Application of the disk instability model to all Quasi-Periodic Eruptions [HEAP]

http://arxiv.org/abs/2305.02071


After the first quasi-periodic eruptions (QPEs, GSN069) was reported in 2019, four other sources have been identified as QPEs or its candidate. However, the physics behind QPEs is still unclear so far, though several models have been proposed. Pan et al. (2022) proposed an instability model for the accretion disk with magnetically driven outflows in the first QPEs GSN 069, which is able to reproduce both the light curve and the evolution of spectrum fairly well. In this work, we exploit this model to all the QPEs. We imporve the calculations of the spectrum of disk by introducing a hardening factor, which is caused by the deviation of opacity from the blackbody. We find that the light curves and evolution of the spectra of the four QPEs or candidate can all be well reproduced by our model calculations.

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X. Pan, S. Li and X. Cao
Thu, 4 May 23
5/60

Comments: 8 pages, 7 figures, accepted for publication in ApJ

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

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]

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]

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]

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]

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]

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]

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]

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]

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

Photosynthesis Under a Red Sun: Predicting the absorption characteristics of an extraterrestrial light-harvesting antenna [EPA]

http://arxiv.org/abs/2305.02067


Here we discuss the feasibility of photosynthesis on Earth-like rocky planets in close orbit around ultra-cool red dwarf stars. Stars of this type have very limited emission in the \textit{photosynthetically active} region of the spectrum ($400 – 700$ nm), suggesting that they may not be able to support oxygenic photosynthesis. However, photoautotrophs on Earth frequently exploit very dim environments with the aid of highly structured and extremely efficient antenna systems. Moreover, the anoxygenic photosynthetic bacteria, which do not need to oxidize water to source electrons, can exploit far red and near infrared light. Here we apply a simple model of a photosynthetic antenna to a range of model stellar spectra, ranging from ultra-cool (2300 K) to Sun-like (5800 K). We assume that a photosynthetic organism will evolve an antenna that maximizes the rate of energy input while also minimizing fluctuations. The latter is the ‘noise cancelling’ principle recently reported by Arp et al. 2020. Applied to the Solar spectrum this predicts optimal antenna configurations in agreement with the chlorophyll Soret absorption bands. Applied to cooler stars, the optimal antenna peaks become redder with decreasing stellar temperature, crossing to the typical wavelength ranges associated with anoxygenic photoautotrophs at $\sim 3300$ K. Lastly, we compare the relative input power delivered by antennae of equivalent size around different stars and find that the predicted variation is within the same order of magnitude. We conclude that low-mass stars do not automatically present light-limiting conditions for photosynthesis but they may select for anoxygenic organisms.

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C. Duffy, G. Canchon, T. Haworth, et. al.
Thu, 4 May 23
47/60

Comments: Resubmitted to MNRAS

Wapiti: a data-driven approach to correct for systematics in RV data — Application to SPIRou data of the planet-hosting M dwarf GJ 251 [EPA]

http://arxiv.org/abs/2305.02123


Context: Recent advances in the development of precise radial velocity (RV) instruments in the near-infrared (nIR) domain, such as SPIRou, have facilitated the study of M-type stars to more effectively characterize planetary systems. However, the nIR presents unique challenges in exoplanet detection due to various sources of planet-independent signals which can result in systematic errors in the RV data.
Aims: In order to address the challenges posed by the detection of exoplanetary systems around M-type stars using nIR observations, we introduce a new data-driven approach for correcting systematic errors in RV data. The effectiveness of this method is demonstrated through its application to the star GJ\,251.
Methods: Our proposed method, referred to as \texttt{Wapiti} (Weighted principAl comPonent analysIs reconsTructIon), uses a dataset of per-line RV time-series generated by the line-by-line (LBL) algorithm and employs a weighted principal component analysis (wPCA) to reconstruct the original RV time-series. A multi-step process is employed to determine the appropriate number of components, with the ultimate goal of subtracting the wPCA reconstruction of the per-line RV time-series from the original data in order to correct systematic errors.
Results: The application of \texttt{Wapiti} to GJ\,251 successfully eliminates spurious signals from the RV time-series and enables the first detection in the nIR of GJ\,251b, a known temperate super-Earth with an orbital period of 14.2 days. This demonstrates that, even when systematics in SPIRou data are unidentified, it is still possible to effectively address them and fully realize the instrument’s capability for exoplanet detection. Additionally, in contrast to the use of optical RVs, this detection did not require to filter out stellar activity, highlighting a key advantage of nIR RV measurements.

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M. Ould-Elhkim, C. Moutou, J. Donati, et. al.
Thu, 4 May 23
48/60

Comments: Submitted to A&A. For the publicly available Wapiti code, see this https URL

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

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

Production of n-rich nuclei in red giant stars [CL]

http://arxiv.org/abs/2305.01549


We outline a partial historical summary of the steps through which the nucleosynthesis phenomena induced by {\it slow} neutron captures (the {\it s-process}) were clarified, a scientific achievement in which Franz K\”appeler played a major role. We start by recalling the early phenomenological approach, which yielded a basic understanding of the subject even before models for the parent stellar evolutionary stages were developed. Through such a tool, rough limits for the neutron density and exposure were set, and the crucial fact was understood that more than one nucleosynthesis component is required to account for solar abundances of $s$-process nuclei up to the Pb-Bi region. We then summarize the gradual understanding of the stellar processes actually involved in the production of nuclei from Sr to Pb (the so-called {\it Main Component}, achieved in the last decade of the past century and occurring in red giants of low and intermediate mass, ($M \lesssim$ 8 $M_{\odot}$), populating, in the {\it HR} diagram, the {\it Asymptotic Giant Branch} or {\it AGB} region. We conclude by giving some details on more recent research concerning mixing mechanisms inducing the activation of the main neutron source, $^{13}$C($\alpha$,n)$^{16}$O.

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M. Busso and S. Palmerini
Wed, 3 May 23
3/67

Comments: 35 page, 8 figures

Structural Analysis of Open Cluster Bochum 2 [SSA]

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

Joint Modeling of Radial Velocities and Photometry with a Gaussian Process Framework [EPA]

http://arxiv.org/abs/2305.00988


Developments in the stability of modern spectrographs have led to extremely precise instrumental radial velocity (RV) measurements. For most stars, the detection limit of planetary companions with these instruments is expected to be dominated by astrophysical noise sources such as starspots. Correlated signals caused by rotationally-modulated starspots can obscure or mimic the Doppler shifts induced by even the closest, most massive planets. This is especially true for young, magnetically active stars where stellar activity can cause fluctuation amplitudes of $\gtrsim$0.1 mag in brightness and $\gtrsim$100 m s$^{-1}$ in RV semi-amplitudes. Techniques that can mitigate these effects and increase our sensitivity to young planets are critical to improving our understanding of the evolution of planetary systems. Gaussian processes (GPs) have been successfully employed to model and constrain activity signals in individual cases. However, a principled approach of this technique, specifically for the joint modeling of photometry and RVs, has not yet been developed. In this work, we present a GP framework to simultaneously model stellar activity signals in photometry and RVs that can be used to investigate the relationship between both time series. Our method, inspired by the $\textit{FF}^\prime$ framework of (Aigrain et al. 2012), models spot-driven activity signals as the linear combinations of two independent latent GPs and their time derivatives. We also simulate time series affected by starspots by extending the $\texttt{starry}$ software (Luger et al. 2019) to incorporate time evolution of stellar features. Using these synthetic datasets, we show that our method can predict spot-driven RV variations with greater accuracy than other GP approaches.

