV 1393.77 {\AA} line profiles show a rise of line-width in the same time range depicting presence of mass motion in the observed cusp-shaped region. PDs are observed to exhibit periodicities of around four minutes. The speeds of PDs measured by Surfing Transform Technique are almost close to each other in four different SDO/AIA bandpasses, i.e., 304, 171, 193 and 131 {\AA} excluding the interpretation of PDs in terms of slow magnetoacoustic waves. We describe comprehensively the observed PDs as quasi-periodic plasma flows generated due to periodic reconnection in vicinity of a coronal magnetic null.

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S. Mondal, A. Srivastava, S. Mishra, et. al.
Thu, 4 May 23
18/60

Comments: 21 Pages; 10 Figures; Accepted for the Publication in The Astrophysical Journal

A deep optical survey of young stars in the Carina Nebula. I. — UBVRI photometric data and fundamental parameters [SSA]

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http://arxiv.org/abs/2305.01887


We present the deep homogeneous $UBVRI$ photometric data of 135,071 stars down to $V\sim23$ mag and I ~ 22 mag toward the Carina Nebula. These stars are cross-matched with those from the previous surveys in the X-ray, near-infrared, and mid-infrared wavelengths as well as the Gaia Early Data Release 3 (EDR3). This master catalog allows us to select reliable members and determine the fundamental parameters distance, size, stellar density of stellar clusters in this star-forming region. We revisit the reddening toward the nebula using the optical and the near-infrared colors of early-type stars. The foreground reddening [E(B-V)_fg] is determined to be 0.35+/-0.02, and it seems to follow the standard reddening law. On the other hand, the total-to-selective extinction ratio of the intracluster medium (R_V,cl) decreases from the central region (Trumpler 14 and 16, R_V,cl ~ 4.5) to the northern region (Trumpler 15, R_V,cl ~ 3.4). It implies that the central region is more dusty than the northern region. We find that the distance modulus of the Carina Nebula to be 11.9+/-0.3 mag (d = 2.4+/-0.35 kpc) using a zero-age main-sequence fitting method, which is in good agreement with that derived from the Gaia EDR3 parallaxes. We also present the catalog of 3,331 pre-main-sequence (PMS) members and 14,974 PMS candidates down to V ~ 22 mag based on spectrophotometric properties of young stars at infrared, optical, and X-ray wavelengths. From the spatial distribution of PMS members and PMS candidates, we confirm that the member selection is very reliable down to faint stars. Our data will have a legacy value for follow-up studies with different scientific purposes.

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H. Hur, B. Lim and M. Chun
Thu, 4 May 23
38/60

Comments: 21 pages, 20 figures, accepted for publication in Journal of the Korean Astronomical Society

Power-2 limb-darkening coefficients for the $uvby$, $UBVRIJHK$, SDSS $ugriz$, Gaia, Kepler, TESS, and CHEOPS photometric systems II. PHOENIX spherically symmetric stellar atmosphere models [SSA]

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http://arxiv.org/abs/2305.01704


Multiple parametric limb-darkening laws have been presented, and there are many available sources of theoretical limb-darkening coefficients (LDCs) calculated using stellar model atmospheres. The power-2 limb-darkening law allows a very good representation of theoretically predicted intensity profiles, but few LDCs are available for this law from spherically symmetric model atmospheres. We therefore present such coefficients in this work. We computed LDCs for the space missions \textit{Gaia}, \textit{Kepler}, TESS, and CHEOPS and for the passbands $uvby$, $UBVRIJHK$, and SDSS $ugriz$, using the \textsc{phoenix-cond} spherical models. We adopted two methods to characterise the truncation point, which sets the limb of the star: the first (M1) uses the point where the derivative d$I(r)$/d$r$ is at its maximum where I(r) is the specific intensity as a function of the normalised radius r corresponding to $\mu_{\rm cri}$, and the second (M2) uses the midpoint between the point $\mu_{\rm cri}$ and the point located at $\mu_{\rm cri-1}$. The LDCs were computed adopting the Levenberg-Marquardt least-squares minimisation method, with a resolution of 900 equally spaced $\mu$ points, and covering 823 model atmospheres for a solar metallicity, effective temperatures of 2300 to 12000\,K, $\log g$ values from 0.0 to 6.0, and microturbulent velocities of 2\,km\,s$^{-1}$. As our previous calculations of LDCs using spherical models included only 100 $\mu$ points, we also updated the calculations for the four-parameter law for the passbands listed above, and compared them with those from the power-2 law. Comparisons between the quality of the fits provided by the power-2 and four-parameter laws show that the latter presents a lower merit function, $\chi^2$, than the former for both cases (M1 and M2). This is important when choosing the best approach for a particular science goal.

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A. Claret and J. Southworth
Thu, 4 May 23
40/60

Comments: N/A

Metallicity and age effects on lithium depletion in solar analogues [SSA]

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http://arxiv.org/abs/2305.01861


The lithium present in the photospheres of solar-type stars is transported to the inner parts by convection, reaching regions even somewhat below the convection zone, by non-standard transport mechanisms. In stars with deeper convective zones, this element can reach regions with temperatures sufficient enough to be destroyed, implying in a lower Li content. More metallic stars show a deepening of their convective zones, so they could deplete more Li in comparison with stars of lower metallicity. In order to verify this effect and its amplitude, we selected stars with ~1 M$_{\odot}$ and metallicities within a factor of two relative to the Sun. We studied a sample of 41 metal-rich and -poor solar analogues, and carried out a joint analysis with a sample of 77 solar twins from our previous work, resulting in a total sample of 118 stars covering the metallicity range -0.3 $\leq$ [Fe/H] $\leq$ +0.3 dex. We employed high-resolution (R = 115 000) and high-signal-to-noise ratio (S/N = 400-1000) HARPS spectra and determined the atmospheric parameters using a line-by-line differential analysis and the Li abundance through spectral synthesis. The ages and masses of the whole sample were improved by refining the isochronal method. We also investigated the impact of planets on Li. We found robust anticorrelations between Li abundance and both metallicity and age, with a significance above 10$\sigma$ in both cases. Our results agree qualitatively with theoretical predictions and are useful to constrain non-standard models of Li depletion, and to better understand transport and mixing mechanisms inside stars.

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G. Martos, J. Meléndez, A. Rathsam, et. al.
Thu, 4 May 23
44/60

Comments: 10 pages, 5 figures, 2 tables

Eclipse observations of V838 Her (Nova Her 1991) during nova eruption [SSA]

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http://arxiv.org/abs/2305.01197


I observed the very fast nova V838 Her (Nova Her 1991, optical peak at 5-5.4 mag) during the fading phase of the nova eruption in 1991. I detected eclipses, for the first time in the world in any nova during eruption, and the epochs of the eclipses were reported to IAU Circular No. 5262. Although these epochs have been referenced in the literature, the light curves of these eclipses remained unpublished. Here, I present these light curves. The phase-averaged light curve around 1991 April 21 (mean V=13.1, 27 d after the optical peak) showed an 0.14 mag primary eclipse and an 0.03 mag secondary eclipse. Combined with the subsequent literature, the eclipses likely appeared after 1991 April 14 (V=12.5). It had been suggested that the accretion disk had already been re-established before this epoch and I found no strong argument against this. The early appearance of the secondary minimum appears to be a phenomenon common to very fast novae and it looks likely to be explained, at least partly, by a strongly heated secondary. This observation reinforces the possible interpretation of the early presence of a transient luminous donor for the fastest nova V1674 Her (Nova Her 2021). As a comparison and my motivation of the observation of V838 Her, I briefly review the early history of V1500 Cyg (Nova Cyg 1975).

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T. Kato
Wed, 3 May 23
1/67

Comments: 10 pages, 3 figures, supplementary data, VSOLJ Variable Star Bulletin No. 115

Structural Analysis of Open Cluster Bochum 2 [SSA]

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http://arxiv.org/abs/2305.01212


We present the results from our deep optical photometric observations of Bochum 2 (Boc2) star cluster obtained using the $1.3$m Devasthal Fast Optical Telescope along with archival photometric data from Pan-STARRS2/2MASS/UKIDSS surveys. We also used high-quality parallax and proper motion data from the $Gaia$ Data Release 3. We found that the Boc2 cluster has a small size ($\sim$1.1 pc) and circular morphology. Using $Gaia$ parallax of member stars and isochrone fitting method, the distance of this cluster is estimated as $3.8\pm0.4$ kpc. We have found that this cluster holds young ($\sim5$ Myr) and massive (O$7-$O$9$) stars as well as an older population of low mass stars. We found that the massive stars have formed in the inner region of the Boc2 cluster in a recent epoch of star formation. We have derived mass function slope ($\Gamma$) in the cluster region as $-2.42\pm0.13$ in the mass range $\sim0.72<$M/M$_{\odot}<2.8$. The tidal radius of the Boc2 cluster ($\sim7-9$) is much more than its observed radius ($\sim1.1$ pc). This suggests that most of the low-mass stars in this cluster are the remains of an older population of stars formed via an earlier epoch of star formation.

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H. Kaur, S. Sharma, A. Durgapal, et. al.
Wed, 3 May 23
7/67

Comments: accepted for publication in Journal of Astrophysics and Astronomy

Analytical and Numerical Analysis of Circumbinary Disk Dynamics – I: Coplanar Systems [SSA]

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http://arxiv.org/abs/2305.01533


We present an analytical and numerical study of a system composed of a stellar binary pair and a massless, locally isothermal viscous accretion disk that is coplanar to the binary orbital plane. Analytically, we study the effect of the binary’s gravitational potential over short timescales through the study of stability for epicyclic orbits, and over long timescales by revisiting the concept of resonant torques. Numerically, we perform two-dimensional Newtonian numerical simulations of the disk-binary system over a range of binary mass ratios. We find that the results of our simulations are consistent with previous numerical studies. We additionally show, by comparison of the analytical and numerical results, that the circumbinary gap is maintained on the orbital timescale through the driving of epicyclic instabilities, and does not depend on resonant torquing, contrary to standard lore. While our results are applicable to any disk-binary system, we highlight the importance of this result in the search for electromagnetic and gravitational-wave signatures from supermassive black-hole binaries.

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S. Mahesh, S. McWilliams and M. Pirog
Wed, 3 May 23
15/67

Comments: N/A

Hale cycle in solar hemispheric radio flux and sunspots: Evidence for a northward shifted relic field [SSA]

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http://arxiv.org/abs/2305.01030


Solar and heliospheric parameters can depict notable differences between the northern and southern hemisphere. Although hemispheric asymmetries of some heliospheric parameters vary systematically with Hale cycle, this is not common for solar parameters. Also, no physical mechanism exists which can explain systematic hemispheric asymmetries. We use a novel method of high heliolatitudes to increase the fraction of one hemisphere in solar 10.7cm radio fluxes and sunspot numbers. We calculate sets of hemispheric high-latitude radio fluxes and sunspot numbers with increasing heliographic latitude during the last 75 years. We also normalise these fluxes by yearly means in order to study their continuous variation. We find that cycle maximum radio fluxes and sunspot numbers in each odd cycle (19, 21, 23) are larger at northern high latitudes, while in all even cycles (18, 20, 22 24) they are larger at southern latitudes. This alternation indicates a new form of Hale cycle variation in solar activity. Hemispheric differences at cycle maxima are 15% for radio flux and 23% for sunspot numbers. The difference is largest during cycle 19 and smallest in cycle 24. Continuous fluxes depict a Hale cycle in both hemispheres, with an opposite phase and amplitude of 5% in north and 4% in south. Hemispheric Hale cycle can be explained if there is a northward directed relic magnetic field, which is shifted northward. In odd cycles, the northern hemisphere is enhanced more than the southern hemisphere and, in even cycles, the northern hemisphere is reduced more than the southern hemisphere. The decrease of asymmetry during the 7 cycles can be explained if the relic shift oscillates at the 210-year Suess/deVries period. Gleissberg cycle consists of one off-equator excursion of the relic. Relic field in the Sun also offers a possibility for century-scale forecasting of solar activity.

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K. Mursula
Wed, 3 May 23
21/67

Comments: Accepted to be published in Astronomy and Astrophysics

Massive pre-main-sequence stars in M17: $1^{\rm st}$ and $2^{\rm nd}$ overtone CO bandhead emission and the thermal infrared [SSA]

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http://arxiv.org/abs/2305.01436


Recently much progress has been made in probing the embedded stages of massive star formation, pointing to formation scenarios akin to a scaled up version of low-mass star formation. However, the latest stages of massive star formation have rarely been observed. Using 1st and 2nd overtone CO bandhead emission and near- to mid-infrared photometry we aim to characterize the remnant formation disks around 5 unique pre-main-sequence (PMS) stars with masses $6-12~\rm M_{\odot}$, that have constrained stellar parameters thanks to their detectable photospheres. We seek to understand this emission and the disks it originates from in the context of the evolutionary stage of the studied sources. We use an analytic LTE disk model to fit the CO bandhead and the dust emission, found to originate in different disk regions. For the first time we modeled the 2nd overtone emission. Furthermore, we fit continuum normalized bandheads and show the importance of this in constraining the emission region. We also include $^{13}\rm CO$ in our models as an additional probe of the young nature of the studied objects. We find that the CO emission originates in a narrow region close to the star (<1 AU) and under very similar disk conditions (temperatures and densities) for the different objects. This is consistent with previous modeling of this emission in a diverse range of young stellar objects. We discuss these results in the context of the positions of these PMS stars in the Hertzsprung-Russel diagram and the CO emission’s association with early age and high accretion rates in (massive) young stellar objects. We conclude that, considering their mass range and for the fact that their photospheres are detected, the M17 PMS stars are observed in a relatively early formation stage. They are therefore excellent candidates for longer wavelength studies to further constrain the end stages of massive star formation.

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J. Poorta, M. Ramírez-Tannus, A. Koter, et. al.
Wed, 3 May 23
33/67

Comments: 21 pages, 12 figures

Effects of the centrifugal force on stellar dynamo simulations [SSA]

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http://arxiv.org/abs/2305.01312


The centrifugal force is often omitted in simulations of stellar convection. This force might be important in rapidly rotating stars such as solar analogues due to its $\Omega^2$ scaling, where $\Omega$ is the rotation rate of the star. We study the effects of the centrifugal force in a set of 21 semi-global stellar dynamo simulations with varying rotation rates. Among these, we include three control runs aimed at distinguishing the effects of the centrifugal force from the nonlinear evolution of the solutions. We solve the 3D MHD equations with the Pencil Code in a solar-like convective zone in a spherical wedge setup with a $2\pi$ azimuthal extent. We decompose the magnetic field in spherical harmonics and study the migration of azimuthal dynamo waves (ADWs), energy of different large-scale magnetic modes, and differential rotation. In the regime with the lowest rotation rates, $\Omega = 5-10\Omega_\odot$, where $\Omega_\odot$ is the rotation rate of the Sun, we see no marked changes in neither the differential rotation nor the magnetic field properties. For intermediate rotation with $\Omega = 20-25\Omega_\odot$ we identify an increase of the differential rotation as a function of centrifugal force. The axisymmetric magnetic energy tends to decrease with centrifugal force while the non-axisymmetric one increases. The ADWs are also affected, especially the propagation direction. In the most rapidly rotating set with $\Omega=30\Omega_\odot$, these changes are more pronounced and in one case the propagation direction of the ADW changes from prograde to retrograde. Control runs suggest that the results are a consequence of the centrifugal force and not due to the details of the initial conditions or the history of the run. We find that the differential rotation and properties of the ADWs change as a function of the centrifugal force only when rotation is rapid enough.

