Tag Archives: Solar and Stellar Astrophysics

Estimating Stellar Parameters from LAMOST Low-resolution Spectra [SSA]

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http://arxiv.org/abs/2303.15690


The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) has acquired tens of millions of low-resolution spectra of stars. This paper investigated the parameter estimation problem for these spectra. To this end, we proposed a deep learning model StarGRU network (StarGRUNet). This network was further applied to estimate the stellar atmospheric physical parameters and 13 elemental abundances from LAMOST low-resolution spectra. On the spectra with signal-to-noise ratios greater than or equal to $5$, the estimation precisions are $94$ K and $0.16$ dex on $T_\texttt{eff}$ and $\log \ g$ respectively, $0.07$ dex to $0.10$ dex on [C/H], [Mg/H], [Al/H], [Si/H], [Ca/H], [Ni/H] and [Fe/H], and $0.10$ dex to $0.16$ dex on [O/H], [S/H], [K/H], [Ti/H] and [Mn/H], and $0.18$ dex and $0.22$ dex on [N/H] and [Cr/H] respectively. The model shows advantages over available models and high consistency with high-resolution surveys. We released the estimated catalog computed from about 8.21 million low-resolution spectra in LAMOST DR8, code, trained model, and experimental data for astronomical science exploration and data processing algorithm research respectively.

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X. Li and B. Lin
Wed, 29 Mar 23
57/73

Comments: 15 pages, 12 figures, 3 tables, MNRAS

Ongoing hierarchical massive cluster assembly: the LISCA II structure in the Perseus complex [GA]

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http://arxiv.org/abs/2303.15501


We report on the identification of a massive ($\sim10^5$ M$\odot$) sub-structured stellar system in the Galactic Perseus complex likely undergoing hierarchical cluster assembly. Such a system comprises nine star clusters (including the well-known clusters NGC 654 and NGC 663) and an extended and low-density stellar halo. Gaia-DR3 and available spectroscopic data show that all its components are physically consistent in the 6D phase-space (position, parallax, and 3D motion), homogeneous in age (14 $-$ 44 Myr), and chemical content (half-solar metallicity). In addition, the system’s global stellar density distribution is that of typical star clusters and shows clear evidence of mass segregation. We find that the hierarchical structure is mostly contracting towards the center with a speed of up to $\simeq4-5$ km s$^{-1}$, while the innermost regions expand at a lower rate (about $\simeq1$ km s$^{-1}$) and are dominated by random motions. Interestingly, this pattern is dominated by the kinematics of massive stars, while low-mass stars ($M<2$ M$\odot$) are characterized by contraction across the entire cluster. Finally, the nine star clusters in the system are all characterized by a relatively flat velocity dispersion profile possibly resulting from ongoing interactions and tidal heating. We show that the observational results are generally consistent with those found in $N$-body simulations following the cluster violent relaxation phase strongly suggesting that the system is a massive cluster in the early assembly stages. This is the second structure with these properties identified in our Galaxy and, following the nomenclature of our previous work, we named it LISCA II.

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A. Croce, E. Dalessandro, A. Livernois, et. al.
Wed, 29 Mar 23
61/73

Comments: 21 pages, 24 figures, 1 table; accepted for publication in A&A

On the role of dust and mass loss in the extended main sequence turnoff of star clusters: the case of NGC 1783 [SSA]

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http://arxiv.org/abs/2303.16049