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Q. Tran, M. Bedell, D. Foreman-Mackey, et. al.
Wed, 3 May 23
12/67

Comments: 19 pages, 10 figures

Gravitational Redshift Detection from the Magnetic White Dwarf Harbored in RX J1712.6-2414 [HEAP]

http://arxiv.org/abs/2305.01496


Gravitational redshift is a fundamental parameter that allows us to determine the mass-to-radius ratio of compact stellar objects, such as black holes, neutron stars, and white dwarfs (WDs). In the X-ray spectra of the close binary system, RX J1712.6$-$2414, obtained from the Chandra High-Energy Transmission Grating observation, we detected significant redshifts for characteristic X-rays emitted from hydrogen-like magnesium, silicon ($\Delta E/E_{\rm rest} \sim 7 \times 10^{-4}$), and sulfur ($\Delta E/E_{\rm rest} \sim 15 \times 10^{-4}$) ions, which are over the instrumental absolute energy accuracy (${\Delta E/E_{\rm rest} \sim 3.3} \times 10^{-4}$). Considering some possible factors, such as Doppler shifts associated with the plasma flow, systemic velocity, and optical depth, we concluded that the major contributor to the observed redshift is the gravitational redshift of the WD harbored in the binary system, which is the first gravitational redshift detection from a magnetic WD. Moreover, the gravitational redshift provides us with a new method of the WD mass measurement by invoking the plasma-flow theory with strong magnetic fields in close binaries. Regardless of large uncertainty, our new method estimated the WD mass to be $M_{\rm WD}> 0.9\,M_{\odot}$.

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T. Hayashi, H. Mori, K. Mukai, et. al.
Wed, 3 May 23
14/67

Comments: 13 pages, 5 figures. Accepted for publication in ApJ

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

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]

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

Updated Inventory of Carbon Monoxide in The Taurus Molecular Cloud [GA]

http://arxiv.org/abs/2305.01112


The most extensive survey of carbon monoxide (CO) gas in the Taurus molecular cloud relied on $^{12}$CO and $^{13}$CO $J=1 \rightarrow 0$ emission only, distinguishing the region where $^{12}$CO is detected without $^{13}$CO (named mask 1 region) from the one where both are detected (mask 2 region). We have taken advantage of recent $^{12}$CO $J=3\rightarrow2$ JCMT observations where they include mask 1 regions to estimate density, temperature, and $N$(CO) with a LVG model. This represents 1395 pixels out of $\sim$1.2 million in the mark 1 region. Compared to Pineda et al. (2010) results, and assuming a $T_\textrm{kin}$ of 30 K, we find a higher volume density of molecular hydrogen of 3.3$\rm \times\ 10^3$ $\textrm{cm}^{-3}$, compared to their 250–700 $\textrm{cm}^{-3}$ and a CO column density of 5.7$\rm \times\ 10^{15}\ \textrm{cm}^{-2}$, about a quarter of their value. The differences are important and show the necessity to observe several CO transitions to better describe the intermediate region between the dense cloud and the diffuse atomic medium. Future observations to extend the $^{12}$CO $J=3\rightarrow2$ mapping further away from the $^{13}$CO–detected region comprising mask 1 are needed to revisit our understanding of the diffuse portions of dark clouds.

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Y. Duan, D. Li, L. Pagani, et. al.
Wed, 3 May 23
29/67

Comments: Accepted for publication in Research in Astronomy and Astrophysics. 15 pages, 2 tables, 8 figures

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

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]

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]

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]

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

New 26P(p,γ)27S thermonuclear reaction rate and its astrophysical implication in rp-process [CL]

http://arxiv.org/abs/2305.00371


Accurate nuclear reaction rates for 26P(p,{\gamma})27S are pivotal for a comprehensive understanding of rp-process nucleosynthesis path in the region of proton-rich sulfur and phosphorus isotopes. However, large uncertainties still exist in the current rate of 26P(p,{\gamma})27S because of the lack of the nuclear mass and the energy level structure information of 27S. We reevaluate this reaction rate using the experimentally constrained 27S mass, together with the shell-model predicted level structure. It is found that the 26P(p,{\gamma})27S reaction rate is dominated by a direct-capture (DC) reaction mechanism despite the presence of three resonances at E = 1.104, 1.597, 1.777 MeV above the proton threshold in 27S. The new rate is overall smaller than the other previous rates from Hauser-Feshbach statistical model by at least one order of magnitude in the temperature range of X-ray burst interest. In addition, we consistently update the photodisintegration rate using the new 27S mass. The influence of new rates of forward and reverse reaction in the abundances of isotopes produced in rp-process is explored by post-processing nucleosynthesis calculations. The final abundance ratio of 27S/26P obtained using the new rates is only 10% of that from the old rate. The abundance flow calculations show the reaction path 26P(p,{\gamma})27S(\b{eta}+,{\nu})27P is not as important as thought previously for producing 27P. The adoption of the new reaction rates for 26P(p,{\gamma})27S only reduces the final production of aluminum by 7.1%, and has no discernible impact on the yield of other elements.

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S. Hou, J. Liu, T. Trueman, et. al.
Tue, 2 May 23
3/57

Comments: N/A

DT fusion through the $^5$He $3/2+$ "Bretscher state" accounts for $\ge 25\%$ of our existence via nucleosynthesis and for the possibility of fusion energy [CL]

http://arxiv.org/abs/2305.00647


In big bang nucleosynthesis (BBN), the deuterium-tritium (DT) fusion reaction, D(T,n)$\alpha$, enhanced by the 3/2$^+$ resonance, is responsible for 99% of primordial $^4$He. This has been known for decades and has been well documented in the scientific literature. However, following the tradition adopted by authors of learned articles, it was stated in a matter-of-fact manner and not emphasized; for most people, it has remained unknown. This helium became a source for the subsequent creation of $\geq$25\% of the carbon and other heavier elements and, thus, a substantial fraction of our human bodies. (To be more precise than $\geq$25\% will require future simulation studies on stellar nucleosynthesis.)
Also, without this resonance, controlled fusion energy would be beyond reach. For example, for inertial confinement fusion (ICF), laser energy delivery for the National Ignition Facility (NIF) would have to be approximately 70 times larger for ignition.
Because the resonance enhances the DT fusion cross section a hundredfold, we propose that the 3/2$^+$ $^5$He excited state be referred to as the “Bretscher state” in honor of the Manhattan Project scientist who discovered it, in analogy with the well-known 7.6 MeV “Hoyle state” in $^{12}$C that allows for the resonant 3$\alpha$ formation.