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F. Navarrete, P. Käpylä, D. Schleicher, et. al.
Wed, 3 May 23
48/67

Comments: 8 pages, 7 figures, submitted to A&A

Theoretical tidal evolution constants for stellar models from the pre-main sequence to the white dwarf stage Apsidal motion constants, moment of inertia, and gravitational potential energy [SSA]

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http://arxiv.org/abs/2305.01627


One of the most reliable means of studying the stellar interior is through the apsidal motion in double line eclipsing binary systems since these systems present errors in masses, radii, and effective temperatures of only a few per cent. On the other hand, the theoretical values of the apsidal motion to be compared with the observed values depend on the stellar masses of the components and more strongly on their radii (fifth power).The main objective of this work is to make available grids of evolutionary stellar models that, in addition to the traditional parameters (e.g. age, mass, log g, T${\rm eff}$), also contain the necessary parameters for the theoretical study of apsidal motion and tidal evolution. This information is useful for the study of the apsidal motion in eclipsing binaries and their tidal evolution, and can also be used for the same purpose in exoplanetary systems. All models were computed using the MESA package. We consider core overshooting for models with masses $\ge$ 1.2 M$\odot$. For the amount of core overshooting we adopted a recent relationship for mass $\times$ core overshooting. We adopted for the mixing-length parameter $\alpha_{\rm MLT}$ the value 1.84 (the solar-calibrated value). Mass loss was taken into account in two evolutionary phases. The models were followed from the pre-main sequence phase to the white dwarf (WD) stage.The evolutionary models containing age,luminosity, log g, and Teff, as well as the first three harmonics of the internal stellar structure (k$_2$, k$_3$, and k$_4$), the radius of gyration $\beta$ y, and the dimensionless variable $\alpha$, related to gravitational potential energy, are presented in 69 tables covering three chemical compositions: [Fe/H] = -0.50, 0.00, and 0.50. Additional models with different input physics are available.

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A. Claret
Wed, 3 May 23
51/67

Comments: N/A

Direct assessment of SDO/HMI helioseismology of active regions on the Sun's far side using SO/PHI magnetograms [SSA]

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http://arxiv.org/abs/2305.01594


Earth-side observations of solar p modes can be used to image and monitor magnetic activity on the Sun’s far side. Here we use magnetograms of the far side obtained by the Polarimetric and Helioseismic Imager (PHI) onboard Solar Orbiter (SO) to directly assess — for the first time — the validity of far-side helioseismic holography. We wish to co-locate the positions of active regions in helioseismic images and magnetograms, and to calibrate the helioseismic measurements in terms of magnetic field strength. We identify three magnetograms on 18 November 2020, 3 October 2021, and 3 February 2022 displaying a total of six active regions on the far side. The first two dates are from SO’s cruise phase, the third from the beginning of the nominal operation phase. We compute contemporaneous seismic phase maps for these three dates using helioseismic holography applied to time series of Dopplergrams from the Helioseismic and Magnetic Imager (HMI) on the Solar Dynamics Observatory (SDO). Among the six active regions seen in SO/PHI magnetograms, five active regions are identified on the seismic maps at almost the same positions as on the magnetograms. One region is too weak to be detected above the seismic noise. To calibrate the seismic maps, we fit a linear relationship between the seismic phase shifts and the unsigned line-of-sight magnetic field averaged over the active region areas extracted from the SO/PHI magnetograms. SO/PHI provides the strongest evidence so far that helioseismic imaging provides reliable information about active regions on the far side, including their positions, areas, and mean unsigned magnetic field.

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D. Yang, L. Gizon, H. Barucq, et. al.
Wed, 3 May 23
67/67

Comments: 10 pages, 9 figures

An Eclipsing Binary Comprising Two Active Red Stragglers of Identical Mass and Synchronized Rotation: A Post-Mass-Transfer System or Just Born That Way? [SSA]

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http://arxiv.org/abs/2305.00134


We report the discovery of 2M0056-08 as an equal-mass eclipsing binary (EB), comprising two red straggler stars (RSSs) with an orbital period of 33.9 d. Both stars have masses of 1.419 Msun, identical to within 0.2%. Both stars appear to be in the early red-giant phase of evolution; however, they are far displaced to cooler temperatures and lower luminosities compared to standard stellar models. The broadband spectral energy distribution shows NUV excess and X-ray emission, consistent with chromospheric and coronal emission from magnetically active stars; indeed, the stars rotate more rapidly than typical red giants and they evince light curve modulations due to spots. These modulations also reveal the stars to be rotating synchronously with one another. There is evidence for excess FUV emission and long-term modulations in radial-velocities; it is not clear whether these are also attributable to magnetic activity or if they reveal a tertiary companion. Stellar evolution models modified to account for the effects of spots can reproduce the observed radii and temperatures of the RSSs. If the system possesses a white dwarf tertiary, then mass-transfer scenarios could explain the manner by which the stars came to possess such remarkably identical masses and by which they came to be sychronized. However, if the stars are presumed to have been formed as identical twins, and they managed to become tidally synchronized as they evolved toward the red giant branch, then all of the features of the system can be explained via activity effects, without requiring a complex dynamical history.

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K. Stassun, G. Torres, M. Kounkel, et. al.
Tue, 2 May 23
5/57

Comments: 23 pages, 15 figures, accepted for publication in ApJ

M giants with IGRINS I. Stellar parameters and $α$-abundance trends of the solar neighborhood population [SSA]

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http://arxiv.org/abs/2305.00486


Cool stars, such as M giants, can only be analysed in the near-infrared (NIR) regime due to the ubiquitous TiO features in optical spectra of stars with Teff < 4000 K. In dust obscured regions, like the inner bulge and Galactic Center, the intrinsically bright M giants observed in the NIR is an optimal option to determine their stellar abundances. Due to uncertainties in photometric methods, a method to determine the stellar parameters for M giants from the NIR spectra themselves is needed.
We have carried out new observations of 44 M giant stars (also in APOGEE DR17) with IGRINS (R=45,000) mounted on the Gemini South telescope. We also obtained HK band IGRINS spectra of six nearby well-studied M giants from the IGRINS spectral library. Using this sample, we have developed a method to determine the stellar parameters for M giants from the NIR spectra by spectral synthesis using SME. The method is validated using the six nearby well-studied M-giants. We demonstrate the accuracy and precision by determining stellar parameters and $\alpha$-element trends versus metallicity for solar neighbourhood M giants.
The effective temperatures that we derive (tested for 3400$\lesssim$ Teff $\lesssim$4000\,K) agree excellently with the six nearby M giants which indicates that the accuracy is indeed high. For the 43 solar neighborhood M giants, our Teff, logg, [Fe/H], $\xi_\mathrm{micro}$, [C/Fe], [N/Fe], and [O/Fe] are in unison with APOGEE with mean differences and scatter (our method – APOGEE) of -67$\pm$33 K, -0.31$\pm$0.15 dex, 0.02$\pm$0.05 dex, 0.22$\pm$0.13 km/s, -0.05$\pm$0.06 dex, 0.06$\pm$0.06 dex, and 0.02$\pm$0.09 dex, respectively. The $\alpha$-element trends versus metallicity for Mg, Si, Ca and Ti are consistent with both APOGEE DR17 trends for the same stars as well as with the GILD optical trends. We also find clear enhancement in abundances for thick disc stars.

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G. Nandakumar, N. Ryde, L. Casagrande, et. al.
Tue, 2 May 23
6/57

Comments: 27 Pages including appendix of 10 pages, 15 figures, Accepted for publication in A&A

Ensemble Learning for CME Arrival Time Prediction [SSA]

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http://arxiv.org/abs/2305.00258


The Sun constantly releases radiation and plasma into the heliosphere. Sporadically, the Sun launches solar eruptions such as flares and coronal mass ejections (CMEs). CMEs carry away a huge amount of mass and magnetic flux with them. An Earth-directed CME can cause serious consequences to the human system. It can destroy power grids/pipelines, satellites, and communications. Therefore, accurately monitoring and predicting CMEs is important to minimize damages to the human system. In this study we propose an ensemble learning approach, named CMETNet, for predicting the arrival time of CMEs from the Sun to the Earth. We collect and integrate eruptive events from two solar cycles, #23 and #24, from 1996 to 2021 with a total of 363 geoeffective CMEs. The data used for making predictions include CME features, solar wind parameters and CME images obtained from the SOHO/LASCO C2 coronagraph. Our ensemble learning framework comprises regression algorithms for numerical data analysis and a convolutional neural network for image processing. Experimental results show that CMETNet performs better than existing machine learning methods reported in the literature, with a Pearson product-moment correlation coefficient of 0.83 and a mean absolute error of 9.75 hours.

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K. Alobaid and J. Wang
Tue, 2 May 23
8/57

Comments: 13 pages, 8 figures

The Effelsberg survey of FU~Orionis and EX~Lupi objects II. — H$_2$O maser observations [SSA]

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http://arxiv.org/abs/2305.00736


FU Orionis (FUor) and EX Lupi (EXor) type objects are two groups of peculiar and rare pre-main sequence low-mass stars that are undergoing powerful accretion outbursts during their early stellar evolution. Water masers are widespread in star forming regions and are powerful probes of mass accretion and ejection, but little is known about the prevalence of them toward FUors/EXors. We perform the first systematic search for the 22.2 GHz water maser line in FUors/EXors to determine its overall incidence to perform follow-up high angular resolution observations. We used the Effelsberg 100-m radio telescope to observe the 22.2 GHz H2O maser toward a sample of 51 objects. We detect 5 water masers; 3 are associated with eruptive stars, resulting in a 6% detection rate for eruptive sources. These detections include one EXor, V512 Per (also known as SVS 13 or SVS 13A), and two FUors, Z CMa and HH 354 IRS. This is the first reported detection of water maser emission towards HH 354 IRS. We detect water maser emission in our pointing towards the FUor binary RNO 1B/1C, which most likely originates from the nearby deeply embedded source IRAS 00338+6312 (~4”, from RNO 1B/1C). Emission was also detected from H$_2$O(B) (also known as SVS 13C), a Class 0 source ~30”, from the EXor V512 Per. The peak flux density of H$_2$O(B) in our observations, 498.7 Jy, is the highest observed to date. In addition to the two non-eruptive Class 0 sources (IRAS 00338+6312 and H$_2$O(B) /SVS 13C), we detect maser emission towards one Class 0/I (HH 354 IRS) and two Class I (V512 Per and Z CMa) eruptive stars. We demonstrate the presence of 22.2 GHz water maser emission in FUor/EXor systems, opening the way to radio interferometric observations to study these eruptive stars on small scales. Comparing our data with historical observations suggest that multiple water maser flares have occurred in both V512 Per and H$_2$O(B).

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Z. Szabó, Y. Gong, W. Yang, et. al.
Tue, 2 May 23
15/57

Comments: 12 pages, 8 figures, accepted for publication in Astronomy & Astrophysics

Limitations and biases in the retrieval of the polar magnetic field I: the role of the magnetic filling factor in Milne-Eddington inversions of simulated Hinode/SP data [SSA]

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http://arxiv.org/abs/2305.00924


We study the extent to which Milne-Eddington inversions are able to retrieve and characterize the magnetic landscape of the solar poles from observations by the spectropolarimeter onboard Hinode. In particular, we evaluate whether a variable magnetic filling factor is an adequate modeling technique for retrieving the intrinsic magnetic properties from every pixel in the polar field of view. We first generate synthetic spectra emerging from a numerical simulation of a “plage” region at an inclined line of sight of 65$^{\circ}$, and degrade the data to emulate real observations. Then, we invert the synthetic spectra with two Milne-Eddington inversion codes that feature different treatments of the magnetic filling factor, and relate the retrieved magnetic quantities back to their original values in the simulation cube. We find that while the apparent retrieved magnetic properties map well the spatially-degraded simulation, the intrinsic magnetic quantities bear little relation to the magnetic field at the native resolution of the simulation. We discuss the systematic biases caused by line-of-sight foreshortening, spatial degradation, photon noise and modeling assumptions embedded in the inversion algorithm.

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R. Centeno, I. Milić, M. Rempel, et. al.
Tue, 2 May 23
20/57

Comments: Accepted for publication in ApJ

The IACOB project IX. Building a modern empirical database of Galactic O9-B9 supergiants: sample selection, description, and completeness [SSA]

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http://arxiv.org/abs/2305.00305


Blue supergiants (BSGs) are important objects to study the intermediate phases of massive star evolution, helping to constrain evolutionary models. However, the lack of a holistic study of a statistically significant and unbiased sample of these objects makes several long-standing questions about their nature to remain unsolved. The present and other upcoming papers of the IACOB series are focused in studying – from a pure empirical point of view – a sample of 500 Galactic O9 – B9 stars with luminosity classes I and II (plus 250 late O- and early B-type stars with luminosity classes III, IV and V) and covering distances up to 4 kpc from the Sun. We compile an initial set of 11000 high-resolution spectra of 1600 Galactic late O- and B-type stars. We use a new novel spectroscopic strategy based on a simple fitting of the Hbeta line to select stars in a specific region of the spectroscopic HR diagram. We evaluate the completeness of our sample using the Alma Luminous Star catalog (ALS III) and Gaia-DR3 data. We show the benefits of the proposed strategy for identifying BSGs descending from stellar objects born as O-type stars, in the context of single star evolution. The resulting sample reaches a high level of completeness with respect to the ALS III catalog, gathering the 80% for all-sky targets brighter than Bmag < 9 located within 2 kpc. However, we identify the need for new observations in specific regions of the Southern hemisphere. In conclusion, we have explored a very fast and robust method to select BSGs, providing a valuable tool for large spectroscopic surveys like WEAVE-SCIP or 4MIDABLE-LR, and highlighting the risk of using spectral classifications from the literature. Upcoming works will make use of this large and homogeneous spectroscopic sample to study specific properties of these stars in detail. We initially provide first results about their rotational properties.

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A. Burgos, S. Simón-Díaz, M. Urbaneja, et. al.
Tue, 2 May 23
21/57

Comments: Almost accepted for publication in Astronomy and Astrophysics. 59 pages, 20 figures

Global energetics of solar powerful events on 6 September 2017 [SSA]

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http://arxiv.org/abs/2305.00381


Solar flares and coronal mass ejections (CMEs) are thought to be the most powerful events on the Sun. They can release energy as high as 10^32 erg in tens of minutes,and could produce solar energetic particles (SEPs) in the interplanetary space. We explore global energy budgets of solar major eruptions on 6 September 2017, including the energy partition of a powerful solar flare, the energy budget of the accompanied CME and SEPs. In the wavelength range shortward of 222 nm, a major contribution of the flare radiated energy is in the soft X-ray (SXR) 0.1-7 nm domain. The flare energy radiated at wavelengths of Ly-alpha and middle ultraviolet is larger than that radiated in the extreme ultraviolet wavelength, but it is much less than that radiated in the SXR waveband. The total flare radiated energy could be comparable to the thermal and nonthermal energies. The energies carried by the major flare and its accompanied CME are roughly equal, and they are both powered by the magnetic free energy in the AR NOAA 12673. Moreover, the CME is efficient in accelerating SEPs, and that the prompt component (whether it comes from the solar flare or the CME) contributes only a negligible fraction.

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D. Li, A. Warmuth, J. Wang, et. al.
Tue, 2 May 23
56/57

Comments: accepted for publication in Research in Astronomy and Astrophysics

The "canonical" White Dwarf Cooling Sequence of M5 [SSA]

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http://arxiv.org/abs/2304.14847


Recently, a new class of white dwarfs (dubbed “slowly cooling WDs”) has been identified in two globular clusters (namely M13 and NGC 6752) showing a horizontal branch (HB) morphology with an extended blue tail. The cooling rate of these WDs is reduced by stable thermonuclear hydrogen burning in their residual envelope, and they are thought to be originated by stars that populate the blue tail of the HB and then skip the asymptotic giant branch phase. Consistently, no evidence of such kind of WDs has been found in M3, a similar cluster with no blue extension of the HB. To further explore this phenomenon, we took advantage of deep photometric data acquired with the Hubble Space Telescope in the near-ultraviolet and investigate the bright portion of the WD cooling sequence in M5, another Galactic globular cluster with HB morphology similar to M3. The normalized WD luminosity function derived in M5 turns out to be impressively similar to that observed in M3, in agreement with the fact that the stellar mass distribution along the HB of these two systems is almost identical. The comparison with theoretical predictions is consistent with the fact that the cooling sequence in this cluster is populated by canonical (fast cooling) WDs. Thus, the results presented in this paper provide further support to the scenario proposing a direct causal connection between the slow cooling WD phenomenon and the horizontal branch morphology of the host stellar cluster.