The Color Magnitude Diagram (CMD) morphology of the “extended” main sequence turnoff (eMSTO) and upper main sequence (MS) of the intermediate age ($\lesssim 2$ Gyr) Large Magellanic Cloud Cluster NGC 1783 shows the presence of a small group of UV-dim stars, that, in the ultraviolet Hubble Space Telescope filters, are located at colors on the red side of the typical “fan” shape displayed by the eMSTO. We model the UV-dim stars by assuming that some of the stars which would intrinsically be located on the left side of the eMSTO are obscured by a ring of dust due to grain condensation at the periphery of the excretion disc expelled when they spin at the high rotation rates typical of stars in the Be stage. A reasonably low optical depth at 10$\mu$ is necessary to model the UV-dim group. Introduction of dust in the interpretation of the eMSTO may require a substantial re-evaluation of previous conclusions concerning the role of age and/or rotation spreads in the MC clusters: the entire eMSTO can be populated by dusty stars, and the reddest UV-dim stars simply represents the tail of the distribution with both maximum obscuration and the dust ring seen along the line of sight. The model stars having higher rotational projected velocity ($v \sin$ i) are predicted to be preferentially redder than the slowly-rotating stars. The mass loss responsible for the dust may also cause the non-monotonic distribution of stars in the upper main sequence, with two peaks and gaps showing up in the UV CMD.

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F. D’Antona, F. Dell’Agli, M. Tailo, et. al.
Wed, 29 Mar 23
63/73

Comments: 11 pages, 13 figures. This is a pre-copyedited, author-produced PDF of an article (stad851) accepted for publication in MNRAS following peer review

Carbon-Chain Chemistry in the Interstellar Medium [GA]

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http://arxiv.org/abs/2303.15769


The presence of carbon-chain molecules in the interstellar medium (ISM) has been known since the early 1970s and $>100$ such species have been identified to date, making up $>40\%$ of the total of detected ISM molecules. They are prevalent not only in star-forming regions in our Galaxy, but also in other galaxies. These molecules provide important information on physical conditions, gas dynamics, and evolutionary stages of star-forming regions. More complex species of polycyclic aromatic hydrocarbons (PAHs) and fullerenes (C${60}$ and C${70}$) have been detected in circumstellar envelopes around carbon-rich Asymptotic Giant Branch (AGB) stars and planetary nebulae, while PAHs are also known to be a widespread component of interstellar dust in most galaxies. Recently, two line survey projects toward the starless core Taurus Molecular Cloud-1 with large single-dish telescopes have detected many new carbon-chain species, including molecules containing benzene rings. These new findings raise fresh questions about carbon-bearing species in the Universe. This article reviews various aspects of carbon-chain molecules, including observational studies, chemical simulations, quantum calculations, and laboratory experiments, and discusses open questions and how they may be answered by future facilities.

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K. Taniguchi, P. Gorai and J. Tan
Wed, 29 Mar 23
73/73

Comments: This is a review article submitted to the Publications of the Astronomical Society of Japan. Comments are welcome

On the dearth of C-enhanced metal-poor stars in the Galactic bulge [GA]

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http://arxiv.org/abs/2303.14204


The chemical fingerprints of the first stars are retained within the photospheres of ancient unevolved metal-poor stars. A significant fraction of these stellar fossils is represented by stars known as Carbon-Enhanced Metal-Poor (CEMP), $\rm [C/Fe]>+0.7$ and $\rm [Fe/H]<-2$, which are likely imprinted by low-energy primordial supernovae. These CEMP stars are largely observed in the Galactic halo and ultra-faint dwarf galaxies, with values reaching $\rm [C/Fe]=+4.5$. The Galactic bulge is predicted to host the oldest stars, but it shows a striking dearth of CEMP stars with $\rm [C/Fe]\gtrsim +2.0$. Here we explore the possible reasons for this anomaly by performing a statistical analysis of the observations of metal-poor stars in combination with the predictions of $\Lambda$CDM models. We suggest that the dearth of CEMP stars with high $\rm [C/Fe]$ is not due to the low statistics of observed metal-poor stars but is the result of the different formation process of the bulge. $N$-body simulations show that the first star-forming halos which end up in the bulge are characterized by the highest star-formation rates. These rates enable the formation of rare massive first stars exploding as pair-instability supernovae (PISNe), which wash out the signature of primordial faint supernovae. We demonstrate that the mean $\rm [C/Fe]$ of first stars polluted environments decreases with the increasing contribution of PISNe. We conclude that the dearth of CEMP stars in the Galactic bulge indirectly probes the existence of elusive PISNe, and propose a novel method which exploits this lack to constrain the mass distribution of the first stars.