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M. Chadwick, M. Paris and B. Haines
Tue, 2 May 23
4/57

Comments: 4 pages, 4 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]

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]

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]

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

Star-Planet Interaction at radio wavelengths in YZ Ceti: Inferring planetary magnetic field [EPA]

http://arxiv.org/abs/2305.00809


In exoplanetary systems, the interaction between the central star and the planet can trigger Auroral Radio Emission (ARE), due to the Electron Cyclotron Maser mechanism. The high brightness temperature of this emission makes it visible at large distances, opening new opportunities to study exoplanets and to search for favourable conditions for the development of extra-terrestrial life, as magnetic fields act as a shield that protects life against external particles and influences the evolution of the planetary atmospheres. In the last few years, we started an observational campaign to observe a sample of nearby M-type stars known to host exoplanets with the aim to detect ARE. We observed YZ Ceti with the upgraded Giant Metrewave Radio Telescope (uGMRT) in band 4 (550-900 MHz) nine times over a period of five months. We detected radio emission four times, two of which with high degree of circular polarization. With statistical considerations we exclude the possibility of flares due to stellar magnetic activity. Instead, when folding the detections to the orbital phase of the closest planet YZ Cet b, they are at positions where we would expect ARE due to star-planet interaction (SPI) in sub-Alfvenic regime. With a degree of confidence higher than 4.37 sigma, YZ Cet is the first extrasolar systems with confirmed SPI at radio wavelengths. Modelling the ARE, we estimate a magnetic field for the star of about 2.4 kG and we find that the planet must have a magnetosphere. The lower limit for the polar magnetic field of the planet is 0.4 G.

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C. Trigilio, A. Biswas, P. Leto, et. al.
Tue, 2 May 23
13/57

Comments: 11 pages, 7 figures, submitted to ApJ Letters in March 2023

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

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]

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]

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

SHAMPOO: A stochastic model for tracking dust particles under the influence of non-local disk processes [EPA]

http://arxiv.org/abs/2305.00861


The abundances of CHNOS are crucial for the composition of planets. At the onset of planet formation, large amounts of these elements are stored in ices on dust grains in planet-forming disks. The evolution of this ice is affected by dynamical transport, collisional processes, and the formation and sublimation of ice. We aim to constrain the disk regions where these processes are fully coupled, and develop a flexible modelling approach that is able to predict the effects of these processes acting simultaneously on the CHNOS budgets of the dust in these regions. We compared timescales associated with these disk processes to constrain the disk regions where this approach is necessary, and developed the SHAMPOO code, which tracks the CHNOS abundances in the ice mantle of a single monomer dust particle, embedded in a larger aggregate and undergoing these processes simultaneously. The adsorption and photodesorption of monomer ices depend on the depth of the monomer in the aggregate. We investigated the effect of fragmentation velocity and aggregate filling factor on the amount of ice on monomers residing at r = 10 AU. The locations where disk processes are fully coupled depend on both grain size and ice species. Monomers embedded in aggregates with fragmentation velocities of 1 m/s are able to undergo adsorption and photodesorption more often compared to a fragmentation velocity of 5 m/s or 10 m/s. Aggregates with a filling factor of $10^{-3}$ are able to accumulate ice 22 times faster on average than aggregates with a filling factor of 1. As different grain sizes are coupled through collisions and the grain ice consists of multiple ice species, it is difficult to isolate the locations where disk processes are fully coupled, necessitating the development of the SHAMPOO code. The processing of ice may not be spatially limited to dust aggregate surfaces for either fragile or porous aggregates.

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M. Oosterloo, I. Kamp, W. Westrenen, et. al.
Tue, 2 May 23
22/57

Comments: 30 pages, 24 figures, 4 tables, to appear in Astronomy & Astrophysics

Kinematics and stability of high-mass protostellar disk candidates at sub-arcsecond resolution — Insights from the IRAM NOEMA large program CORE [GA]

http://arxiv.org/abs/2305.00020


The fragmentation mode of high-mass molecular clumps and the accretion processes that form the most massive stars ($M\gtrsim 8M_\odot$) are still not well understood. To this end, we have undertaken a large observational program (CORE) making use of interferometric observations from the Northern Extended Millimetre Array (NOEMA) for a sample of 20 luminous ($L>10^4L_\odot$) protostellar objects in the 1.37 mm wavelength regime in both continuum and line emission, reaching $\sim$0.4″ resolution (800 au at 2 kpc). Using the dense gas tracer CH$3$CN, we find velocity gradients across 13 cores perpendicular to the directions of bipolar molecular outflows, making them excellent disk candidates. Specific angular momentum ($j$) radial profiles are on average $\sim10^{-3}$ km /s pc and follow $j \propto r^{1.7}$, consistent with a poorly resolved rotating and infalling envelope/disk model. Fitting the velocity profiles with a Keplerian model, we find protostellar masses in the range of $\sim 10-25$ $M\odot$. Modelling the level population of CH$_3$CN lines, we present temperature maps and find median gas temperatures in the range $70-210$ K. We create Toomre $Q$ maps to study the stability of the disks and find almost all (11 of 13) disk candidates to be prone to fragmentation due to gravitational instabilities at the scales probed by our observations. In particular, disks with masses greater than $\sim10-20\%$ of the mass of their host (proto)stars are Toomre unstable, and more luminous protostellar objects tend to have disks that are more massive and hence more prone to fragmentation. Our finings show that most disks around high-mass protostars are prone to disk fragmentation early in their formation due to their high disk to stellar mass ratio. This impacts the accretion evolution of high-mass protostars which will have significant implications for the formation of the most massive stars.

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A. Ahmadi, H. Beuther, F. Bosco, et. al.
Tue, 2 May 23
31/57

Comments: 27 pages, 12 figures, 6 appendices – accepted for publication in Astronomy and Astrophysics

Stellar pulsations interfering with the transit light curve: configurations with false positive misalignment [EPA]

http://arxiv.org/abs/2305.00440


Asymmetric features in exoplanet transit light curves are often interpreted as a gravity darkening effect especially if there is spectroscopic evidence of a spin-orbit misalignment. Since other processes can also lead to light curve asymmetries this may lead to inaccurate gravity darkening parameters. Here we investigate the case of non-radial pulsations as possible sources of asymmetry and likely source of misinterpreted parameters through simulations. We obtained a series of simulated transit light curves of a hypothetical exoplanet-star system: a host star with no gravity darkening exhibiting small amplitude pulsations, and a typical hot Jupiter in a circular, edge-on orbit. A number of scenarios of pulsations of various amplitudes were considered, and a proper account of the obscuring effect of transits on all the surface intensity components was made. The magnitude of amplitude and phase modulations of nonradial pulsations during transits was also also investigated. We then fitted both a non-gravity-darkened, and a gravity-darkened, free spin-orbit axis model on the data. The Akaike and Bayesian Information Criteria were used for an objective selection of the most plausible model. We then explored the dependence of the parameter deviations on the pulsation properties, in order to identify configurations that can lead to falsely misaligned solutions. Low-amplitude pulsations in general do not affect the determination of the system parameters beyond their noise nature. However, frequencies close to multiples of the orbital frequency are found to cause distortions leading to solutions with a side tilted stellar rotational axis, they are therefore preferable to clean beforehand for the sake of a correct analysis. Additionally, for cases with higher-amplitude pulsations, it is recommended to pre-process and clean the pulsations before analysis.