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J. Chen, F. Ferraro, M. Salaris, et. al.
Mon, 1 May 23
8/51

Comments: 12 pages, 8 figures, accepted in the ApJ

A heat-wave of accretion energy traced by masers in the G358-MM1 high-mass protostar [SSA]

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http://arxiv.org/abs/2304.14739


High-mass stars are thought to accumulate much of their mass via short, infrequent bursts of disk-aided accretion. Such accretion events are rare and difficult to observe directly but are known to drive enhanced maser emission. In this Letter we report high-resolution, multi-epoch methanol maser observations toward G358.93-0.03 which reveal an interesting phenomenon; the sub-luminal propagation of a thermal radiation “heat-wave” emanating from an accreting high-mass proto-star. The extreme transformation of the maser emission implies a sudden intensification of thermal infrared radiation from within the inner (40 mas, 270 au) region. Subsequently, methanol masers trace the radial passage of thermal radiation through the environment at $\geq$ 4-8\% the speed of light. Such a high translocation rate contrasts with the $\leq$ 10 km s$^{-1}$ physical gas motions of methanol masers typically observed using very long baseline interferometry (VLBI). The observed scenario can readily be attributed to an accretion event in the high-mass proto-star G358.93-0.03-MM1. While being the third case in its class, G358.93-0.03-MM1 exhibits unique attributes hinting at a possible `zoo’ of accretion burst types. These results promote the advantages of maser observations in understanding high-mass star formation, both through single-dish maser monitoring campaigns and via their international cooperation as VLBI arrays.

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R. Burns, K. Sugiyama, T. Hirota, et. al.
Mon, 1 May 23
9/51

Comments: Published in Nature Astronomy in 2020

An extreme ultraviolet wave associated with the possible expansion of sheared arcades [SSA]

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http://arxiv.org/abs/2304.14862


Context. Solar extreme ultraviolet (EUV) waves are propagating disturbances in the corona, and they usually accompany with various solar eruptions, from large-scale coronal mass ejections to small-scale coronal jets. Aims. Generally, it is believed that EUV waves are driven by the rapid expansion of coronal loops overlying the erupting cores. In this Letter, we present an exception of EUV wave that was not triggered by the expansion of coronal loops overlying the erupting core. Methods. Combining the multiwavelength observations from multiple instruments, we studied the event in detail. Results. The eruption was restricted in the active region (AR) and disturbed the nearby sheared arcades (SAs) connecting the source AR to a remote AR. Interestingly, following the disturbance, an EUV wave formed close to the SAs, but far away from the eruption source. Conclusions. All the results showed that the EUV wave had a closer temporal and spatial relationship with the disappearing part of SAs than the confined eruption. Hence, we suggest that the EUV wave was likely triggered by the expansion of some strands of SAs, rather than the expansion of erupting loops. It can be a possible complement for the driving mechanisms of EUV waves.

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Y. Liu, R. Zheng, L. Zhang, et. al.
Mon, 1 May 23
10/51

Comments: 9 pages, 6 figures

Why "solar tsunamis" rarely leave their imprints in the chromosphere [SSA]

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http://arxiv.org/abs/2304.14859


Solar coronal waves frequently appear as bright disturbances that propagate globally from the eruption center in the solar atmosphere, just like the tsunamis in the ocean on Earth. Theoretically, coronal waves can sweep over the underlying chromosphere and leave an imprint in the form of Moreton wave, due to the enhanced pressure beneath their coronal wavefront. Despite the frequent observations of coronal waves, their counterparts in the chromosphere are rarely detected. Why the chromosphere rarely bears the imprints of solar tsunamis remained a mystery since their discovery three decades ago. To resolve this question, all coronal waves and associated Moreton waves in the last decade have been initially surveyed, though the detection of Moreton waves could be hampered by utilising the low-quality H$\alpha$ data from Global Oscillations Network Group. Here, we present 8 cases (including 5 in Appendix) of the coexistence of coronal and Moreton waves in inclined eruptions where it is argued that the extreme inclination is key to providing an answer to address the question. For all these events, the lowest part of the coronal wavefront near the solar surface appears very bright, and the simultaneous disturbances in the solar transition region and the chromosphere predominantly occur beneath the bright segment. Therefore, evidenced by observations, we propose a scenario for the excitation mechanism of the coronal-Moreton waves in highly inclined eruptions, in which the lowest part of a coronal wave can effectively disturb the chromosphere even for a weak (e.g., B-class) solar flare.

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R. Zheng, Y. Liu, W. Liu, et. al.
Mon, 1 May 23
14/51

Comments: 24 pages, 14 figures

Cyclic Variability in Brightness of the Young Solar Analog BE Ceti [SSA]

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http://arxiv.org/abs/2304.14794


BE Cet is a young solar analog with an age of 0.6 Gyr and a rotation period of 7.655 days. According to chromospheric and photospheric indices, its activity is higher than the solar one. An analysis of photometric data on the time interval between 1977 and 2019 shows the presence of only 6.76 yr cyclic variations in the mean brightness with an amplitude of 0.02 mag. The obtained cycle is 1-2 yr shorter in comparison with the chromospheric cycle determined earlier, whose length was estimated to be 9 or 7.6 yr. Parameters of the cycle, its amplitude and duration change slightly in different epochs. The short-term light variations due to rotational modulation occur with an increase in amplitude up to 0.05 mag near the activity cycle minimum and a decrease in its maximum. Some events of a rapid increase in brightness of 0.2-0.6 mag may be considered as flares.

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N. Bondar’ and M. Katsova
Mon, 1 May 23
20/51

Comments: 6 pages, 3 figures, 1 table

Revealing the Binarity of HD 36030 — One of the Hottest Flare Stars [SSA]

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http://arxiv.org/abs/2304.14627


The Kepler and TESS space missions significantly expanded our knowledge of what types of stars display flaring activity by recording a vast amount of super-flares from solar-like stars, as well as detecting flares from hotter stars of A-F spectral types. Currently, we know that flaring occurs in the stars as hot as B-type ones. However, the structures of atmospheres of hot B-A stars crucially differ from the ones of late types, and thus the occurrence of flaring in B-A type stars requires some extension of our theoretical views of flare formation and therefore a detailed study of individual objects. Here we present the results of our spectral and photometric study of HD 36030, which is a B9 V star with flares detected by the TESS satellite. The spectra we acquired suggest that the star is in a binary system with a low-mass secondary component, but the light curve lacks any signs of periodic variability related to orbital motion or surface magnetic fields. Because of that, we argue that the flares originate due to magnetic interaction between the components of the system.

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O. Maryeva, P. Németh and S. Karpov
Mon, 1 May 23
24/51

Comments: 16 pages, 10 figures, 3 tables

A dynamical model for IRAS 00500+6713: the remnant of a type Iax supernova SN 1181 hosting a double degenerate merger product WD J005311 [SSA]

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http://arxiv.org/abs/2304.14669


IRAS 00500+6713 is a hypothesized remnant of a type Iax supernova SN 1181. Multi-wavelength observations have revealed its complicated morphology; a dusty infrared ring is sandwiched by the inner and outer X-ray nebulae. We analyze the archival X-ray data taken by XMM-Newton and Chandra to constrain the angular size, mass, and metal abundance of the X-ray nebulae, and construct a theoretical model describing the dynamical evolution of IRAS 00500+6713, including the effects of the interaction between the SN ejecta and the intense wind enriched with carbon burning ashes from the central white dwarf (WD) J005311. We show that the inner X-ray nebula corresponds to the wind termination shock while the outer X-ray nebula to the shocked interface between the SN ejecta and the interstellar matter. The observed X-ray properties can be explained by our model with an SN explosion energy of $E_\mathrm{ej} = (0.77 \mbox{–} 1.1)\times 10^{48}$~erg, an SN ejecta mass of $M_\mathrm{ej} = 0.18\mbox{–}0.53~M_\odot$, if the currently observed wind from WD J005311 started to blow $t_\mathrm{w} \gtrsim 810$ yr after the explosion, i.e., approximately after A.D. 1990. The inferred SN properties are compatible with those of Type Iax SNe and the timing of the wind launch may correspond to the Kelvin-Helmholtz contraction of the oxygen-neon core of WD J005311 that triggered a surface carbon burning. Our analysis supports that IRAS 00500+6713 is the remnant of SN Iax 1181 produced by a double degenerate merger of oxygen-neon and carbon-oxygen WDs, and WD J005311 is the surviving merger product.

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T. Ko, H. Suzuki, K. Kashiyama, et. al.
Mon, 1 May 23
27/51

Comments: 21 pages, 12 figures, 4 tables

Solar wind parameters in rising phase of solar cycle 25 [SSA]

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http://arxiv.org/abs/2304.14707


Solar activity and solar wind parameters decreased significantly in solar cycles (SCs) 23-24. In this paper, we analyze solar wind measurements at the rising phase of SC 25 and compare them with similar data from the previous cycles. For this purpose, we simultaneously selected the OMNI database data for 1976-2022, both by phases of the 11-year solar cycle and by large-scale solar wind types (in accordance with IKI’s catalog, see this http URL ), and calculated the mean values of the parameters for the selected datasets. The obtained results testify in favor of the hypothesis that the continuation of this cycle will be similar to the previous cycle 24, i.e. SC 25 will be weaker than SCs 21 and 22.

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Y. Yermolaev, I. Lodkina, A. Khokhlachev, et. al.
Mon, 1 May 23
28/51

Comments: 11 pages, 7 figures

Rotation and activity in late-type members of the young cluster ASCC 123 [SSA]

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http://arxiv.org/abs/2304.14743


ASCC 123 is a little-studied young and dispersed open cluster. Recently, we conducted the first research devoted to it. In this paper, we complement our previous work with TESS photometry for the 55 likely members of the cluster. We pay special attention to seven of these high-probability members, all with FGK spectral types, for which we have high-resolution spectra from our preceding work. By studying the TESS light curves of the cluster members we determine the rotational period and the amplitude of the rotational modulation for 29 objects. The analysis of the distribution of the periods allows us to estimate a gyrochronogical age for ASCC 123 similar to that of the Pleiades, confirming the value obtained in our previous investigation. A young cluster age is also suggested by the distribution of variation amplitudes. In addition, for those stars with spectroscopic data we calculate the inclination of their rotation axis. These values appear to follow a random distribution, as already observed in young clusters, with no indication of spin alignment. However, our sample is too small to confirm this on more solid statistical grounds. Finally, for these seven stars we study the level of magnetic activity from the H$\alpha$ and CaII H&K lines. Despite the small number of data points, we find a correlation of the H$\alpha$ and CaII flux with Rossby number. The position of these stars in flux–flux diagrams follows the general trends observed in other active late-type stars.

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A. Frasca, J. Alonso-Santiago, G. Catanzaro, et. al.
Mon, 1 May 23
31/51

Comments: Accepted for publication in Monthly Notices of the Royal Astronomical Society. 14 pages, 17 figures

How negative feedback and the ambient environment limit the influence of recombination in common envelope evolution [SSA]

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http://arxiv.org/abs/2304.14840


We perform 3D hydrodynamical simulations to study recombination and ionization during the common envelope (CE) phase of binary evolution, and develop techniques to track the ionic transitions in time and space. We simulate the interaction of a $2\,M_\odot$ red giant branch primary and a $1\,M_\odot$ companion modeled as a particle. We compare a run employing a tabulated equation of state (EOS) that accounts for ionization and recombination, with a run employing an ideal gas EOS. During the first half of the simulations, $\sim15$ per cent more mass is unbound in the tabulated EOS run due to the release of recombination energy, but by simulation end the difference has become negligible. We explain this as being a consequence of (i) the tabulated EOS run experiences a shallower inspiral and hence smaller orbital energy release at late times because recombination energy release expands the envelope and reduces drag, and (ii) collision and mixing between expanding envelope gas, ejecta and circumstellar ambient gas assists in unbinding the envelope, but does so less efficiently in the tabulated EOS run where some of the energy transferred to bound envelope gas is used for ionization. The rate of mass unbinding is approximately constant in the last half of the simulations and the orbital separation steadily decreases at late times. A simple linear extrapolation predicts a CE phase duration of $\sim2\,\mathrm{yr}$, after which the envelope would be unbound.

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L. Chamandy, J. Carroll-Nellenback, E. Blackman, et. al.
Mon, 1 May 23
32/51

Comments: Submitted to MNRAS

Observations of planet forming disks in multiple stellar systems [SSA]

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http://arxiv.org/abs/2304.14450


The demographic of circumstellar disks, the birthplaces of planets, is diverse and rich in disks featuring rings, gaps, spirals, filaments, and arcs. Many studies revealing these disk structures have focused on objects around single stars and disks in isolation. The scenario is more complex if binarity or multiplicity is involved; most stars are part of multiple systems in crowded star-forming regions. How does the presence of one or more stellar companions affect the shape and size of the circumstellar disks? Here we review the landscape of results from optical, infrared, and (sub-) millimeter observations of the effects of multiplicity on protoplanetary disks, emphasizing the demographic studies of nearby molecular clouds and the high-resolution studies of multiple disk systems.

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A. Zurlo, R. Gratton, S. Pérez, et. al.
Mon, 1 May 23
39/51

Comments: Invited review accepted in EPJ+

A runaway T-Tauri star leaving an extended trail [SSA]

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http://arxiv.org/abs/2304.14759


Aims. We address the problem of young stellar objects that are found too far away from possible star formation sites. Different mechanisms have been proposed before to explain this unexpected circumstance. The idea of high-velocity protostars is one of these mechanisms, although observational support is not always easy to obtain. We aim to shed light on this issue after the serendipitous discovery of a related stellar system. Methods. Following the inspection of archival infrared data, a peculiar anonymous star was found that apparently heads a long tail that resembles a wake-like feature. We conducted a multiwavelength analysis including photometry, astrometry, and spectroscopy. Together with theoretical physical considerations, this approach provided a reasonable knowledge of the stellar age and kinematic properties, together with compelling indications that the extended feature is indeed the signature of a high-velocity, or runaway, newborn star. Results. Our main result is the discovery of a low-mass young stellar object that fits the concept of a runaway T-Tauri star that was hypothesized several decades ago. In this peculiar star, nicknamed UJT-1, the interaction of the stellar wind with the surrounding medium becomes extreme. Under reasonable assumptions, this unusual degree of interaction has the potential to encode the mass-loss history of the star on timescales of several $10^5$ years

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J. Martí, P. Luque-Escamilla and E. Sánchez-Ayaso
Mon, 1 May 23
40/51

Comments: Accepted for publication in Astronomy and Astrophysics

A Keplerian disk with a four-arm spiral birthing an episodically accreting high-mass protostar [SSA]

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http://arxiv.org/abs/2304.14740


High-mass protostars (M${\star} >$ 8 M${\odot}$) are thought to gain the majority of their mass via short, intense bursts of growth. This episodic accretion is thought to be facilitated by gravitationally unstable and subsequently inhomogeneous accretion disks. Limitations of observational capabilities, paired with a lack of observed accretion burst events has withheld affirmative confirmation of the association between disk accretion, instability and the accretion burst phenomenon in high-mass protostars. Following its 2019 accretion burst, a heat-wave driven by a burst of radiation propagated outward from the high-mass protostar G358.93-0.03-MM1. Six VLBI (very long baseline interferometry) observations of the raditively pumped 6.7 GHz methanol maser were conducted during this period, tracing ever increasing disk radii as the heat-wave propagated outward. Concatenating the VLBI maps provided a sparsely sampled, milliarcsecond view of the spatio-kinematics of the accretion disk covering a physical range of $\sim$ 50 – 900 AU. We term this observational approach `heat-wave mapping’. We report the discovery of a Keplerian accretion disk with a spatially resolved four-arm spiral pattern around G358.93-0.03-MM1. This result positively implicates disk accretion and spiral arm instabilities into the episodic accretion high-mass star formation paradigm.

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R. Burns, Y. Uno, N. Sakai, et. al.
Mon, 1 May 23
42/51

Comments: Published in Nature Astronomy in 2023

Mind the Gap I: H$α$ Activity of M Dwarfs Near the Partially/Fully Convective Boundary and a New H$α$ Emission Deficiency Zone on the Main Sequence [SSA]

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http://arxiv.org/abs/2304.14452


Since identifying the gap in the H-R Diagram (HRD) marking the transition between partially and fully convective interiors, a unique type of slowly pulsating M dwarf has been proposed. These unstable M dwarfs provide new laboratories in which to understand how changing interior structures result in potentially observable activity at the surface. In this work, we report the results of the largest high-resolution spectroscopic H$\alpha$ emission survey to date spanning this transition region, including 480 M dwarfs observed using the CHIRON spectrograph at CTIO/SMARTS 1.5-m. We find that M dwarfs with H$\alpha$ in emission are almost entirely found 0 to 0.5 magnitude above the top edge of the gap in the HRD, whereas effectively no stars in and below the gap show emission. Thus, the top edge of the gap marks a relatively sharp activity transition and there is no anomalous H$\alpha$ activity for stars in the gap. We also identify a new region at 10.3 $<M_{G}<$ 10.8 on the main sequence where fewer M dwarfs exhibit H$\alpha$ emission compared to M dwarfs above and below this magnitude range. Careful evaluation of literature results indicates that 1) rotation and H$\alpha$ activity distributions on the main sequence are closely related, and 2) fewer stars in this absolute magnitude range rotate in less than $\sim$13 days than populations surrounding this region. This result suggests that the most massive fully convective stars lose their angular momentum faster than both partially convective stars and less massive fully convective stars.

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W. Jao, T. Henry, R. White, et. al.
Mon, 1 May 23
51/51

Comments: 30 pages, 18 figures, and 6 table. Submitted to AJ

Magnetic Field Line Separation by Random Ballistic Decorrelation in Transverse Magnetic Turbulence [SSA]

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http://arxiv.org/abs/2304.14067


The statistics of the magnetic field line separation provide insight into how a bundle of field lines spreads out and the dispersion of non-thermal particles in a turbulent environment, which underlies various astrophysical phenomena. Its diffusive character depends on the distance along the field line, the initial separation, and the characteristics of the magnetic turbulence. This work considers the separation of two magnetic field lines in general transverse turbulence in terms of the magnetic power spectrum in three-dimensional wavenumber space. We apply non-perturbative methods using Corrsin’s hypothesis and assume random ballistic decorrelation to calculate the ensemble average field line separation for general transverse magnetic turbulence. For 2D+slab power spectra, our analytic formulae and computer simulations give similar results, especially at low slab fraction. Our analytical expression also demonstrates several features of field line separation that are verified by computer simulations.

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C. Yannawa, P. Pongkitiwanichakul, D. Ruffolo, et. al.
Fri, 28 Apr 23
9/68

Comments: N/A

Internal calibration of LAMOST and Gaia DR3 GSP-Spec stellar abundances [SSA]

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http://arxiv.org/abs/2304.13951


Stellar chemical abundances are crucial and fundamental in astrophysics. However, they could suffer from substantial systematic errors according to several investigations but still lack calibrations in bulk. By using Gaia wide binaries, we find the temperature-dependent bias between the two binary components for [Fe/H] and [alpha/Fe] measurements from the LAMOST low-resolution spectra and Gaia RVS spectra. At Teff=4000 K, the LAMOST [Fe/H] is significantly underestimated by approximately 0.4 dex, compared with its typical uncertainty of 0.1 dex. Its [alpha/Fe] is overestimated by about 0.2 dex. For Gaia, the underestimation of [M/H] and overestimation of [alpha/Fe] becomes pronounced near 7000 K with smaller magnitudes. We perform an internal calibration by minimizing the differences between binary components and provide the correction curves. After corrections, the standard deviations of the residuals compared to the PASTEL catalog decrease from about 0.045/0.1 to 0.02/0.043 for LAMOST and Gaia, respectively. The chemical homogeneity of the open cluster M 44 is also improved by a factor of two. We stress that the underestimation of [Fe/H] could lead to an overestimation of binary fractions when selecting binary stars by the excess of luminosity. The method of this work could be applied to other data-sets in the future. Our results will benefit statistic studies that use LAMOST and Gaia samples with a wide temperature range.

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Z. Niu, H. Yuan and J. Liu
Fri, 28 Apr 23
12/68

Comments: 13 pages, 7 figure, ApJ accepted, comments are welcome

Tidal Forcing on the Sun and the 11-year Solar Activity Cycle [SSA]

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http://arxiv.org/abs/2304.14168


The hypothesis that tidal forces on the Sun are related to the modulations of the solar-activity cycle has gained increasing attention. The works proposing physical mechanisms of planetary action via tidal forcing have in common that quasi-alignments between Venus, Earth, and Jupiter (V-E-J configurations) would provide a basic periodicity of $\approx 11.0$ years able to synchronize the operation of solar dynamo with these planetary configurations. Nevertheless, the evidence behind this particular tidal forcing is still controversial. In this context we develop, for the first time, the complete Sun’s tide-generating potential (STGP) in terms of a harmonic series, where the effects of different planets on the STGP are clearly separated and identified. We use a modification of the spectral analysis method devised by Kudryavtsev (J. Geodesy. 77, 829, 2004; Astron. Astrophys. 471, 1069, 2007b) that permits to expand any function of planetary coordinates to a harmonic series over long time intervals. We build a catalog of 713 harmonic terms able to represent the STGP with a high degree of precision. We look for tidal forcings related to V-E-J configurations and specifically the existence of periodicities around $11.0$ years.
Although the obtained tidal periods range from $\approx$ 1000 years to 1 week, we do not find any $\approx$ 11.0 years period. The V-E-J configurations do not produce any significant tidal term at this or other periods. The Venus tidal interaction is absent in the 11-year spectral band, which is dominated by Jupiter’s orbital motion. The planet that contributes the most to the STGP in three planets configurations, along with Venus and Earth, is Saturn. An $\approx 11.0$ years tidal period with a direct physical relevance on the 11-year-like solar-activity cycle is highly improbable.

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R. Cionco, S. Kudryavtsev and W. Soon
Fri, 28 Apr 23
23/68

Comments: Accepted (April 2023) to be published in Solar Physics

Sodium enhancement in evolved CVs [SSA]

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http://arxiv.org/abs/2304.13750


We present follow-up spectroscopy of 21 cataclysmic variables (CVs) with evolved secondaries and ongoing or recently-terminated mass transfer. Evolutionary models predict that the secondaries should have anomalous surface abundances owing to nuclear burning in their cores during their main-sequence evolution and subsequent envelope stripping by their companion white dwarfs. To test these models, we measure sodium (Na) abundances of the donors from the Fraunhofer “D” doublet. Accounting for interstellar absorption, we find that {\it all} objects in our sample have enhanced Na abundances. We measure 0.3 $\lesssim$ [Na/H] $\lesssim$ 1.5 dex across the sample, with a median [Na/H] = 0.956 dex, i.e., about an order of magnitude enhancement over solar values. To interpret these values, we run MESA binary evolution models of CVs in which mass transfer begins just as the donor leaves the main sequence. These generically predict Na enhancement in donors with initial donor masses $\gtrsim 1\,M_{\odot}$, consistent with our observations. In the models, Na enrichment occurs in the donors’ cores via the NeNa cycle near the end of their main-sequence evolution. Na-enhanced material is exposed when the binaries reach orbital periods of a few hours. Donors with higher initial masses are predicted to have higher Na abundances at fixed orbital period owing to their higher core temperatures during main-sequence evolution. The observed [Na/H] values are on average $\approx$0.3 dex higher than predicted by the models. Surface abundances of evolved CV donors provide a unique opportunity to study nuclear burning products in the cores of intermediate-mass stars.

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N. Yamaguchi, K. El-Badry, A. Rodriguez, et. al.
Fri, 28 Apr 23
30/68

Comments: N/A

Constraining mass-transfer and common-envelope physics with post-supernova companion monitoring [SSA]

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http://arxiv.org/abs/2304.13864


We present an analytical model that describes the response of companion stars after being impacted by a supernova in a close binary system. This model can be used to constrain the pre-supernova binary properties using photometry of the companion star several years after the explosion in a relatively simple manner. The derived binary parameters are useful in constraining the evolutionary scenario for the progenitors and the physics of binary interactions. We apply our model to the observed photometry of some known stripped-envelope supernova companions (SN1993J, SN2001ig, SN2006jc, SN2011dh, SN2013ge). Combined with other observational constraints such as the pre-supernova progenitor photometry, we find that SN1993J and SN2011dh likely had relatively massive companions on wide orbits, while SN2006jc may have had a relatively low-mass companion on a tight orbit. This trend suggests that type IIb supernova progenitors evolved from stable mass transfer channels and type Ibc progenitors may have formed from common-envelope channels. The constraints on orbital separation helps us probe the highly uncertain common-envelope physics for massive stars, especially with multiple epochs of companion observations.

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R. Hirai
Fri, 28 Apr 23
48/68

Comments: 7 pages, 8 figures. Submitted to MNRAS. Comments welcome

A speckle search for the outer companion of KIC 9832227 [SSA]

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http://arxiv.org/abs/2304.13729


We present Gemini-N/’Alopeke speckle observations of KIC 9832227, a system originally predicted to become a red nova. The diffraction limited observations do not find an outer companion between 11 and 678 AU that could be responsible for the period changes of the system.

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R. Salinas and S. Howell
Fri, 28 Apr 23
50/68

Comments: RNAAS, 7,75

Stellar variability in Gaia DR3. I. Three-band photometric dispersions for 145 million sources [SSA]

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http://arxiv.org/abs/2304.14249


CONTEXT: The unparalleled characteristics of Gaia photometry make it an excellent choice to study stellar variability. AIMS: To measure the phot. dispersion in G+G_BP+G_RP of the 145 677 450 Gaia DR3 5-parameter sources with G <= 17 mag and G_BP-G_RP with -1.0 to 8.0 mag. To use that unbiased sample to analyze stellar variability in the Milky Way, LMC, and SMC. METHODS: We convert from magnitude uncertainties to the observed phot. dispersions, calculate the instrumental component as a function of apparent magnitude and color, and use it to transform the observed dispersions into the astrophysical ones. We give variability indices in the three bands for the whole sample. We use the subsample of Rimoldini et al. that includes light curves and variability types to calibrate our results and establish their limitations. RESULTS: We use information from the MW, LMC, and SMC CAMDs to discuss variability across the HRD. Most WDs and sdBs are variable and follow a distribution in s_G peaking around 12 mmag but variability decreases for the former with age. The MS region in the Gaia CAMD has an s_G distribution peaks at low values (~1-2 mmag) and has a large tail dominated by EBs, RR Lyr stars, and YSOs. RC stars are characterized by little variability, with their s_G distribution peaking at 1 mmag or less. The stars in the PMS region are highly variable, with a power law distribution in s_G with slope 2.75 and a cutoff for values lower than 7 mmag. The luminous red stars region of the Gaia CAMD has the highest variability, with its extreme dominated by AGB stars and with a power law in s_G with a slope of ~2.2 that extends from there to a cutoff of 7 mmag. We show that our method can be used to search for LMC Cepheids. We analyze four stellar clusters with O stars and detect a strong difference in s_G between stars that are already in the MS and those that are still in the PMS. [ABRIDGED]

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J. Apellániz, G. Holgado, M. González, et. al.
Fri, 28 Apr 23
59/68

Comments: Submitted to A&A. Comments welcome

Spectropolarimetric investigation of magnetohydrodynamic wave modes in the photosphere: First results from PHI on board Solar Orbiter [SSA]

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http://arxiv.org/abs/2304.14155


In November 2021, Solar Orbiter started its nominal mission phase. The remote-sensing instruments on board the spacecraft acquired scientific data during three observing windows surrounding the perihelion of the first orbit of this phase. The aim of the analysis is the detection of magnetohydrodynamic (MHD) wave modes in an active region by exploiting the capabilities of spectropolarimetric measurements. The High Resolution Telescope (HRT) of the Polarimetric and Helioseismic Imager (SO/PHI) on board the Solar Orbiter acquired a high-cadence data set of an active region. This is studied in the paper. B-$\omega$ and phase-difference analyses are applied on line-of-sight velocity and circular polarization maps and other averaged quantities. We find that several MHD modes at different frequencies are excited in all analysed structures. The leading sunspot shows a linear dependence of the phase lag on the angle between the magnetic field and the line of sight of the observer in its penumbra. The magnetic pore exhibits global resonances at several frequencies, which are also excited by different wave modes. The SO/PHI measurements clearly confirm the presence of magnetic and velocity oscillations that are compatible with one or more MHD wave modes in pores and a sunspot. Improvements in modelling are still necessary to interpret the relation between the fluctuations of different diagnostics.

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D. Calchetti, M. Stangalini, S. Jafarzadeh, et. al.
Fri, 28 Apr 23
63/68

Comments: N/A

An enigma of Przybylski's star: is there promethium on its surface? [SSA]

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http://arxiv.org/abs/2304.13623


We carried out a new attempt to check for the presence promethium lines in the spectrum of HD101065 (Przybylski’s star). The neutron capture element promethium does not have stable isotopes and the maximum half-life time is about 18 years. Thus its presence in this peculiar star would indicate an ongoing process of irradiation of its surface layers with free neutrons. Unfortunately, almost all promethium lines are heavily blended with lines of other neutron capture elements and other species. We selected and analysed three lines of promethium (Pm I and Pm II) and came to the conclusion that at present it is impossible to definitely claim the presence of this element in Przybylski’s star atmosphere.

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S. Andrievsky, S. Korotin, K. Werner, et. al.
Thu, 27 Apr 23
5/78

Comments: Accepted for publication in Astronomische Nachrichten

The Initiation Mechanism of the First On-disk X-Class Flare of Solar Cycle 25 [SSA]

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http://arxiv.org/abs/2304.13241


In this paper we study the initiation mechanism of the first on-disk X-class eruptive flare in solar cycle 25. Coronal magnetic field reconstructions reveal a magnetic flux rope (MFR) with configuration highly consistent with a filament existing for a long period before the flare, and the eruption of the whole filament indicates that the MFR erupted during the flare. However, quantitative analysis shows that the pre-flare MFR resides in a height too low to trigger a torus instability (TI). The filament experienced a slow rise before the flare onset, for which we estimate evolution of the filament height using a triangulation method by combining the SDO and STEREO observations, and find it is also much lower than the critical height for triggering TI. On the other hand, the pre-flare evolution of the current density shows progressive thinning of a vertical current layer on top of the flare PIL, which suggests that a vertical current sheet forms before the eruption. Meanwhile, there is continuously shearing motion along the PIL under the main branch of the filament, which can drive the coronal field to form such a current sheet. As such, we suggest that the event follows a reconnection-based initiation mechanism as recently established using a high-accuracy MHD simulation, in which an eruption is initiated by reconnection in a current sheet that forms gradually within continuously-sheared magnetic arcade. The eruption should be further driven by TI as the filament quickly rises into the TI domain during the eruption.

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A. Duan, C. Jiang, Z. Zhou, et. al.
Thu, 27 Apr 23
8/78

Comments: N/A

A Statistical Investigation of Decayless Oscillations in Small-scale Coronal Loops Observed by Solar Orbiter/EUI [SSA]

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http://arxiv.org/abs/2304.13554


Decayless kink oscillations are omnipresent in the solar atmosphere and a viable candidate for coronal heating. Though there have been extensive studies of decayless oscillations in coronal loops with a few hundred Mm lengths, the properties of these oscillations in small-scale ($\sim$10 Mm) loops are yet to be explored. In this study, we present the properties of decayless oscillations in small loops embedded in the quiet corona and coronal holes. We use high resolution observations from the Extreme Ultraviolet Imager onboard Solar Orbiter with pixel scales of 210 km and 5 s cadence or better. We find 42 oscillations in 33 coronal loops with loop lengths varying between 3 to 23 Mm. The average displacement amplitude is found to be 136 km. The oscillations period has a range of 27 to 276 s, and the velocity amplitudes range from 2.2 to 19.3 km s$^{-1}$. The observed kink speeds are lower than those observed in active region coronal loops. The variation of loop length with the period does not indicate a strong correlation. Coronal seismology technique indicated an average magnetic field value of 2.1 G. We estimate the energy flux with a broad range of 0.6-314 W m$^{-2}$. Moreover, we note that the short-period decayless oscillations are not prevalent in the quiet Sun and coronal holes. Therefore, our study suggests that decayless oscillations in small-scale coronal loops are unlikely to provide enough energy to heat the quiet Sun and accelerate solar wind in the coronal holes.