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A. Bókon, S. Kálmán, I. Bíró, et. al.
Tue, 2 May 23
37/57

Comments: Accepted in A&A on 24 April 2023, 14 pages, 10 figures

High Tide or Riptide on the Cosmic Shoreline? A Water-Rich Atmosphere or Stellar Contamination for the Warm Super-Earth GJ~486b from JWST Observations [EPA]

http://arxiv.org/abs/2305.00868


Planets orbiting M-dwarf stars are prime targets in the search for rocky exoplanet atmospheres. The small size of M dwarfs renders their planets exceptional targets for transmission spectroscopy, facilitating atmospheric characterization. However, it remains unknown whether their host stars’ highly variable extreme-UV radiation environments allow atmospheres to persist. With JWST, we have begun to determine whether or not the most favorable rocky worlds orbiting M dwarfs have detectable atmospheres. Here, we present a 2.8-5.2 micron JWST NIRSpec/G395H transmission spectrum of the warm (700 K, 40.3x Earth’s insolation) super-Earth GJ 486b (1.3 R${\oplus}$ and 3.0 M${\oplus}$). The measured spectrum from our two transits of GJ 486b deviates from a flat line at 2.2 – 3.3 $\sigma$, based on three independent reductions. Through a combination of forward and retrieval models, we determine that GJ 486b either has a water-rich atmosphere (with the most stringent constraint on the retrieved water abundance of H2O > 10% to 2$\sigma$) or the transmission spectrum is contaminated by water present in cool unocculted starspots. We also find that the measured stellar spectrum is best fit by a stellar model with cool starspots and hot faculae. While both retrieval scenarios provide equal quality fits ($\chi^2_\nu$ = 1.0) to our NIRSpec/G395H observations, shorter wavelength observations can break this degeneracy and reveal if GJ 486b sustains a water-rich atmosphere.

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S. Moran, K. Stevenson, D. Sing, et. al.
Tue, 2 May 23
41/57

Comments: 18 pages, 7 figures, 5 tables. Accepted in ApJ Letters. Co-First Authors

Hydrodynamic mixing of accretion disk outflows in collapsars: implications for r-process signatures [HEAP]

http://arxiv.org/abs/2305.00056


The astrophysical environments capable of triggering heavy-element synthesis via rapid neutron capture (the r-process) remain uncertain. While binary neutron star mergers (NSMs) are known to forge r-process elements, certain rare supernovae (SNe) have been theorized to supplement, or even dominate, r-production by NSMs. However, the most direct evidence for such SNe, unusual reddening of the emission caused by the high opacities of r-process elements, has not been observed. Recent work identified the distribution of r-process material within the SN ejecta as a key predictor of the ease with which signals associated with r-process enrichment could be discerned. Though this distribution results from hydrodynamic processes at play during the SN explosion, thus far it has been treated only in a parameterized way. We use hydrodynamic simulations to model how disk winds, the alleged locus of r-production in rare SNe, mix with initially r-process-free ejecta. We study mixing as a function of the wind mass and duration and of the initial SN explosion energy, and find that it increases with the first two of these and decreases with the third. This suggests that SNe accompanying the longest long-duration gamma-ray bursts are promising places to search for signs of r-process enrichment. We use semianalytic radiation transport to connect hydrodynamics to electromagnetic observables, allowing us to assess the mixing level at which the presence of r-process material can be diagnosed from SN light curves. Analytic arguments constructed atop this foundation imply that a wind-driven r-process-enriched SN model is unlikely to explain standard energetic SNe.

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J. Barnes and P. Duffell
Tue, 2 May 23
49/57

Comments: Submitted to ApJ. Comments welcome

The rocket effect mechanism in neutron stars in supernova remnants [HEAP]

http://arxiv.org/abs/2305.00025


While the dipole magnetic field axis of neutron stars is usually postulated to cross the star’s centre, it may be displaced from this location, as it has been recently indicated in the millisecond pulsar J0030+0451. Under these conditions, the electromagnetic rocket effect may be activated, where the magnetic field exerts a net force, accelerating the star. This post-natal kick mechanism relies on asymmetric electromagnetic radiation from an off-centre dipole may be relevant to the high spatial velocities of pulsars $\sim 10^{3}$ $\rm{km/s}$. Here, we explore its impact in young pulsars associated with supernova remnants and we compare the observational data on characteristic quantities, such as the braking index and proper motion, with results obtained from the rocket effect. Using a Markov Chain Monte Carlo analysis, we explore the required conditions, for the initial spin periods and the distance between the magnetic axis and the star’s center, so that the velocity kick due to the rocket effect approaches the present velocity. We find that the electromagnetic rocket effect can account for typical pulsar transverse velocities assuming an initial spin period of 3.8 $\rm{ms}$ and a dipole field whose distance from the centre of the star is approximately 7 $\rm{km}$. We also explore the influence of the rocket effect on the braking index of a neutron star, and we find that for the sample studied this impact is minimal. Finally, we apply the rocket effect model on the pulsars J0030+0451 and J0538+2817, which are likely candidates for this mechanism.

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V. Agalianou and K. Gourgouliatos
Tue, 2 May 23
54/57

Comments: N/A

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

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

Gravitational waves from non-radial perturbations in glitching pulsars [CL]

http://arxiv.org/abs/2304.14644


The Rossby mode (r-mode) perturbations in pulsars as a steady gravitational wave (GW) sources have been explored. The time evolution and the intensity of the emitted GWs in terms of the strain tensor amplitude have been estimated with the approximation of slow rotation adopting the equation of state derived using the Skyrme effective interaction with NRAPR parameter set. The core of the neutron star has been considered to be $\beta$-equilibrated nuclear matter composed of neutrons, protons, electrons and muons, which is surrounded by a solid crust. Calculations have been made for the critical frequencies, the evolution of frequencies and frequency change rates with time as well as the fiducial viscous and gravitational timescales, across a broad spectrum of pulsar masses. Our findings reveal that the r-mode instability region is associated with rotating young and hot pulsars. Furthermore, it is noteworthy that pulsars with low $L$ value emit gravitational radiation and fall within the r-mode instability region if the primary dissipative mechanism is shear viscosity along the crust-core interface boundary layer. The r-mode perturbation amplitude increases because of GW emissions, in contrast to other non-radial perturbations which transport to infinity the star’s angular momentum. Thus the presence of these stellar perturbations implies a non-negative rate of change in transfer of rotational angular momentum. This observation suggests that for a glitching pulsar, the GW emission intensity evolves increasingly with time till the angular frequency diminishes to a value that is below a crucial threshold, after which the compact star ceases to emit radiation.

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J. Lahiri and D. Basu
Mon, 1 May 23
3/51

Comments: 15 pages including 15 figures and 2 tables

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

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]

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]

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]

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]

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]

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]

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]

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]

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]

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

Oscillations in Gas-grain Astrochemical Kinetics [GA]

http://arxiv.org/abs/2304.14428


We have studied gas-grain chemical models of interstellar clouds to search for nonlinear dynamical evolution. A prescription is given for producing oscillatory solutions when a bistable solution exists in the gas-phase chemistry and we demonstrate the existence of limit cycle and relaxation oscillation solutions. As the autocatalytic chemical processes underlying these solutions are common to all models of interstellar chemistry, the occurrence of these solutions should be widespread. We briefly discuss the implications for interpreting molecular cloud composition with time-dependent models and some future directions for this approach.

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G. Dufour, S. Charnley and J. Lindberg
Mon, 1 May 23
38/51

Comments: 9 pages, 3 figures, 1 table

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

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]

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]

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

Gas distribution in ODISEA sources from ALMA long-baseline observations in $^{12}$CO(2-1) [EPA]

http://arxiv.org/abs/2304.15002


The $^{12}$CO rotational lines in protoplanetary discs are good tracers of the total spatial extension of the gas component, and potentially planet-disc interactions. We present ALMA long baseline observations of the $^{12}$CO(2-1) line of ten protoplanetary discs from the Ophiuchus DIsc Survey Employing ALMA (ODISEA) project, aiming to set constraints on the gas distribution of these sources. The position angle of the gaseous disc can be inferred for five sources using high-velocity channels, which trace the gas in the inner part of the disc. We compare the high-velocity PAs to the orientations inferred from the continuum, representative of the orientation over $\sim$ 53 to 256 au in these resolved discs. We find a significant difference in orientation for DoAr 44, which is evidence of a tilted inner disc. Eight discs show evidence of gas inside inner dust cavities or gaps, and the disc of ISO-Oph 196 is not detected in $^{12}$CO(2-1), except for the compact signal located inside its dust cavity. Our observations also point out a possible outflow in WLY 2-63.