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A. Shrivastav, V. Pant, D. Berghmans, et. al.
Thu, 27 Apr 23
9/78

Comments: Submitted to Astronomy & Astrophysics. Comments are welcome

Infrared spectroscopy of the 2022 eruption of the recurrent nova U Sco [SSA]

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http://arxiv.org/abs/2304.13508


We present near-infrared spectroscopy of the 2022 eruption of the recurrent nova U Sco, over the period from 5.2 to 45.4 days after outburst. This is the most intensive infrared study of this nova. Our observations started early after the outburst and extended almost to the end of the “Super Soft” X-ray phase. A major find is the presence of coronal lines from day 9.41, one of the earliest appearances of these in any nova, classical or recurrent. The temperature of the coronal gas is $7\times10^5$ K. There is also evidence for the presence of much cooler ($\lesssim2.5\times10^4$ K) gas. Remarkable changes are seen in the HeI $1.083\mu$m line, the strength of which declines, then recovers, in anti-correlation with the X-ray behaviour. We conclude that shock ionisation is the dominant excitation mechanism for the coronal line emission. There is evidence in the infrared spectra for the presence of black body emission at $\sim20000$ K, which we tentatively identify with the irradiated secondary, and for free-free/free-bound emission. For the previously determined binary inclination of $82.7$ degrees, the implied ejection velocities are as high as 22000 km s$^{-1}$. These velocities appear unprecedented in nova outflows, and are comparable to those seen in supernovae, thereby marking U Sco as a truly remarkable object.

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A. Evans, D. Banerjee, C. Woodward, et. al.
Thu, 27 Apr 23
10/78

Comments: Accepted for publication in MNRAS

A study of the propagation of magnetoacoustic waves in small-scale magnetic fields using solar photospheric and chromospheric Dopplergrams: HMI/SDO and MAST observations [SSA]

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http://arxiv.org/abs/2304.13492


In this work, we present a study of the propagation of low-frequency magneto-acoustic waves into the solar chromosphere within small-scale inclined magnetic fields over a quiet-magnetic network region utilizing near-simultaneous photospheric and chromospheric Dopplergrams obtained from the HMI instrument onboard SDO spacecraft and the Multi-Application Solar Telescope (MAST) operational at the Udaipur Solar Observatory, respectively. Acoustic waves are stochastically excited inside the convection zone of the Sun and intermittently interact with the background magnetic fields resulting into episodic signals. In order to detect these episodic signals, we apply the wavelet transform technique to the photospheric and chromospheric velocity oscillations in magnetic network regions. The wavelet power spectrum over photospheric and chromospheric velocity signals show a one-to-one correspondence between the presence of power in the 2.5-4 mHz band. Further, we notice that power in the 2.5-4 mHz band is not consistently present in the chromospheric wavelet power spectrum despite its presence in the photospheric wavelet power spectrum. This indicates that leakage of photospheric oscillations (2.5-4 mHz band) into the higher atmosphere is not a continuous process. The average phase and coherence spectra estimated from these photospheric and chromospheric velocity oscillations illustrate the propagation of photospheric oscillations (2.5-4 mHz) into the solar chromosphere along the inclined magnetic fields. Additionally, chromospheric power maps estimated from the MAST Dopplergrams also show the presence of high-frequency acoustic halos around relatively high magnetic concentrations, depicting the refraction of high-frequency fast mode waves around vA ~ vs layer in the solar atmosphere.

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H. Kumar, B. Kumar, S. Rajaguru, et. al.
Thu, 27 Apr 23
12/78

Comments: 16 pages, 7 figures, Accepted for Publication in Journal of Atmospheric and Solar-Terrestrial Physics (Special Issue of STP-15)

SDSS J094002.56+274942.0: an SU UMa star with an orbital period of 3.92 hours and an apparently unevolved secondary [SSA]

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http://arxiv.org/abs/2304.13311


We found that SDSS J094002.56+274942.0 underwent a superoutburst in 2019 February based on our observations and Zwicky Transient Facility (ZTF) data. This object showed shallow eclipses during this superoutburst and we established the orbital period to be 0.1635015(1) d in combination with the ZTF and Asteroid Terrestrial-impact Last Alert System (ATLAS) data in quiescence. Superhumps apparently started to develop soon after the object reached the plateau phase and fully grown superhumps were recorded within the initial 6 d of the plateau phase. Using the superhump and orbital periods, we obtained a mass ratio (q) of 0.39(3) and obtained an inclination of 70.5(5) deg by eclipse modeling. These values reproduced the quiescent ellipsoidal variations very well. Using the Gaia parallax and 2MASS observations, we confirmed that the secondary is indistinguishable from an unevolved main-sequence star. The resultant mass ratio and orbital period were the highest among SU UMa stars, and this provided a proof that the 3:1 resonance can develop in less than 6 d even in q=0.39(3). The superoutburst faded relatively rapidly and was followed by a rebrightening, suggesting that the tidal effect in a large-q system was insufficient to maintain a long superoutburst and the remnant matter caused a rebrightening. The presence of such a system among dwarf novae is against the conventional idea that outbursts in dwarf novae are not long enough to develop superhumps, in contrast to novalike variables, under a weak tidal effect. The present observation also supports that the 3:1 resonance is the cause of a long outburst, and not its consequence, even under extreme q. The rapid growth of the 3:1 resonance in a high-q system challenges the generally accepted results of hydrodynamic simulations.

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T. Kato and T. Vanmunster
Thu, 27 Apr 23
13/78

Comments: 17 pages, 7 figures, VSOLJ Variable Star Bulletin No. 114

Which Component of Solar Magnetic Field Drives the Evolution of Interplanetary Magnetic Field over Solar Cycle? [SSA]

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http://arxiv.org/abs/2304.13347


The solar magnetic structure changes over the solar cycle. It has a dipole structure during solar minimum, where the open flux extends mainly from the polar regions into the interplanetary space. During maximum, a complex structure is formed with low-latitude active regions and weakened polar fields, resulting in spread open field regions. However, the components of the solar magnetic field that is responsible for long-term variations in the interplanetary magnetic field (IMF) are not clear, and the IMF strength estimated based on the solar magnetic field is known to be underestimated by a factor of 3 to 4 against the actual in-situ observations (the open flux problem). To this end, we decomposed the coronal magnetic field into the components of the spherical harmonic function of degree and order $(\ell, m)$ using the potential field source surface model with synoptic maps from SDO/HMI for 2010 to 2021. As a result, we found that the IMF rapidly increased in December 2014 (seven months after the solar maximum), which coincided with the increase in the equatorial dipole, $(\ell, m)=(1, \pm1)$, corresponding to the diffusion of active regions toward the poles and in the longitudinal direction. The IMF gradually decreased until December 2019 (solar minimum) and its variation corresponded to that of the non-dipole component $\ell\geq2$. Our results suggest that the understanding of the open flux problem may be improved by focusing on the equatorial dipole and the non-dipole component and that the influence of the polar magnetic field is less significant.

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M. Yoshida, T. Shimizu and S. Toriumi
Thu, 27 Apr 23
28/78

Comments: 19 pages, 9 figures, accepted for publication in ApJ

Exploring magnetic field properties at the boundary of solar pores: A comparative study based on SDO-HMI observations [SSA]

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http://arxiv.org/abs/2304.13212


The Sun’s magnetic fields play an important role in various solar phenomena. Solar pores are regions of intensified magnetic field strength compared to the surrounding photospheric environment, and their study can help us better understand the properties and behaviour of magnetic fields in the Sun. Up to now, there exists only a single study on magnetic field properties at the boundary region of a pore. Therefore, the main goal of this work is to increase the statistics of magnetic properties determining the pore boundary region. We analyse six solar pores using data from the Helioseismic and Magnetic Imager instrument on board the Solar Dynamics Observatory. We apply image processing techniques to extract the relevant features of the solar pores and determine the boundary conditions of the magnetic fields. We find the maximal vertical magnetic field values on the boundaries of the studied solar pores to range from 1400~G to 1600~G, with a standard deviation between 7.8\% and 14.8\%. These values are lower than those reported in the mentioned preceding study. However, this can be explained by differences in spatial resolution as well as the type of data we used. The vertical magnetic field is an important factor in determining the boundary of solar pores, and it plays a more relevant role than the intensity gradient. The obtained information will be useful for future studies on the formation and evolution of magnetic structures of the Sun. Additionally, this study highlights the importance of high spatial resolution data for the purpose of accurately characterising the magnetic properties of solar pores.

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J. Rozo, S. Domínguez, D. Utz, et. al.
Thu, 27 Apr 23
29/78

Comments: 9 pages, 7 figures. Accepted for publication in Astronomy and Astrophysics (A&A)

Simulations of Protoplanetary Disk Dispersal: Stellar Mass Dependence of the Disk Lifetime [SSA]

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http://arxiv.org/abs/2304.13316


Recent infrared and submillimeter observations suggest that the protoplanetary disk lifetime depends on the central stellar mass. The disk dispersal is thought to be driven by viscous accretion, magneto-hydrodynamics (MHD) winds, and photoevaporation by the central star. We perform a set of one-dimensional simulations of long-term disk evolution that include all the three processes. We vary the stellar mass in the range of 0.5-7M${\odot}$, and study the mass dependence of the disk evolution. We show that a significant fraction of the disk gas is lost by MHD winds in the early stage, but the later disk evolution is mainly governed by photoevaporation. The disk radius decreases as photoevaporation clears out the gas in the outer disk efficiently. The qualitative evolutionary trends of the disk mass are remarkably similar for the wide range of the central stellar mass we consider, and the time evolution of the disk mass can be well fitted by a simple function. The dispersal time is approximately ten million years for low mass stars with weak mass dependence, but gets as short as two million years around a 7M${\odot}$ star. In the latter case, a prominent inner hole is formed by the combined effect of accretion and MHD winds within about one million years. The strength of the MHD wind and viscous accretion controls the overall mass-loss rate, but does not alter the dependence of the dispersal timescale on the central stellar mass.

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A. Komaki, S. Fukuhara, T. Suzuki, et. al.
Thu, 27 Apr 23
38/78

Comments: 14 pages, 10 figures, 1 table

FU Orionis disk outburst: evidence for a gravitational instability scenario triggered in a magnetically dead zone [SSA]

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http://arxiv.org/abs/2304.13414


Context: FUors outbursts are a crucial stage of accretion in young stars. However a complete mechanism at the origin of the outburst still remains missing. Aims: We aim at constraining the instability mechanism in FU Orionis star itself, by directly probing the size and the evolution in time of the outburst region with near-infrared interferometry, and to confront it to physical models of this region. Methods: FU Orionis has been a regular target of near-infrared interferometry. In this paper, we analyze more than 20 years of interferometric observations to perform a temporal monitoring of the region of the outburst, and compare it to the spatial structure deduced from 1D MHD simulations. Results: We measure from the interferometric observations that the size variation of the outburst region is compatible with a constant or slightly decreasing size over time in the H and K band. The temporal variation and the mean sizes are consistently reproduced by our 1D MHD simulations. We find that the most compatible scenario is a model of an outburst occurring in a magnetically layered disk, where a Magneto-Rotational Instability (MRI) is triggered by a Gravitational Instability (GI) at the outer edge of a dead-zone. The scenario of a pure Thermal Instability (TI) fails to reproduce our interferometric sizes since it can only be sustained in a very compact zone of the disk <0.1 AU. The scenario of MRI-GI could be compatible with an external perturbation enhancing the GI, such as tidal interactions with a stellar companion, or a planet at the outer edge of the dead-zone. Conclusions: The layered disk model driven by MRI turbulence is favored to interpret the spatial structure and temporal evolution of FU Orionis outburst region. Understanding this phase gives a crucial link between the early phase of disk evolution and the process of planet formation in the first inner AUs.

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G. Bourdarot, J. Berger, G. Lesur, et. al.
Thu, 27 Apr 23
51/78

Comments: Accepted for publication in A&A

A low-metallicity massive contact binary undergoing slow Case A mass transfer: A detailed spectroscopic and orbital analysis of SSN 7 in NGC 346 in the SMC [SSA]

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http://arxiv.org/abs/2304.13720


Most massive stars are believed to be born in close binary systems where they can exchange mass, which impacts the evolution of both binary components. Their evolution is of great interest in the search for the progenitors of gravitational waves. However, there are unknowns in the physics of mass transfer as observational examples are rare, especially at low metallicity. Nearby low-metallicity environments are particularly interesting hunting grounds for interacting systems as they act as the closest proxy for the early universe where we can resolve individual stars. Using multi-epoch spectroscopic data, we complete a consistent spectral and orbital analysis of the early-type massive binary SSN~7 hosting a ON3\,If$^\ast$+O5.5\,V((f)) star. Using these detailed results, we constrain an evolutionary scenario that can help us to understand binary evolution in low metallicity.} We were able to derive reliable radial velocities of the two components from the multi-epoch data, which were used to constrain the orbital parameters. The spectroscopic data covers the UV, optical, and near-IR, allowing a consistent analysis with the stellar atmosphere code, PoWR. Given the stellar and orbital parameters, we interpreted the results using binary evolutionary models. The two stars in the system have comparable luminosities of ${\log (L_1/L_{\odot}) = 5.75}$ and ${\log (L_2/L_{\odot}) = 5.78}$ for the primary and secondary, respectively, but have different temperatures (${T_1=43.6\,\mathrm{kK}}$ and ${T_2=38.7\,\mathrm{kK}}$). The primary ($32\,M_{\odot}$) is less massive than the secondary ($55\,M_{\odot}$), suggesting mass exchange. The mass estimates are confirmed by the orbital analysis. The revisited orbital period is $3\,\mathrm{d}$. Our evolutionary models also predict mass exchange. Currently, the system is a contact binary undergoing a slow Case A phase, making it the most massive [Abridged]

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M. Rickard and D. Pauli
Thu, 27 Apr 23
60/78

Comments: 20 pages

EI Eridani: a star under the influence — The effect of magnetic activity in the short and long term [SSA]

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http://arxiv.org/abs/2304.13234


We use our photometric time series of more than forty years to analyze the long-term behaviour of EI Eri. Flare activity is investigated using space-borne photometric data obtained with TESS. The MUSICOS campaign aimed to achieve high-resolution spectroscopic observations from many sites around the globe, so that uninterrupted phase coverage of EI Eri became available. We use these data to reconstruct successive surface temperature maps of the star in order to study the changes of starspots on a very short timescale.
We use long-term, seasonal period analysis of our photometric time series to study changes in the rotational period. Short-term Fourier-transform is also applied to look for activity cycle-like changes. We also study the phase and frequency distribution of hand-selected flares. We apply our multi-line Doppler imaging code to reconstruct four consecutive Doppler images. These images are also used to measure surface differential rotation by our cross-correlation technique. In addition, we carry out tests to demonstrate how Doppler imaging is affected by the fact that the data came from several different instruments with different spectral resolutions.
Seasonal period analysis of the light curve reveals a smooth, significant change in period, possibly indicating the evolution of active latitudes. Temperature curves from $B-V$ and $V-I$ show slight differences, indicating the activity of EI Eri is spot dominated. Short-term Fourier transform reveals smoothly changing cycles between 4.5–5.5 and 8.9–11.6 years. The time-resolved spotted surface of EI Eri from Doppler imaging enabled us to follow the evolution of the different surface features. Cross-correlating the consecutive Doppler maps reveal surface shear of $\alpha=0.036\pm0.007$. Our tests validate our approach and show that the surface temperature distribution is adequately reconstructed by our method.