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J. Antilen, S. Casassus, L. Cieza, et. al.
Mon, 1 May 23
45/51

Comments: N/A

New Bistable Solutions in Molecular Cloud Chemistry: Nitrogen and Carbon Autocatalysis [GA]

http://arxiv.org/abs/2304.14477


We have investigated the chemistry of dense interstellar clouds and found new bistable solutions in the nitrogen and carbon chemistries. We identify the autocatalytic processes that are present in the pure, reduced, chemical networks and, as previously found for oxygen chemistry, that He$^+$ plays an important role.
The applicability of these results to astronomical environments is briefly discussed. The bistable solutions found for carbon chemistry occur for low densities and high ionization fractions that are not compatible with that found cold, dense clouds. Bistability in the pure nitrogen chemistry occurs for conditions that are relevant for prestellar cores in which significant CO depletion has taken place. We conclude that several autocatalyses are embedded in gas-phase interstellar chemistry and that many more are potentially present.

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D. Gwenaëlle and S. Charnley
Mon, 1 May 23
48/51

Comments: 12 pages, 5 figures, 1 table

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]

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

Combined analysis of stellar and planetary absorption lines via global forward-transit simulations [EPA]

http://arxiv.org/abs/2304.13759


We characterise the planet-occulted line distortions (POLDs) in absorption spectra of transiting planets, that arise from proxies used for the occulted stellar lines and investigate the impact of stellar rotation, centre-to-limb variations, and broadband limb-darkening. We used the EVaporating Exoplanets (EVE) code to generate realistic stellar spectra during the transit of exoplanets, accounting for the 3D geometry of the system’s architecture and atmospheric transit, as well as for spectral variations over the stellar disc. The absorption spectra were calculated using approaches drawn from the literature and compared to the expected signal. The POLDs from stellar rotation are dominant for moderate to fast rotating stars, reaching amplitudes comparable to atmospheric signals, but they can be mitigated by shifting the stellar line proxies to the radial velocity of the planet-occulted region. Centre-to-limb variations become dominant for slow rotators and are more easily mitigated at the stellar limb. We re-interpret the ESPRESSO data of two iconic systems and confirm that the sodium signature from HD209458b mainly arises from POLDs. However, we unveil a possible contribution from the planetary atmosphere that warrants further observations. For MASCARA-1b, we did not find evidence for atmospheric sodium absorption and we can fully explain the observed signature by a POLD for super-solar stellar sodium abundance. We studied POLDs dependency on star and planet properties, and on the proxy used for planet-occulted lines. Distinguishing planetary absorption signatures from POLDs is challenging without access to accurate estimates of the local stellar spectrum and system orbital parameters. We propose a way to mitigate POLDs and improve atmospheric characterisation, by using simultaneous forward modelling of both the star and the planet to simulate the global observed signatures.

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W. Dethier and V. Bourrier
Fri, 28 Apr 23
6/68

Comments: N/A

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

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]

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

IDEFIX: a versatile performance-portable Godunov code for astrophysical flows [IMA]

http://arxiv.org/abs/2304.13746


Exascale super-computers now becoming available rely on hybrid energy-efficient architectures that involve an accelerator such as Graphics Processing Units (GPU). Leveraging the computational power of these machines often means a significant rewrite of the numerical tools each time a new architecture becomes available. To address these issues, we present Idefix, a new code for astrophysical flows that relies on the Kokkos meta-programming library to guarantee performance portability on a wide variety of architectures while keeping the code as simple as possible for the user. Idefix is based on a Godunov finite-volume method that solves the non-relativistic HD and MHD equations on various grid geometries. Idefix includes a wide choice of solvers and several additional modules (constrained transport, orbital advection, non-ideal MHD) allowing users to address complex astrophysical problems. Idefix has been successfully tested on Intel and AMD CPUs (up to 131 072 CPU cores on Irene-Rome at TGCC) as well as NVidia and AMD GPUs (up to 1024 GPUs on Adastra at CINES). Idefix achieves more than 1e8 cell/s in MHD on a single NVidia V100 GPU and 3e11 cell/s on 256 Adastra nodes (1024 GPUs) with 95% parallelization efficiency (compared to a single node). For the same problem, Idefix is up to 6 times more energy efficient on GPUs compared to Intel Cascade Lake CPUs. Idefix is now a mature exascale-ready open-source code that can be used on a large variety of astrophysical and fluid dynamics applications.

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G. Lesur, S. Baghdadi, G. Wafflard-Fernandez, et. al.
Fri, 28 Apr 23
20/68

Comments: 18 pages, 18 figures, 3 tables, accepted for publication in Astronomy & Astrophysics

Applied Machine-Learning Models to Identify Spectral Sub-Types of M Dwarfs from Photometric Surveys [IMA]

http://arxiv.org/abs/2304.14113


M dwarfs are the most abundant stars in the Solar Neighborhood and they are prime targets for searching for rocky planets in habitable zones. Consequently, a detailed characterization of these stars is in demand. The spectral sub-type is one of the parameters that is used for the characterization and it is traditionally derived from the observed spectra. However, obtaining the spectra of M dwarfs is expensive in terms of observation time and resources due to their intrinsic faintness. We study the performance of four machine-learning (ML) models: K-Nearest Neighbor (KNN), Random Forest (RF), Probabilistic Random Forest (PRF), and Multilayer Perceptron (MLP), in identifying the spectral sub-types of M dwarfs at a grand scale by deploying broadband photometry in the optical and near-infrared. We trained the ML models by using the spectroscopically identified M dwarfs from the Sloan Digital Sky Survey Data Release (SDSS) 7, together with their photometric colors that were derived from the SDSS, Two-Micron All-Sky Survey, and Wide-field Infrared Survey Explorer. We found that the RF, PRF, and MLP give a comparable prediction accuracy, 74%, while the KNN provides slightly lower accuracy, 71%. We also found that these models can predict the spectral sub-type of M dwarfs with ~99% accuracy within +/-1 sub-type. The five most useful features for the prediction are r-z, r-i, r-J, r-H, and g-z, and hence lacking data in all SDSS bands substantially reduces the prediction accuracy. However, we can achieve an accuracy of over 70% when the r and i magnitudes are available. Since the stars in this study are nearby (d~1300 pc for 95% of the stars), the dust extinction can reduce the prediction accuracy by only 3%. Finally, we used our optimized RF models to predict the spectral sub-types of M dwarfs from the Catalog of Cool Dwarf Targets for TESS, and we provide the optimized RF models for public use.