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L. Kriskovics, Z. Kővári, B. Seli, et. al.
Thu, 27 Apr 23
64/78

Comments: 14 pages, 13 figures, A&A accepted

Relativistic Corrections in White Dwarf Asteroseismology [SSA]

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http://arxiv.org/abs/2304.13055


With the precision now afforded by modern space-based photometric observations from the retired K2 and current TESS missions, the effects of general relativity (GR) may be detectable in the light curves of pulsating white dwarfs (WDs). Almost all WD models are calculated using a Newtonian description of gravity and hydrodynamics. To determine if inclusion of GR leads to observable effects, we used idealized models of compact stars and made side-by-side comparison of mode periods computed using a (i) Newtonian and (ii) GR description of the equilibrium structure and nonradial pulsations. For application to white dwarfs, it is only necessary to include the first post-Newtonian (1PN) approximation to GR. The mathematical nature of the linear nonradial pulsation problem is then qualitatively unchanged and the GR corrections can be written as extensions of the classic Dziembowski equations. As such, GR effects might easily be included in existing asteroseismology codes. The idealized stellar models are (i) \pn1 relativistic polytropes and (ii) stars with cold degenerate-electron equation of state featuring a near-surface chemical transition from $\mu_e = 2$ to $\mu_e = 1$, simulating a surface hydrogen layer. Comparison of Newtonian and 1PN normal mode periods reveals fractional differences on the order of the surface gravitational redshift $z$. For a typical WD, this fractional difference is $\sim 10^{-4}$ and is greater than the period uncertainty $\sigma_{\Pi}/\Pi$ of many white dwarf pulsation modes observed by TESS. A consistent theoretical modeling of periods observed in these stars should in principle include GR effects to 1PN order.

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S. Boston, C. Evans and J. Clemens
Thu, 27 Apr 23
71/78

Comments: N/A

Record-breaking polarization from the interacting superluminous supernova 2017hcc [SSA]

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http://arxiv.org/abs/2304.12368


We present multiepoch spectropolarimetry of the superluminous interacting Type IIn supernova SN2017hcc, covering 16 to 391 days after explosion. In our first epoch we measure continuum polarization as high as 6%, making SN 2017hcc the most intrinsically polarized SN ever reported. During the first 29 days of coverage, when the polarization is strongest, the continuum polarization has a wavelength dependence that rises toward blue wavelengths, and becomes wavelength independent by day 45. The polarization strength drops rapidly during the first month, even as the SN flux is still climbing to peak brightness. Nonetheless, record-high polarization is maintained until day 68, at which point the source polarization declines to 1.9%, comparable to peak levels in previous well-studied SNe IIn. Thereafter the SN continues in polarization decline, while exhibiting only minor changes in position angle on the sky. The blue slope of the polarized continuum during the first month, accompanied by short-lived polarized flux for Balmer emission, suggests that an aspherical distribution of dust grains in pre-shock circumstellar material (CSM) is echoing the SN IIn spectrum and strongly influencing the polarization, while the subsequent decline during the wavelength-independent phase appears broadly consistent with electron scattering near the SN/CSM interface. The persistence of the polarization position angle between these two phases suggests that the pre-existing CSM responsible for the dust scattering at early times is part of the same geometric structure as the electron-scattering region that dominates the polarization at later times. SN2017hcc appears to be yet another, but much more extreme, case of aspherical yet well-ordered CSM in Type IIn SNe, possibly resulting from pre-SN mass loss shaped by a binary progenitor system.

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J. Mauerhan, N. Smith, G. Williams, et. al.
Wed, 26 Apr 23
6/62

Comments: Submitted to MNRAS April 21, 2023

Variable stars detection in the field of open cluster NGC 188 [SSA]

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http://arxiv.org/abs/2304.12738


This work presents the charge-coupled device (CCD) photometric survey of the old open cluster NGC 188. Time-series V-band photometric observations were conducted for ten nights in January 2017 using the Nanshan One-meter Wide-field Telescope (NOWT) to search for variable stars in the field of the cluster field. A total of 25 variable stars, including one new variable star, were detected in the target field. Among the detected variables, 16 are cluster member stars, and the others are identified as field stars. The periods, radial velocities, effective temperatures, and classifications of the detected variables are discussed in this work. Most of the stars’ effective temperatures are between 4200 K and 6600 K, indicating their spectral types are G or K. The newly discovered variable is probably a W UMa system. In this study, a known cluster variable star (V21 = V0769 Cep) is classified as an EA-type variable star based on the presence of an 0.5 magnitude eclipse in its light curve.

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F. Song, H. Niu, A. Esamdin, et. al.
Wed, 26 Apr 23
19/62

Comments: N/A

An evolutionary model for V404 Cyg system [SSA]

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http://arxiv.org/abs/2304.12894


V404 Cyg is a Low Mass X-Ray Binary (LMXB) system that has undergone outbursts in 1938, 1989, and 2015. During these events, it has been possible to determine relevant data of the system; such as the masses of the compact object (a black hole, BH) and its companion, the orbital period, the companion spectral type, and luminosity class, among others. Remarkably, the companion star has a metallicity appreciably higher than solar. All these data allow us to construct theoretical models to account for its structure, looking for its initial configuration and predicting its final fate. Assuming that the BH is already formed when the primary star reaches the Zero Age Main Sequence, we used our binary evolution code for such a purpose. We obtained that the present characteristics of the system are nicely accounted for by a model with initial masses of 9 solar masses for the BH, 1.5 solar masses for the companion star, an initial orbital period of 1.5 d and considering that at most 30% of the mass transferred by the donor is accreted by the BH. The metallicity of the donor for our best fit was Z = 0.028 (twice solar metallicity). We also studied the evolution of the BH spin parameter assuming that initially, it is not rotating. Remarkably, the spin of the BHs in our models is far from reaching the available observational determination. This may indicate that the BH in V404 Cyg is initially spinning, a result that may be relevant for understanding the formation BHs in the context of LMXB systems.

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L. Koninckx, M. Vito and O. Benvenuto
Wed, 26 Apr 23
21/62

Comments: 10 pages, 12 figures

Sparse logistic regression for RR Lyrae vs binaries classification [SSA]

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http://arxiv.org/abs/2304.12355


RR Lyrae (RRL) are old, low-mass radially pulsating variable stars in their core helium burning phase. They are popular stellar tracers and primary distance indicators, since they obey to well defined period-luminosity relations in the near-infrared regime. Their photometric identification is not trivial, indeed, RRL samples can be contaminated by eclipsing binaries, especially in large datasets produced by fully automatic pipelines. Interpretable machine-learning approaches for separating eclipsing binaries from RRL are thus needed. Ideally, they should be able to achieve high precision in identifying RRL while generalizing to new data from different instruments. In this paper, we train a simple logistic regression classifier on Catalina Sky Survey (CSS) light curves. It achieves a precision of 87% at 78% recall for the RRL class on unseen CSS light curves. It generalizes on out-of-sample data (ASAS/ASAS-SN light curves) with a precision of 85% at 96% recall. We also considered a L1-regularized version of our classifier, which reaches 90% sparsity in the light-curve features with a limited trade-off in accuracy on our CSS validation set and — remarkably — also on the ASAS/ASAS-SN light curve test set. Logistic regression is natively interpretable, and regularization allows us to point out the parts of the light curves that matter the most in classification. We thus achieved both good generalization and full interpretability.

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P. Trevisan, M. Pasquato, G. Carenini, et. al.
Wed, 26 Apr 23
31/62

Comments: To appear on The Astrophysical Journal. 13 pages, 8 figures, 3 tables

Testing angular momentum transport processes with asteroseismology of solar-type main-sequence stars [SSA]

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http://arxiv.org/abs/2304.12942


Asteroseismology has become a powerful tool to study the internal rotation of stars, and its study allows to constrain the internal AM transport processes and better understand their physical nature. In this context, we compared the rotation rates predicted by asteroseismology and by starspots measurements for four main-sequence stars from the Kepler LEGACY sample, considering different AM transport prescriptions, and investigated if some of these prescriptions could be ruled out.
We decoupled the modelling of the structure and of the rotational profile, respectively obtained by an asteroseismic characterization and by using rotating models including a detailed treatment of the AM transport. We then compared the mean asteroseismic rotation rate with the surface rotation rate from starspots measurements for each of the AM transport prescriptions. In the hotter part of the HRD (M > ~ 1.2Msun), combining asteroseismic constraints from splittings of pressure modes and surface rotation rates does not allow to conclude on the need for an efficient AM transport in addition to the sole transport by meridional circulation and shear instability. Both prescriptions are indeed consistent with the quasi-solid rotation measured by Benomar et al. (2015) and Nielsen et al. (2017). In the colder part of the HRD, the situation is different due to the efficient braking of the stellar surface by magnetised winds. We find a clear disagreement between the rotational properties of models including only hydrodynamic processes and asteroseismic constraints, while models with magnetic fields correctly reproduce the observations, similarly to the solar case.
This shows the existence of a mass regime corresponding to main-sequence stars around ~ 6000 – 6200 K for which it is difficult to constrain the AM transport processes, unlike for hotter, Gamma Dor stars or colder, less massive solar analogs.

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J. Bétrisey, P. Eggenberger, G. Buldgen, et. al.
Wed, 26 Apr 23
35/62

Comments: Accepted for publication as a Letter in Astronomy and Astrophysics, section 1. Letters to the Editor

Unambiguous Detection of Doubly-Ionized Thorium in the Extreme Ap Star CPD-62 2717 [SSA]

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http://arxiv.org/abs/2304.12938


Despite the universe containing primordial thorium (Th) of sufficient abundance to appear in stellar spectra, detection of Th has to date been tentative and based on just a few weak and blended lines. Here, we present convincing evidence not only for the first Th detection in a magnetic chemically peculiar Ap star but also for the first detection of Th III in a stellar spectrum. CPD-62 2717 was initially recognized as a highly-magnetized Ap star thanks to resolved magnetically split lines captured in $H$-band spectra from the SDSS/APOGEE survey. The star was subsequently pinpointed as extraordinarily peculiar when careful inspection of the $H$-band line content revealed the presence of five lines of Th III, none of which are detected in the other $\sim1500$ APOGEE-observed Ap stars. Follow-up with the VLT+UVES confirmed a similarly peculiar optical spectrum featuring dozens of Th III lines, among other peculiarities. Unlike past claims of Th detection, and owing to high-resolution observations of the strong ($\sim$8$-$12$\,$kG) magnetic field of CPD-62 2717, the detection of Th III can in this case be supported by matches between the observed and theoretical magnetic splitting patterns. Comparison of CPD-62 2717 to stars for which Th overabundances have been previously reported (e.g., Przybylski’s Star) indicate that only for CPD-62 2717 is the Th detection certain. Along with the focus on Th III, we use time series measurements of the magnetic field modulus to constrain the rotation period of CPD-62 2717 to $\sim$4.8 years, thus establishing it as a new example of a super-slowly-rotating Ap star.

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S. Chojnowski, S. Hubrig, D. Nidever, et. al.
Wed, 26 Apr 23
38/62

Comments: N/A

Study of the bipolar jet of the YSO Th 28 with VLT/SINFONI: Jet morphology and H$_2$ emission [SSA]

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http://arxiv.org/abs/2304.12974


$Context.$ The YSO Th 28 possesses a highly collimated jet, which clearly exhibits an asymmetric brightness of its jet lobes at optical and NIR wavelengths. There may be asymmetry in the jet plasma parameters in opposite jet lobes (e.g. electron density, temperature, and outflow velocity). $Aims.$ We examined the Th 28 jet in a 3″x3″ where the jet material is collimated and accelerated. Our goal is to map the morphology and determine its physical parameters to determine the physical origin of such asymmetries. $Methods.$ We present $JHK$-spectra of Th 28 obtained with the SINFONI on the (VLT, ESO) in June-July 2015. $Results.$ The [Fe II] emission originates in collimated jet lobes. Two new axial knots are detected at 1″ in the blue lobe and 1″.2 in the red lobe. The H$_2$ radiation is emitted from an extended region with a radius of $\gtrsim270$ au, which is perpendicular to the jet. The PV diagrams of the bright H$_2$ lines reveal faint H$_2$ emission along both jet lobes as well. The compact and faint H I emission (Pa$\beta$ and Br$\gamma$) comes from two regions, namely from a spherical region around the star and from the jet lobes. The size of the jet launching region is derived as 0″.015 ($\sim$3 au at 185 pc), and the initial opening angle of the Th 28 jet is $\sim28^0$, which makes this jet substantially less collimated than most jets from other CTTs. $Conclusions.$ The emission in [Fe II], H$_2$, and H I lines suggests a morphology in which the ionised gas in the disc appears to be disrupted by the jet. The resolved disc-like H$_2$ emission most likely arises in the disc atmosphere from shocks caused by a radial uncollimated wind. The asymmetry of the [Fe II] photocentre shifts with respect to the jet source arises in the immediate vicinity of the driving source of Th28 and suggests that the observed brightness asymmetry is intrinsic as well.

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S. Melnikov, P. Boley, N. Nikonova, et. al.
Wed, 26 Apr 23
60/62

Comments: 18 pages, 14 figures

Imaging Preflare Broadband Pulsations in the Decimetric-metric Wavelengths [SSA]

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http://arxiv.org/abs/2304.11785


Preflare activities contain critical information about the pre-cursors and causes of solar eruptions. Here we investigate the characteristics and origin of a group of broadband pulsations (BBPs) in the decimetric-metric wavelengths, taking place during the preflare stage of the M7.1 flare dated on 2011 September 24. The event was recorded by multiple solar instruments including the Nan\c{c}ay Radioheliograh that measure the properties of the radio source. The BBPs start $\sim$24 min before the flare onset, extending from $<$ 360 to above 800 MHz with no discernible spectral drift. The BBPs consist of two stages, during the first stage the main source remains stationary, during the second stage it moves outward along with a steepening extreme-ultraviolet (EUV) wave driven by the eruption of a high-temperature structure. In both stages, we observe frequent EUV brightenings and jets originating from the flare region. During the second stage, the BBPs become denser in number and stronger in general, with the level of the polarization increasing gradually from $<$ 20% to $>$ 60% in the right-handed sense. These observations indicate the steepening EUV wave is important to the BBPs during the second stage, while the preflare reconnections causing the jets and EUV brightenings are important in both stages. This is the first time such a strong association of an EUV wave with BBPs is reported. We suggest a reconnection plus shock-sweeping-across-loop scenario for the cause of the BBPs.

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M. Lv, B. Tan, R. Zheng, et. al.
Tue, 25 Apr 23
3/72

Comments: 17 pages, 7 figures

XMM-Newton observation of V1504 Cyg as a probe for the existence of an evaporated corona [SSA]

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http://arxiv.org/abs/2304.11162


AIMS: We present an analysis of an XMM-Newton observation of the dwarf novae V1504 Cyg during the decline from an outburst. Our goal is to search for evidence for an evaporated X-ray corona. Such a corona can be understood as an optically thin geometrically thick disc around a central part of an optically thick geometrically thin disc. METHODS: We study the X-ray spectra using a cooling flow model and the evolution of the amplitude of variability and power density spectra in UV and X-rays. RESULTS: The X-ray (pn) count rate increases from initially around 0.03 cps to 0.17 cps with a harder spectrum and a higher degree of variability. Meanwhile, the OM/UVW1 light curve follows a slow decline with decreasing amplitude of variability. For further study we split the X-ray data into two parts, and analysed them separately. Both parts are described by a cooling flow model, while the first low luminosity part requires an additional power law component suggesting presence of a wind. Spectral fitting revealed a higher temperature during the second brighter part. Timing analysis reveals a potential break frequency at log(f/Hz) = -3.02 during decline towards the quiescence. This detection agrees with optical data from Kepler observations. CONCLUSIONS: The X-ray nature of the break frequency supports the innermost parts of the disc as source of the variability. Moreover, a similar frequency was observed in several other cataclysmic variables and a sandwich model where a geometrically thick corona surrounds the geometrically thin disc is a possible accretion configuration.