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S. Sithajan and S. Meethong
Fri, 28 Apr 23
22/68

Comments: 17 pages, 7 figures, 6 tables, Accepted for publication in PASP

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

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

Chemical Differentiation around Five Massive Protostars Revealed by ALMA -Carbon-Chain Species, Oxygen-/Nitrogen-Bearing Complex Organic Molecules- [GA]

http://arxiv.org/abs/2304.13873


We present Atacama Large Millimeter/submillimeter Array Band 3 data toward five massive young stellar objects (MYSOs), and investigate relationships between unsaturated carbon-chain species and saturated complex organic molecules (COMs). An HC${5}$N ($J=35-34$) line has been detected from three MYSOs, where nitrogen(N)-bearing COMs (CH${2}$CHCN and CH${3}$CH${2}$CN) have been detected. The HC${5}$N spatial distributions show compact features and match with a methanol (CH${3}$OH) line with an upper-state energy around 300 K, which should trace hot cores. The hot regions are more extended around the MYSOs where N-bearing COMs and HC${5}$N have been detected compared to two MYSOs without these molecular lines, while there are no clear differences in the bolometric luminosity and temperature. We run chemical simulations of hot-core models with a warm-up stage, and compare with the observational results. The observed abundances of HC${5}$N and COMs show good agreements with the model at the hot-core stage with temperatures above 160 K. These results indicate that carbon-chain chemistry around the MYSOs cannot be reproduced by warm carbon-chain chemistry, and a new type of carbon-chain chemistry occurs in hot regions around MYSOs.

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K. Taniguchi, L. Majumdar, P. Caselli, et. al.
Fri, 28 Apr 23
24/68

Comments: Accepted by the publication for The Astrophysical Journal Supplement Series, 32 pages,18 figures, 11 tables

Stellar wind variability in Cygnus X-1 from high-resolution excess variance spectroscopy with Chandra [HEAP]

http://arxiv.org/abs/2304.14201


Stellar winds of massive stars are known to be driven by line absorption of UV photons, a mechanism which is prone to instabilities, causing the wind to be clumpy. The clumpy structure hampers wind mass-loss estimates, limiting our understanding of massive star evolution. The wind structure also impacts accretion in high-mass X-ray binary (HMXB) systems. We analyse the wavelength-dependent variability of X-ray absorption in the wind to study its structure. Such an approach is possible in HMXBs, where the compact object serves as an X-ray backlight. We probe different parts of the wind by analysing data taken at superior and inferior conjunction. We apply excess variance spectroscopy to study the wavelength-dependent soft X-ray variability of the HMXB Cygnus X-1 in the low/hard spectral state. Excess variance spectroscopy quantifies the variability of an object above the statistical noise as a function of wavelength, which allows us to study the variability of individual spectral lines. As one of the first studies, we apply this technique to high-resolution gratings spectra provided by Chandra, accounting for various systematic effects. The frequency dependence is investigated by changing the time binning. The strong orbital phase dependence we observe in the excess variance is consistent with column density variations predicted by a simple model for a clumpy wind. We identify spikes of increased variability with spectral features found by previous spectroscopic analyses of the same data set, most notably from silicon in over-dense clumps in the wind. In the silicon line region, the variability power is redistributed towards lower frequencies, hinting at increased line variability in large clumps. In prospect of the microcalorimetry missions that are scheduled to launch within the next decade, excess variance spectra present a promising approach to constrain the wind structure.

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L. Härer, M. Parker, I. Mellah, et. al.
Fri, 28 Apr 23
29/68

Comments: Submitted to A&A

Sodium enhancement in evolved CVs [SSA]

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

Thermal Tomography of the Inner Regions of Protoplanetary Disks with the ngVLA and ALMA [EPA]

http://arxiv.org/abs/2304.14192


Understanding the temperature structure of protoplanetary disks is crucial for answering the fundamental question of when and where in the disks rocky planets like our own form. However, the thermal structure of the inner few au of the disks is poorly understood not only because of lack of observational constraints but also because of the uncertainty of accretion heating processes. Here, we propose thermal tomography of the inner regions of protoplanetary disks with the ngVLA and ALMA. The proposed approach is based on the assumption that the inner disk regions are optically thick at submillimeter wavelengths but are marginally optically thin at longer millimeter wavelengths. By combining high-resolution millimeter continuum images from the ngVLA with submillimeter images at comparable resolutions from ALMA, we will be able to reconstruct the radial and vertical structure of the inner few au disk regions. We demonstrate that the thermal tomography we propose can be used to constrain the efficiency of midplane accretion heating, a process that controls the timing of snow-line migration to the rocky planet-forming region, in the few au regions of protoplanetary disks at a distance of 140 pc.

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S. Okuzumi, M. Momose and A. Kataoka
Fri, 28 Apr 23
36/68

Comments: 4 pages, 3 figures, ngVLA-Japan Memo Series P006 (2021), this https URL

Spiral wave driven accretion in quiescent dwarf novæ [HEAP]

http://arxiv.org/abs/2304.13773


In dwarf nov{\ae} and low-mass X-ray binaries, the tidal potential excites spiral waves in the accretion disc. Spiral wave driven accretion may be important in quiescent discs, where the angular momentum transport mechanism has yet to be identified. Previous studies were limited to unrealistically high temperatures for numerical studies or to specific regimes for analytical studies. We perform the first numerical simulation of spiral wave driven accretion in the cold temperature regime appropriate to quiescent discs, which have Mach numbers > 100. We use the new GPU-accelerated finite volume code Idefix to produce global hydrodynamics 2D simulations of the accretion discs of dwarf nov{\ae} systems with a fine-enough spatial resolution to capture the short scale-height of cold, quiescent discs with Mach numbers ranging from 80 to 370. Running the simulations on timescales of tens of binary orbits shows transient angular momentum transport that decays as the disc relaxes from its initial conditions. We find the angular momentum parameter {\alpha} drops to values << 0.01 , too weak to drive accretion in quiescence.

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M. Bossche, G. Lesur and G. Dubus
Fri, 28 Apr 23
40/68

Comments: N/A

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

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]

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]

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]

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

Removing Aliases in Time-Series Photometry [EPA]

http://arxiv.org/abs/2304.13843


Ground-based, all-sky astronomical surveys are imposed with an inevitable day-night cadence that can introduce aliases in period-finding methods. We examined four different methods — three from the literature and a new one that we developed — that remove aliases to improve the accuracy of period-finding algorithms. We investigate the effectiveness of these methods in decreasing the fraction of aliased period solutions by applying them to the Zwicky Transient Facility (ZTF) and the LSST Solar System Products Data Base (SSPDB) asteroid datasets. We find that the VanderPlas method had the worst accuracy for each survey. The mask and our newly proposed window method yields the highest accuracy when averaged across both datasets. However, the Monte Carlo method had the highest accuracy for the ZTF dataset, while for SSPDB, it had lower accuracy than the baseline where none of these methods are applied. Where possible, detailed de-aliasing studies should be carried out for every survey with a unique cadence.

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D. Kramer, M. Gowanlock, D. Trilling, et. al.
Fri, 28 Apr 23
67/68

Comments: N/A

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

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]

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]

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]

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]

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]

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

A moderate spin for the black hole in X-ray binary MAXI J1348-630 revealed by Insight-HXMT [HEAP]

http://arxiv.org/abs/2304.13285


MAXI J1348-630 is a low-mass X-ray black hole binary located in the Galaxy and undergone the X-ray outburst in 2019. We analyzed the observation data in very soft state during the outburst between MJD 58588 and MJD 58596 based on the Insight-HXMT observations from 2 — 20 keV via the continuum fitting method to measure the spin of the stellar-mass black hole in MAXI J1348-630. The inner disk temperature and the apparent inner disk radius were found to be $0.47\pm 0.01 \rm keV$ and $5.33\pm 0.10 \ R_{g}$ from the observation data modeled by the multicolor disc blackbody model. Assuming the distance of the source $D\sim 3.4 \rm kpc$, the mass of the black hole $M\sim 11 \ M_{\odot}$, and the inclination of the system $i\sim 29.2^{\circ}$, the spin is determined to be $a_{\star}=0.41\pm 0.03$ for fixing hardening factor at 1.6 and $n_{H}=8.6\times 10^{21} \rm cm^{-2}$. Besides, considering the uncertainty of the parameters $D, M, i$ of this system, with the Monte Carlo analysis, we still confirm the moderate spin of the black hole as $a_{\star}=0.42^{+0.13}_{-0.50}$. Some spectral parameters (e.g., column density and hardening factor) which could affect the measurements of the BH spin are also briefly discussed.

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H. Wu, W. Wang, N. Sai, et. al.
Thu, 27 Apr 23
19/78

Comments: 10 pages, 14 figures, 5 tables, accept for publication in MNRAS

Multi-Epoch Spectropolarimetry for a Sample of Type IIn Supernovae: Persistent Asymmetry in Dusty Circumstellar Material [HEAP]

http://arxiv.org/abs/2304.13034


We present multi-epoch spectropolarimetry and spectra for a sample of 14 Type IIn supernovae (SNe IIn). We find that after correcting for likely interstellar polarization, SNe IIn commonly show intrinsic continuum polarization of 1–3% at the time of peak optical luminosity, although a few show weaker or negligible polarization. While some SNe IIn have even stronger polarization at early times, their polarization tends to drop smoothly over several hundred days after peak. We find a tendency for the intrinsic polarization to be stronger at bluer wavelengths, especially at early times. While polarization from an electron scattering region is expected to be grey, scattering of SN light by dusty circumstellar material (CSM) may induce such a wavelength-dependent polarization. For most SNe IIn, changes in polarization degree and wavelength dependence are not accompanied by changes in the position angle, requiring that asymmetric pre-SN mass loss had a persistent geometry. While 2–3% polarization is typical, about 30% of SNe IIn have very low or undetected polarization. Under the simplifying assumption that all SN IIn progenitors have axisymmetric CSM (i.e. disk/torus/bipolar), then the distribution of polarization values we observe is consistent with similarly asymmetric CSM seen from a distribution of random viewing angles. This asymmetry has very important implications for understanding the origin of pre-SN mass loss in SNe IIn, suggesting that it was shaped by binary interaction.

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C. Bilinski, N. Smith, G. Williams, et. al.
Thu, 27 Apr 23
20/78

Comments: 76 pages, 54 figures (13 in main text, 41 in appendix A)

Impact of turbulence intensity and fragmentation velocity on dust particle size evolution and non-ideal magnetohydrodynamics effects [GA]

http://arxiv.org/abs/2304.13271


We investigate the influence of dust particle size evolution on non-ideal magnetohydrodynamic effects during the collapsing phase of star-forming cores, taking both the turbulence intensity in the collapsing cloud core and the fragmentation velocity of dust particles as parameters. When the turbulence intensity is small, the dust particles do not grow significantly, and the non-ideal MHD effects work efficiently in high-density regions. The dust particles rapidly grow in a strongly turbulent environment, while the efficiency of non-ideal MHD effects in such an environment depends on the fragmentation velocity of the dust particles. When the fragmentation velocity is small, turbulence promotes coagulation growth and collisional fragmentation of dust particles, producing small dust particles. In this case, the adsorption of charged particles on the dust particle surfaces becomes efficient and the abundance of charged particles decreases, making non-ideal MHD effects effective at high densities. On the other hand, when the fragmentation velocity is high, dust particles are less likely to fragment, even if the turbulence is strong. In this case, the production of small dust particles become inefficient and non-ideal MHD effects become less effective. We also investigate the effect of the dust composition on the star and disk formation processes. We constrain the turbulence intensity of a collapsing core and the fragmentation velocity of dust for circumstellar disk formation due to the dissipation of the magnetic field.

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Y. Kawasaki and M. Machida
Thu, 27 Apr 23
22/78

Comments: Accepted for publication in MNRAS. 15 pages, 13 figures

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

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]

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)

Measurements of spin and orbital parameters in Cen X-3 by Insight-HXMT [HEAP]

http://arxiv.org/abs/2304.13279


We present a detailed temporal analysis for the eclipsing high-mass X-ray binary system Cen X-3 using the Insight-HXMT data in 2018 and 2020. Three consecutive and high statistic observations among data are used for the precise timing analysis. The pulse profiles are revealed to vary with energy and time. The pulse profiles for the 2018 observations showed a double peak in the low energy bands below 10 keV and evolved to a single peak in higher energies without the correlation between pulse fraction and flux, and profiles in low energies changed with time. But the pulse profile for the 2020 observation only showed a broad single-peaked pulse in all energy bands with a positive relation between pulse fraction and flux, which may indicate the transition of the emission patterns from a mixture of a pencil and a fan beam to a dominated pencil-like beam. With performing a binary orbital fitting of spin periods, we obtain an accurate value for the spin period and the orbital parameters. The intrinsic spin period of the neutron star is found to be $4.79920 \pm 0.00006$ s at MJD 58852.697, with the orbital period determined at $P_{\rm orb}=2.08695634\pm 0.00000001$ day, and its decay rate of -(1.7832 $\pm$ 0.0001) $\times$ 10$^{-6}$ yr$^{-1}$ for the binary.

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Q. Liu and W. Wang
Thu, 27 Apr 23
34/78

Comments: 12 pages in the authors’ version, reference: Journal of High Energy Astrophysics, 38 (2023), 32-40

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

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

Narrow loophole for H2-dominated atmospheres on habitable rocky planets around M dwarfs [EPA]

http://arxiv.org/abs/2304.13659


Habitable rocky planets around M dwarfs that have H2-dominated atmospheres, if they exist, would permit characterizing habitable exoplanets with detailed spectroscopy using JWST, owing to their extended atmospheres and small stars. However, the H2-dominated atmospheres that are consistent with habitable conditions cannot be too massive, and a moderate-size H2-dominated atmosphere will lose mass to irradiation-driven atmospheric escape on rocky planets around M dwarfs. We evaluate volcanic outgassing and serpentinization as two potential ways to supply H2 and form a steady-state H2-dominated atmosphere. For rocky planets of 1-7 Earth mass and early, mid, and late M dwarfs, the expected volcanic outgassing rates from a reduced mantle fall short of the escape rates by >~1 order of magnitude, and a generous upper limit of the serpentinization rate is still less than the escape rate by a factor of a few. Special mechanisms that may sustain the steady-state H2-dominated atmosphere include direct interaction between liquid water and mantle, heat-pipe volcanism from a reduced mantle, and hydrodynamic escape slowed down by efficient upper-atmospheric cooling. It is thus unlikely to find moderate-size, H2-dominated atmospheres on rocky planets of M dwarfs that would support habitable environments.