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A. Dobrotka, J. Ness, A. Nucita, et. al.
Tue, 25 Apr 23
8/72

Comments: Accepted for publication in Astronomy and Astrophysics

Confinedness of an X3.1 class solar flare occurred in NOAA 12192: Analysis from multi-instruments observations [SSA]

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http://arxiv.org/abs/2304.12156


The non-association of coronal mass ejections with high energetic flares is sparse. For this reason, the magnetic conditions required for the confinedness of major flares is a topic of active research. Using multi-instrument observations, we investigated the evolution and effects of confinedness in an X3.1 flare, which occurred in active region (AR) 12192. The decrease of net fluxes in the brightening regions, near the footpoints of the multi-sigmoidal AR in photosphere and chromosphere, indicative of flux cancellation favouring tether-cutting reconnection (TCR), is observed using the magnetic field observations of HMI/SDO and SOT/Hinode, respectively. The analysis of spectropolarimetric data obtained by the Interferometric Bidimensional Spectrometer over the brightening regions suggests untwisting of field lines, which further supports TCR. Filaments near polarity inversion line region, resulted from TCR of low lying sheared loops, undergo merging and form an elongated filament. The temperature and density differences between footpoints of the merged filament, revealed by DEM analysis, caused streaming and counter-streaming of plasma flow along the filament and unloads at its footpoints with an average velocity of $\approx$ 40 km s$^{-1}$. This results in decrease of mass of the filament (density decreased by $>50\%$), leading to its rise and expansion outwards. However, due to strong strapping flux, the filament separates itself instead of erupting. Further, the evolution of non-potential parameters describes the characteristics of confinedness of the flare. Our study suggests that the sigmoid-filament system exhibits upward catastrophe due to mass unloading, but gets suppressed by strong confinement of external poloidal field.

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N. Vasantharaju, F. Zuccarello, F. Ferrente, et. al.
Tue, 25 Apr 23
13/72

Comments: Manuscript has 20 pages, 10 figures and accepted for Publication in the ApJ on 23 April 2023

Transition disc nature of post-AGB binary systems confirmed by mid-infrared interferometry [SSA]

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http://arxiv.org/abs/2304.12028


Circumbinary discs around evolved post-asymptotic giant branch (post-AGB) binary systems show many similar properties to protoplanetary discs around young stars. Deficits of near-infrared (near-IR) flux in the spectral energy distributions (SEDs) of such systems hints towards large dust-free cavities, reminiscent of transition discs as commonly observed around young stars. We aim to assess the inner rim size of 6 post-AGB binary systems with such a lack in near-IR using resolved mid-IR high-angular resolution observations of VLTI/MATISSE and VLTI/MIDI. The inner rim of only one such system was previously resolved. We compare these inner rim sizes to 5 systems with available MATISSE data that were identified to host a disc starting at the dust sublimation radius. We used geometric ring models to estimate the inner rim sizes, the relative flux contributions of the star, the ring, and an over-resolved emission, the orientation of the ring, and the spectral dependencies of the components. We find that the dust inner rims of the targets with a lack of near-IR excess in their SEDs are 2.5 to 7.5 times larger than the theoretical dust sublimation radii while the systems that do not show such a deficit have inner rim sizes similar to their dust sublimation radii. Physical radii of the inner rims of these transition discs around post-AGB binaries are 3-25 au, which are larger than the disc sizes inferred for transition discs around young stars with VLTI/MIDI. This is due to the higher stellar luminosities of post-AGB systems compared to young stars, implying larger dust sublimation radii and thus larger physical transition disc inner radii. With mid-IR interferometric data we directly confirm the transition disc nature of six discs around post-AGB binary systems. Future observational and modelling efforts are needed to progress on the structure, origin, and evolution of these transition discs.

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A. Corporaal, J. Kluska, H. Winckel, et. al.
Tue, 25 Apr 23
18/72

Comments: accepted for publication in A&A. 13 pages, including appendices

Thermodynamic properties of small flares in the quiet Sun observed by H$α$ and EUV: plasma motion of the chromosphere and time evolution of temperature/emission measure [SSA]

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http://arxiv.org/abs/2304.12037


Small flares frequently occur in the quiet Sun. Previous studies have noted that they share many common characteristics with typical solar flares in active regions. However, their similarities and differences are not fully understood, especially their thermal properties. In this study, we performed imaging spectroscopic observations in the H$\alpha$ line taken with the Solar Dynamics Doppler Imager on the Solar Magnetic Activity Research Telescope (SMART/SDDI) at the Hida Observatory and imaging observations with the Atmospheric Imaging Assembly onboard Solar Dynamics Observatory (SDO/AIA). We analysed 25 cases of small flares in the quiet Sun over the thermal energy range of $10^{24}-10^{27}\,\mathrm{erg}$, paying particular attention to their thermal properties. Our main results are as follows: (1) We observe a redshift together with line centre brightening in the H$\alpha$ line associated with more than half of the small flares. (2) We employ differential emission measure analysis using AIA multi-temperature (channel) observations to obtain the emission measure and temperature of the small flares. The results are consistent with the Shibata & Yokoyama (1999, 2002) scaling law. From the scaling law, we estimated the coronal magnetic field strength of small flares to be 5 –15 G. (3) The temporal evolution of the temperature and the density shows that the temperature peaks precede the density peaks in more than half of the events. These results suggest that chromospheric evaporations/condensations play an essential role in the thermal properties of some of the small flares in the quiet Sun, as does for large flares.

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Y. Kotani, T. Ishii, D. Yamasaki, et. al.
Tue, 25 Apr 23
21/72

Comments: 14 pages, 12 figures, accepted for publication in MNRAS

The properties of small magnetic flux ropes inside the solar wind come from coronal holes, active regions, and quiet Sun [SSA]

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http://arxiv.org/abs/2304.11802


The origination and generation mechanisms of small magnetic flux ropes (SFRs), which are important structures in solar wind, are not clearly known. In present study, 1993 SFRs immersed in coronal holes, active regions, and quiet Sun solar wind are analyzed and compared. We find that the properties of SFRs immersed in three types of solar wind are signicantly different. The SFRs are further classifed into hot-SFRs, cold-SFRs, and normal-SFRs, according to whether the O7+/O6+ is 30% elevated or dropped inside SFRs as compared with background solar wind. Our studies show that the parameters of normal-SFRs are similar to background in all three types of solar wind. The properties of hot-SFRs and cold-SFRs seem to be lying in two extremes. Statistically, the hot-SFRs (cold-SFRs) are associated with longer (shorter) duration, lower (higher) speeds and proton temperatures, higher (lower) charge states, helium abundance, and FIP bias as compared with normal-SFRs and background solar wind. The anti-correlations between speed and O7+/O6+ inside hot-SFRs (normal-SFRs) are different from (similar to) those in background solar wind. Most of hot-SFRs and cold-SFRs should come from the Sun. Hot-SFRs may come from streamers associated with plasma blobs and/or small-scale activities on the Sun. Cold-SFRs may be accompanied by small-scale eruptions with lower-temperature materials. Both hot-SFRs and cold-SFRs could also be formed by magnetic erosions of ICMEs that do not contain or contain cold-filament materials. The characteristics of normal-SFRs can be explained reasonably by the two originations, from the Sun and generated in the heliosphere both.

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C. Zhai, H. Fu, J. Si, et. al.
Tue, 25 Apr 23
39/72

Comments: 19 pages, 5 figures

Statistical Investigation of the Widths of Supra-arcade Downflows Observed During a Solar Flare [SSA]

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http://arxiv.org/abs/2304.11307


Supra-arcade downflows (SADs) are dark voids descending towards the post-reconnection flare loops and exhibit obvious variation in properties like width. However, due to the lack of further statistical studies, the mechanism behind such variations hitherto remains elusive. Here we statistically investigated widths of 81 SADs observed in one flare by the Solar Dynamics Observatory (SDO). For each of SADs, six moments were selected with equal time intervals to measure their widths at different stages of their evolution. It is found that most SADs show a roughly monotonous width decrease during their descents, while some SADs with small initial widths can have complex evolutions. 3D reconstruction results based on SDO and Solar Terrestrial Relations Observatory Ahead (STEREO-A) images and thermal properties analysis reveal that differences in magnetic and plasma environments may result in that SADs in the north are overall wider than those in the south. Additionally, correlation analysis between the width and other parameters of SADs was further conducted and revealed that: (1) SADs with different initial widths show no significant differences in their temperature and density evolution characteristics; (2) SADs with small initial widths usually appear in lower heights, where more frequent collisions between SADs could lead to their intermittent acceleration, width increment, and curved trajectories. These results indicate that SADs with different initial widths are produced the same way while different environments (magnetic field or plasma) could affect their subsequent width evolutions.

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G. Tan, Y. Hou and H. Tian
Tue, 25 Apr 23
44/72

Comments: 15 pages, 12 figures, 1 table. Accepted for publication in MNRAS

The Gaia-ESO Survey: Empirical estimates of stellar ages from lithium equivalent widths (EAGLES) [SSA]

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http://arxiv.org/abs/2304.12197


We present an empirical model of age-dependent photospheric lithium depletion, calibrated using a large, homogeneously-analysed sample of 6200 stars in 52 open clusters, with ages from 2–6000 Myr and $-0.3<{\rm [Fe/H}]<0.2$, observed in the Gaia-ESO spectroscopic survey. The model is used to obtain age estimates and posterior age probability distributions from measurements of the Li I 6708A equivalent width for individual (pre) main sequence stars with $3000 < T_{\rm eff}/{\rm K} <6500$, a domain where age determination from the HR diagram is either insensitive or highly model-dependent. In the best cases, precisions of 0.1 dex in log age are achievable; even higher precision can be obtained for coeval groups and associations where the individual age probabilities of their members can be combined. The method is validated on a sample of exoplanet-hosting young stars, finding agreement with claimed young ages for some, but not others. We obtain better than 10 per cent precision in age, and excellent agreement with published ages, for seven well-studied young moving groups. The derived ages for young clusters ($<1$ Gyr) in our sample are also in good agreement with their training ages, and consistent with several published, model-insensitive lithium depletion boundary ages. For older clusters there remain systematic age errors that could be as large as a factor of two. There is no evidence to link these errors to any strong systematic metallicity dependence of (pre) main sequence lithium depletion, at least in the range $-0.29 < {\rm [Fe/H]} < 0.18$. Our methods and model are provided as software — “Empirical AGes from Lithium Equivalent widthS” (EAGLES).

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R. Jeffries, R. Jackson, N. Wright, et. al.
Tue, 25 Apr 23
55/72

Comments: Accepted for publication in Monthly Notices of the Royal Astronomical Society

The APO-K2 Catalog. I. 7,673 Red Giants with Fundamental Stellar Parameters from APOGEE DR17 Spectroscopy and K2-GAP Asteroseismology [SSA]

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http://arxiv.org/abs/2304.10654


We present a catalog of fundamental stellar properties for 7,673 evolved stars, including stellar radii and masses, determined from the combination of spectroscopic observations from the Apache Point Observatory Galactic Evolution Experiment (APOGEE), part of the Sloan Digital Sky Survey IV (SDSS), and asteroseismology from K2. The resulting APO-K2 catalog provides spectroscopically derived temperatures and metallicities, asteroseismic global parameters, evolutionary states, and asteroseismically-derived masses and radii. Additionally, we include kinematic information from \textit{Gaia}. We investigate the multi-dimensional space of abundance, stellar mass, and velocity with an eye toward applications in Galactic archaeology. The APO-K2 sample has a large population of low metallicity stars ($\sim$288 at [M/H] $\leq$ $-$1), and their asteroseismic masses are larger than astrophysical estimates. We argue that this may reflect offsets in the adopted fundamental temperature scale for metal-poor stars rather than metallicity-dependent issues with interpreting asteroseismic data. We characterize the kinematic properties of the population as a function of $\alpha$-enhancement and position in the disk and identify those stars in the sample that are candidate components of the \textit{Gaia-Enceladus} merger. Importantly, we characterize the selection function for the APO-K2 sample as a function of metallicity, radius, mass, $\nu_{\mathrm{max}}$, color, and magnitude referencing Galactic simulations and target selection criteria to enable robust statistical inferences with the catalog.

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J. Schonhut-Stasik, J. Zinn, K. Stassun, et. al.
Mon, 24 Apr 23
5/41

Comments: 28 Pages, 14 Figures, 1 Table. Full table and selection function data available at this https URL Submitted April 18th 2023 with AJ, awaiting review

VLBI Astrometry of Radio Stars to Link Radio and Optical Celestial Reference Frames. I. HD 199178 $\&$ AR Lacertae [SSA]

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http://arxiv.org/abs/2304.10886


To accurately link the radio and optical Celestial Reference Frames (CRFs) at optical bright end, i.e., with Gaia G band magnitude < 13, increasing number and improving sky distribution of radio stars with accurate astrometric parameters from both Very Long Baseline Interferometry (VLBI) and Gaia measurements are mandatory. We selected two radio stars HD 199178 and AR Lacertae as the target for a pilot program for the frame link, using the Very Long Baseline Array (VLBA) at 15 GHz at six epochs spanning about 1 year, to measure their astrometric parameters. The measured parallax of HD 199178 is $8.949 \pm 0.059$ mas and the proper motion is $\mu_\alpha cos \delta = 26.393 \pm 0.093$, $\mu_\delta = -0.950 \pm 0.083~mas~yr^{-1}$, while the parallax of AR Lac is $23.459 \pm 0.094$ mas and the proper motion is $\mu_\alpha cos \delta = -51.906 \pm 0.138$, $\mu_\delta = 46.732 \pm 0.131~mas~yr^{-1}$. Our VLBI measured astrometric parameters have accuracies about 4-5 times better than the corresponding historic VLBI measurements and comparable accuracies with those from Gaia, validating the feasibility of frame link using radio stars. With the updated astrometric parameters for these two stars, there is a 25% reduction of the uncertainties on the Y axis for both orientation and spin parameters.

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W. Chen, B. Zhang, J. Zhang, et. al.
Mon, 24 Apr 23
17/41

Comments: 11 pages, accepted by MNRAS on 2023 April 20

Optical color of Type Ib and Ic supernovae and implications for their progenitors [SSA]

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http://arxiv.org/abs/2304.10670


Type Ib and Ic supernovae (SNe Ib/Ic) originate from hydrogen-deficient massive star progenitors, of which the exact properties are still much debated. Using the SN data in the literature, we investigate the optical $B-V$ color of SNe Ib/Ic at the $V-$band peak and show that SNe Ib are systematically bluer than SNe Ic. We construct SN models from helium-rich and helium-poor progenitors of various masses using the radiation hydrodynamics code STELLA and discuss how the $B-V$ color at the $V-$band peak is affected by $^{56}$Ni to ejecta mass ratios, $^{56}$Ni mixing and presence/absence of the helium envelope. We argue that the dichotomy in the amounts of helium in the progenitors plays the primary role in making the observed systematic color difference at the optical peak, in favor of the most commonly invoked SN scenario that SNe Ib and SNe Ic progenitors are helium-rich and helium-poor, respectively.

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H. Jin, S. Yoon and S. Blinnikov
Mon, 24 Apr 23
24/41

Comments: Accepted for publication in ApJ. 16 pages

The Evolution of Population III and Extremely Metal-Poor Binary Stars [SSA]

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http://arxiv.org/abs/2304.11078


Numerical simulations have now shown that Population III (Pop III) stars can form in binaries and small clusters and that these stars can be in close proximity to each other. If so, they could be subject to binary interactions such as mass exchange that could profoundly alter their evolution, ionizing UV and Lyman-Werner (LW) photon emission and explosion yields, with important consequences for early cosmological reionization and chemical enrichment. Here we investigate the evolution of Pop III and extremely metal-poor binary stars with the MESA code. We find that interactions ranging from stable mass transfer to common envelope evolution can occur in these binaries for a wide range of mass ratios and initial separations. Mass transfer can nearly double UV photon yields in some of these binaries with respect to their individual stars by extending the life of the companion star, which in turn can enhance early cosmological reionization but also suppress the formation of later generations of primordial stars. Binary interactions can also have large effects on the nucleosynthetic yields of the stars by promoting or removing them into or out of mass ranges for specific SN types. We provide fits to total photon yields for the binaries in our study for use in cosmological simulations.