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R. Hu, F. Gaillard and E. Kite
Thu, 27 Apr 23
47/78

Comments: Accepted for publication in ApJ Letters

Stars on the edge: Galactic tides and the outskirts of the Sculptor dwarf spheroidal [GA]

http://arxiv.org/abs/2304.13048


Stars far beyond the half-light radius of a galaxy suggest the existence of a mechanism able to move stars out of the region where most star formation has taken place. The formation of these “stellar halos” are usually ascribed to the effects of early mergers or Galactic tides, although fluctuations in the gravitational potential due to stellar feedback is also a possible candidate mechanism. A Bayesian algorithm is used to find new candidate members in the extreme outskirts of the Sculptor dwarf galaxy. Precise metallicities and radial velocities for two distant stars are measured from their spectra taken with the Gemini South GMOS spectrograph. The radial velocity, proper motion and metallicity of these targets are consistent with Sculptor membership. As a result, the known boundary of the Sculptor dwarf extends now out to an elliptical distance of $\sim10$ half-light radii, which corresponds to a projected physical distance of $\sim3$ kpc. As reported in earlier work, the overall distribution of radial velocities and metallicities indicate the presence of a more spatially and kinematically dispersed metal-poor population that surrounds the more concentrated and colder metal-rich stars. Sculptor’s density profile shows a “kink” in its logarithmic slope at a projected distance of $\sim25$ arcmin (620 pc), which we interpret as evidence that Galactic tides have helped to populate the distant outskirts of the dwarf. We discuss further ways to test and validate this tidal interpretation for the origin of these distant stars.

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F. Sestito, J. Roediger, J. Navarro, et. al.
Thu, 27 Apr 23
48/78

Comments: 10 pages, 4 figures, submitted to MNRAS

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

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]

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]

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

Accretion disk wind during the outburst of the stellar-mass black hole MAXI J1348-630 [HEAP]

http://arxiv.org/abs/2304.13281


We analyzed two observations of the low-mass black hole X-ray binary MAXI J1348-630 from Nuclear Spectroscopic Telescope Array (NuSTAR) during low hard state and hard intermediate state in the 2019 outburst. The reflection components are found in the X-ray spectra, and the spectral fittings give an inclination angle of $\sim 25^\circ-35^\circ$ for the binary system, and there is an absorption line around $\sim 7$ keV coming from highly ionized iron. The photoionization code XSTAR is used to fit the absorption line, which is attributed to outflows with a velocity of $\sim 10^{4}\rm km\ s^{-1}$ along our line of sight and the column density reaching $10^{23}\rm cm^{-2}$ in low hard and hard intermediate states. The physical mechanism launching fast disk winds from the black hole accretion system is still uncertain. These observations strongly support magnetic launching as the dominant mechanism which drives the high velocity, high ionization winds from the inner accretion disk region in hard and hard intermediate states of MAXI J1348-630.

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H. Wu, W. Wang and N. Sai
Thu, 27 Apr 23
66/78

Comments: 12 pages in the authors’ version, reference:Journal of High Energy Astrophysics, 37 (2023), 25-33

Relativistic Corrections in White Dwarf Asteroseismology [SSA]

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

Discovery of Two Cyclotron Resonance Scattering Features in X-ray Pulsar Cen X-3 by Insight-HXMT [HEAP]

http://arxiv.org/abs/2304.13283


We present the results of the neutron star X-ray binary system Cen X-3 performed by $Insight$-HXMT with two observations during 2017 and 2018. During these two observations, the source reached a X-ray luminosity of $\sim 10^{38}$ erg s$^{-1}$ from 2 — 105 keV. The analysis of the broadband X-ray spectrum reports the presence of two cyclotron resonance scattering features (CRSFs) with the fundamental line at $\sim$ 28 keV and the harmonic line at $\sim 47 $ keV. The multiple lines exist by fittings with different continuum models, like the absorbed NPEX model and a power-law with high energy exponential cutoff model. This is the first time that both fundamental and harmonic lines are detected in Cen X-3. We also show evidence of two cyclotron lines in the phase-resolved spectrum of Cen X-3. The CRSF and continuum spectral parameters show evolution with the pulse profile, and the two line centroid energy ratio does not change significantly and locates in a narrow value range of $1.6-1.7$ over the pulse phase. The implications of the discovering two cyclotron absorption features and phase-resolved spectral properties are discussed.

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W. Yang, W. Wang, Q. Liu, et. al.
Thu, 27 Apr 23
72/78

Comments: 8 pages, MNRAS, 2023, 519, 5402-5409

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

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

Modeling Two First Hydrostatic Core Candidates Barnard 1b-N and 1b-S [GA]

http://arxiv.org/abs/2304.12790


A first hydrostatic core (FHC) is proposed to form after the initial collapse of a prestellar core, as a seed of a Class 0 protostar. FHCs are difficult to observe because they are small, compact, embedded, and short lived. In this work, we explored the physical properties of two well-known FHC candidates, B1-bN and B1-bS, by comparing interferometric data from Submillimeter Array (SMA) 1.1 and 1.3 mm and Atacama Large Millimeter/submillimeter Array (ALMA) 870 $\mu$m observations with simulated synthesis images of the two sources. The simulated images are based on a simple model containing a single, hot compact first-core-like component at the center surrounded by a large-scale, cold and dusty envelope described by a broken power-law density distribution with an index, $\alpha$. Our results show that the hot compact components of B1-bN and B1-bS can be described by temperatures of \sim 500 K with a size of \sim 4 au, which are in agreement with theoretical predictions of an FHC. If the $\alpha$ inside the broken radii is fixed to -1.5, we find $\alpha$ \sim -2.9 and \sim -3.3 outside the broken radii for B1-bN and B1-bS, respectively, consistent with theoretical calculations of a collapsing, bounded envelope and previous observations. Comparing the density and temperature profiles of the two sources with radiation-hydrodynamic simulations of an FHC, we find both sources lie close to, but before, the second collapse stage. We suggest that B1-bS may have started the collapsing process earlier compared to B1-bN, since a larger discontinuity point is found in its density profile.

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H. Duan, S. Lai, N. Hirano, et. al.
Wed, 26 Apr 23
8/62

Comments: N/A

Population study on MHD wind-driven disc evolution — Confronting theory and observation [EPA]

http://arxiv.org/abs/2304.12380


Context. Current research has established magnetised disc winds as a promising way of driving accretion in protoplanetary discs. Aims. We investigate the evolution of large protoplanetary disc populations under the influence of magnetically driven disc winds as well as internal and external photoevaporation. We aim to constrain magnetic disc wind models through comparisons with observations. Methods. We ran 1D vertically integrated evolutionary simulations for low-viscosity discs, including magnetic braking and various outflows. The initial conditions were varied and chosen to produce populations that are representative of actual disc populations inferred from observations. We then compared the observables from the simulations (e.g. stellar accretion rate, disc mass evolution, disc lifetime, etc.) with observational data. Results. Our simulations show that to reach stellar accretion rates comparable to those found by observations $\sim 10^{-8}\mathrm{M}_\odot / \mathrm{yr}$, it is necessary to have access not only to strong magnetic torques, but weak magnetic winds as well. The presence of a strong magnetic disc wind, in combination with internal photoevaporation, leads to the rapid opening of an inner cavity early on, allowing the stellar accretion rate to drop while the disc is still massive. Furthermore, our model supports the notion that external photoevaporation via the ambient far-ultraviolet radiation of surrounding stars is a driving force in disc evolution and could potentially exert a strong influence on planetary formation. Conclusions. Our disc population syntheses show that for a subset of magnetohydrodynamic wind models (weak disc wind, strong torque), it is possible to reproduce important statistical observational constraints. The magnetic disc wind paradigm thus represents a novel and appealing alternative to the classical $\alpha$-viscosity scenario.

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J. Weder, C. Mordasini and A. Emsenhuber
Wed, 26 Apr 23
9/62

Comments: Accepted for publication in A&A

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

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]

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