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S. Tsai, K. Chen, D. Whalen, et. al.
Mon, 24 Apr 23
40/41

Comments: N/A

WD J004917.14$-$252556.81, the Most Massive Pulsating White Dwarf [SSA]

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http://arxiv.org/abs/2304.10330


We present APO and Gemini time-series photometry of WD J004917.14$-$252556.81, an ultramassive DA white dwarf with $T_{\rm eff} = 13020$ K and $\log{g} = 9.34$. We detect variability at two significant frequencies, making J0049$-$2525 the most massive pulsating white dwarf currently known with $M_\star=1.31~M_{\odot}$ (for a CO core) or $1.26~M_{\odot}$ (for an ONe core). J0049$-$2525 does not display any of the signatures of binary mergers, there is no evidence of magnetism, large tangential velocity, or rapid rotation. Hence, it likely formed through single star evolution and is likely to have an ONe core. Evolutionary models indicate that its interior is $\gtrsim99$% crystallized. Asteroseismology offers an unprecedented opportunity to probe its interior structure. However, the relatively few pulsation modes detected limit our ability to obtain robust seismic solutions. Instead, we provide several representative solutions that could explain the observed properties of this star. Extensive follow-up time-series photometry of this unique target has the potential to discover a significant number of additional pulsation modes that would help overcome the degeneracies in the asteroseismic fits, and enable us to probe the interior of an $\approx1.3~M_{\odot}$ crystallized white dwarf.

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M. Kilic, A. Córsico, A. Moss, et. al.
Fri, 21 Apr 23
7/60

Comments: MNRAS, in press

Constraints on Magnetic Braking from the G8 Dwarf Stars 61 UMa and $τ$ Cet [SSA]

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http://arxiv.org/abs/2304.09896


During the first half of their main-sequence lifetimes, stars rapidly lose angular momentum to their magnetized winds, a process known as magnetic braking. Recent observations suggest a substantial decrease in the magnetic braking efficiency when stars reach a critical value of the Rossby number, the stellar rotation period normalized by the convective overturn timescale. Cooler stars have deeper convection zones with longer overturn times, reaching this critical Rossby number at slower rotation rates. The nature and timing of the transition to weakened magnetic braking has previously been constrained by several solar analogs and two slightly hotter stars. In this Letter, we derive the first direct constraints from stars cooler than the Sun. We present new spectropolarimetry of the old G8 dwarf $\tau$ Cet from the Large Binocular Telescope, and we reanalyze a published Zeeman Doppler image of the younger G8 star 61 UMa, yielding the large-scale magnetic field strengths and morphologies. We estimate mass-loss rates using archival X-ray observations and inferences from Ly$\alpha$ measurements, and we adopt other stellar properties from asteroseismology and spectral energy distribution fitting. The resulting calculations of the wind braking torque demonstrate that the rate of angular momentum loss drops by a factor of 300 between the ages of these two stars (1.4-9 Gyr), well above theoretical expectations. We summarize the available data to help constrain the value of the critical Rossby number, and we identify a new signature of the long-period detection edge in recent measurements from the Kepler mission.

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T. Metcalfe, K. Strassmeier, I. Ilyin, et. al.
Fri, 21 Apr 23
15/60

Comments: ApJ Letters (accepted), 6 pages including 3 figures and 1 table. Python code is available at this https URL

A large bubble around the AGB star R Dor detected in the UV [SSA]

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http://arxiv.org/abs/2304.10173


Many asymptotic giant branch (AGB) and supergiant stars exhibit extended detached shells in the far-infrared, resembling rings or arcs. These structures have long been interpreted as the bow shock formed in the interface between the stellar wind and the interstellar medium, the astrosphere. To date, only a few AGB stars have been observed showing an extended shell in the ultraviolet: the cometary tail drifting away from $o$ Ceti, and a bubble around IRC+10216, CIT6, and U Hya. This paper describes a search of UV extended shells around AGB stars using archival GALEX far-UV images. After inspecting visually 282 GALEX images, we identified the fourth discovery of a UV bubble around the AGB star R Dor. The bubble is seen as a 26’x29′ ring, corresponding to an actual diameter of 0.41×0.46 parsec$^2$. The mass of the thin UV bubble is estimated to be $\simeq$0.003 $M_{\odot}$. The morphological asymmetry (less than $\sim 20$\%) and brightness variations of this shell are uncorrelated with the stellar proper motion and thus they can rather be ascribed to inhomogeneities in the ISM. Archival \emph{IRAS} 60 and 100$\mu$m images reveal that the bubble is filled with cold (i.e. < 32 K) dust. All UV bubbles known to date are limited to be within a distance < 350 pc and at high Galactic latitudes (|b| > 35 degree), which suggests that their detection is hampered in most cases by the strong UV interstellar extinction.

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R. Ortiz and M. Guerrero
Fri, 21 Apr 23
22/60

Comments: 8 pages, 5 figures, to be published in MNRAS

NGTS clusters survey IV. Search for Dipper stars in the Orion Nebular Cluster [SSA]

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http://arxiv.org/abs/2304.09942


The dipper is a novel class of young stellar object associated with large drops in flux on the order of 10 to 50 per cent lasting for hours to days. Too significant to arise from intrinsic stellar variability, these flux drops are currently attributed to disk warps, accretion streams, and/or transiting circumstellar dust. Dippers have been previously studied in young star forming regions including the Orion Complex. Using Next Generation Transit Survey (NGTS) data, we identified variable stars from their lightcurves. We then applied a machine learning random forest classifier for the identification of new dipper stars in Orion using previous variable classifications as a training set. We discover 120 new dippers, of which 83 are known members of the Complex. We also investigated the occurrence rate of disks in our targets, again using a machine learning approach. We find that all dippers have disks, and most of these are full disks. We use dipper periodicity and model-derived stellar masses to identify the orbital distance to the inner disk edge for dipper objects, confirming that dipper stars exhibit strongly extended sublimation radii, adding weight to arguments that the inner disk edge is further out than predicted by simple models. Finally, we determine a dipper fraction (the fraction of stars with disks which are dippers) for known members of 27.8 plus minus 2.9 per cent. Our findings represent the largest population of dippers identified in a single cluster to date.

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T. Moulton, S. Hodgkin, G. Smith, et. al.
Fri, 21 Apr 23
30/60

Comments: 28 pages, 34 figures

3D hydrodynamic simulations of massive main-sequence stars. III. The effect of radiation pressure and diffusion leading to a 1D equilibrium model [SSA]

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http://arxiv.org/abs/2304.10470


We present 3D hydrodynamical simulations of core convection with a stably stratified envelope of a 25 $\mathrm{M}_\odot$ star in the early phase of the main-sequence. We use the explicit gas-dynamics code $\texttt{PPMstar}$ which tracks two fluids and includes radiation pressure and radiative diffusion. Multiple series of simulations with different luminosities and radiative thermal conductivities are presented. The entrainment rate at the convective boundary, internal gravity waves in and above the boundary region, and the approach to dynamical equilibrium shortly after a few convective turnovers are investigated. From the results of these simulations we extrapolate to find the entrainment rate at the nominal heating rate and thermal diffusion given by the $\texttt{MESA}$ stellar evolution model on which the 3D stratification is based. Further, to study the effect of radiative diffusion on the thermal timescale, we perform very long simulations accelerated by 10000 times their nominal luminosities. In these simulations the growing penetrative convection reduces the initially unrealistically large entrainment. This reduction is enabled by a spatial separation that develops between the entropy gradient and the composition gradient. The convective boundary moves outward much more slowly at the end of these simulations. Finally, we present a method to predict the extent and character of penetrative convection beyond the Schwarzschild boundary. This method is intended to be ultimately deployed in 1D stellar evolution calculations and is based on the properties of penetrative convection in our simulations carried forward through the local thermal timescale.

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H. Mao, P. Woodward, F. Herwig, et. al.
Fri, 21 Apr 23
48/60

Comments: 33 pages, 31 figures; submitted to ApJ

Accurate mass-radius ratios for Hyades white dwarfs [SSA]

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http://arxiv.org/abs/2304.10485


We use the ESPRESSO spectrograph at the Very Large Telescope to measure velocity shifts and gravitational redshifts of eight bona fide Hyades white dwarfs, with an accuracy better than 1.5 percent. By comparing the gravitational redshift measurements of the mass-to-radius ratio with the same ratios derived by fitting the \textit{Gaia} photometry with theoretical models, we find an agreement to better than one per cent. It is possible to reproduce the observed white dwarf cooling sequence and the trend of the mass-to-radius ratios as a function of colour using isochrones with ages between 725 and 800 Myr, tuned for the Hyades. One star, EGGR\,29, consistently stands out in all diagrams, indicating that it is possibly the remnant of a blue straggler. We also computed mass-to-radius ratios from published gravities and masses, determined from spectroscopy. The comparison between photometric and spectroscopic stellar parameters reveals that spectroscopic effective temperature and gravity are systematically larger than the photometric values. Spectroscopic mass-to-radius ratios disagree with those measured from gravitational redshift, indicating the presence of systematics affecting the white dwarf parameters derived from the spectroscopic analysis.

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L. Pasquini, A. Pala, M. Salaris, et. al.
Fri, 21 Apr 23
58/60

Comments: MNRAS, accepted for pubblication

ASASSN-18aan revisited [SSA]

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http://arxiv.org/abs/2304.09829


The light curve of the cataclismic variable ASASSN-18aan is studied using recent observations of the MC589 Observatory, giving an orbital Period and Epoch fully consistent with the data obtained after the discovery flare in 2018. Archival data from ASASSN, ZTF and Gaia were used to check if its flares have a quasi-periodic behaviour. A recurrency time scale of about 11 months is found, confirming a previous tentative result using the historic plate archive of the Asiago Observatory. The next outbursts are expected by April 2023 and March 2024.

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R. Nesci, A. Vagnozzi and S. Valentini
Thu, 20 Apr 23
3/57

Comments: 7 pages, 2 figures, published on OEJV

The magnetic field and multiple planets of the young dwarf AU~Mic [SSA]

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http://arxiv.org/abs/2304.09642


In this paper we present an analysis of near-infrared spectropolarimetric and velocimetric data of the young M dwarf AU Mic, collected with SPIRou at the Canada-France-Hawaii telescope from 2019 to 2022, mostly within the SPIRou Legacy Survey. With these data, we study the large- and small-scale magnetic field of AU Mic, detected through the unpolarized and circularly-polarized Zeeman signatures of spectral lines. We find that both are modulated with the stellar rotation period (4.86 d), and evolve on a timescale of months under differential rotation and intrinsic variability. The small-scale field, estimated from the broadening of spectral lines, reaches $2.61\pm0.05$ kG. The large-scale field, inferred with Zeeman-Doppler imaging from Least-Squares Deconvolved profiles of circularly-polarized and unpolarized spectral lines, is mostly poloidal and axisymmetric, with an average intensity of $550\pm30$ G. We also find that surface differential rotation, as derived from the large-scale field, is $\simeq$30% weaker than that of the Sun. We detect the radial velocity (RV) signatures of transiting planets b and c, although dwarfed by activity, and put an upper limit on that of candidate planet d, putatively causing the transit-timing variations of b and c. We also report the detection of the RV signature of a new candidate planet (e) orbiting further out with a period of $33.39\pm0.10$ d, i.e., near the 4:1 resonance with b. The RV signature of e is detected at 6.5$\sigma$ while those of b and c show up at $\simeq$4$\sigma$, yielding masses of $10.2^{+3.9}{-2.7}$ and $14.2^{+4.8}{-3.5}$ Earth masses for b and c, and a minimum mass of $35.2^{+6.7}_{-5.4}$ Earth masses for e.

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D. JF, C. PI, F. B, et. al.
Thu, 20 Apr 23
5/57

Comments: MNRAS, in press (20 pages and 12 figures + 9 pages of supplementary material)

The SunPy Project: An Interoperable Ecosystem for Solar Data Analysis [SSA]

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http://arxiv.org/abs/2304.09794


The SunPy Project is a community of scientists and software developers creating an ecosystem of Python packages for solar physics. The project includes the sunpy core package as well as a set of affiliated packages. The sunpy core package provides general purpose tools to access data from different providers, read image and time series data, and transform between commonly used coordinate systems. Affiliated packages perform more specialized tasks that do not fall within the more general scope of the sunpy core package. In this article, we give a high-level overview of the SunPy Project, how it is broader than the sunpy core package, and how the project curates and fosters the affiliated package system. We demonstrate how components of the SunPy ecosystem, including sunpy and several affiliated packages, work together to enable multi-instrument data analysis workflows. We also describe members of the SunPy Project and how the project interacts with the wider solar physics and scientific Python communities. Finally, we discuss the future direction and priorities of the SunPy Project.

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S. Community, W. Barnes, S. Christe, et. al.
Thu, 20 Apr 23
22/57

Comments: 15 pages, 1 figure, published in Frontiers

3D simulations of AGB stellar winds — II. Ray-tracer implementation and impact of radiation on the outflow morphology [SSA]

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http://arxiv.org/abs/2304.09786


Stars with an initial mass below ~ 8 Msun evolve through the asymptotic giant branch (AGB) phase, during which they develop strong stellar winds. Recent observations have revealed significant morphological complexities in their outflows, most likely caused by a companion. We study the impact of the radiation force on such companion-perturbed AGB outflows. We present the implementation of a ray tracer for radiative transfer in smoothed particle hydrodynamics (SPH) and compared four different descriptions of radiative transfer: the free-wind, the geometrical, the Lucy, and the attenuation approximation. For both low and high mass-loss rates, the velocity profile of the outflow is modified when going from the free-wind to the geometrical approximation, also resulting in a different morphology. In the case of a low mass-loss rate, the effect of the Lucy and attenuation approximation is negligible due to the low densities but morphological differences appear in the high mass-loss rate regime. By comparing the radiative equilibrium temperature and radiation force to full 3D radiative transfer, we show that the Lucy approximation works best. Although, close to the companion, artificial heating occurs and it fails to simulate the shadow cast by the companion. The attenuation approximation produces a lower equilibrium temperature and weaker radiation force, but it produces the shadow cast by the companion. From the predictions of the 3D radiative transfer, we also conclude that a radially directed radiation force is a reasonable assumption. The radiation force thus plays a critical role in dust-driven AGB winds, impacting the velocity profile and morphological structures. For low mass-loss rates, the geometrical approximation suffices, while high mass-loss rates require a more rigorous method, where the Lucy approximation provides the most accurate results although not accounting for all effects.

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M. Esseldeurs, L. Siess, F. Ceuster, et. al.
Thu, 20 Apr 23
35/57

Comments: N/A

Slow Solar Wind Connection Science during Solar Orbiter's First Close Perihelion Passage [SSA]

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http://arxiv.org/abs/2304.09570


The Slow Solar Wind Connection Solar Orbiter Observing Plan (Slow Wind SOOP) was developed to utilise the extensive suite of remote sensing and in situ instruments on board the ESA/NASA Solar Orbiter mission to answer significant outstanding questions regarding the origin and formation of the slow solar wind. The Slow Wind SOOP was designed to link remote sensing and in situ measurements of slow wind originating at open-closed field boundaries. The SOOP ran just prior to Solar Orbiter’s first close perihelion passage during two remote sensing windows (RSW1 and RSW2) between 2022 March 3-6 and 2022 March 17-22, while Solar Orbiter was at a heliocentric distance of 0.55-0.51 and 0.38-0.34 au from the Sun, respectively. Coordinated observation campaigns were also conducted by Hinode and IRIS. The magnetic connectivity tool was used, along with low latency in situ data, and full-disk remote sensing observations, to guide the target pointing of Solar Orbiter. Solar Orbiter targeted an active region complex during RSW1, the boundary of a coronal hole, and the periphery of a decayed active region during RSW2. Post-observation analysis using the magnetic connectivity tool along with in situ measurements from MAG and SWA/PAS, show that slow solar wind, with velocities between 210 and 600 km/s, arrived at the spacecraft originating from two out of the three of the target regions. The Slow Wind SOOP, despite presenting many challenges, was very successful, providing a blueprint for planning future observation campaigns that rely on the magnetic connectivity of Solar Orbiter.

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S. Yardley, C. Owen, D. Long, et. al.
Thu, 20 Apr 23
47/57

Comments: 24 pages, 10 figures