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G. Pagnini, S. Salvadori, M. Rossi, et. al.
Tue, 28 Mar 23
1/81

Comments: N/A

Fishing for Planets: A Comparative Analysis of EPRV Survey Performance in the Presence of Correlated Noise [EPA]

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http://arxiv.org/abs/2303.14571


With dedicated exoplanet surveys underway for multiple extreme precision radial velocity (EPRV) instruments, the near-future prospects of RV exoplanet science are promising. These surveys’ generous time allocations are expected to facilitate the discovery of Earth analogs around bright, nearby Sun-like stars. But survey success will depend critically on the choice of observing strategy, which will determine the survey’s ability to mitigate known sources of noise and extract low-amplitude exoplanet signals. Here, we present an analysis of the Fisher information content of simulated EPRV surveys, accounting for the most recent advances in our understanding of stellar variability on both short and long timescales (i.e., oscillations and granulation within individual nights, and activity-induced variations across multiple nights). In this analysis, we capture the correlated nature of stellar variability by parameterizing these signals with Gaussian Process kernels. We describe the underlying simulation framework as well as the physical interpretation of the Fisher information content, and we evaluate the efficacy of EPRV survey strategies that have been presented in the literature. We explore and compare strategies for scheduling observations over various timescales and we make recommendations to optimize survey performance for the detection of Earth-like exoplanets.

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A. Gupta and M. Bedell
Tue, 28 Mar 23
4/81

Comments: 24 Pages, 11 Figures

A High-Eccentricity Warm Jupiter Orbiting TOI-4127 [EPA]

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http://arxiv.org/abs/2303.14570


We report the discovery of TOI-4127 b, a transiting, Jupiter-sized exoplanet on a long-period ($P = 56.39879^{+0.00010}{-0.00010}$ d), high-eccentricity orbit around a late F-type dwarf star. This warm Jupiter was first detected and identified as a promising candidate from a search for single-transit signals in TESS Sector 20 data, and later characterized as a planet following two subsequent transits (TESS Sectors 26 and 53) and follow-up ground-based RV observations with the NEID and SOPHIE spectrographs. We jointly fit the transit and RV data to constrain the physical ($R_p = 1.096^{+0.039}{-0.032} R_J$, $M_p = 2.30^{+0.11}{-0.11} M_J$) and orbital parameters of the exoplanet. Given its high orbital eccentricity ($e=0.7471^{+0.0078}{-0.0086}$), TOI-4127 b is a compelling candidate for studies of warm Jupiter populations and of hot Jupiter formation pathways. We show that the present periastron separation of TOI-4127 b is too large for high-eccentricity tidal migration to circularize its orbit, and that TOI-4127 b is unlikely to be a hot Jupiter progenitor unless it is undergoing angular momentum exchange with an undetected outer companion. Although we find no evidence for an external companion, the available observational data are insufficient to rule out the presence of a perturber that can excite eccentricity oscillations and facilitate tidal migration.

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A. Gupta, J. Jackson, G. Hebrard, et. al.
Tue, 28 Mar 23
9/81

Comments: N/A

Effective Temperature Estimations from Line Depth Ratios in the \H\ and \K-band Spectra of IGRINS [SSA]

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http://arxiv.org/abs/2303.15030


Determining accurate effective temperatures of stars buried in the dust-obscured Galactic regions is extremely difficult from photometry. Fortunately, high-resolution infrared spectroscopy is a powerful tool for determining the temperatures of stars with no dependence on interstellar extinction. It has long been known that the depth ratios of temperature-sensitive and relatively insensitive spectral lines are excellent temperature indices. In this work, we provide the first extensive line depth ratio (LDR) method application in the infrared region that encompasses both \H\ and \K\ bands (1.48 $\mu$m – 2.48 $\mu$m). We applied the LDR method to high-resolution (R $\simeq$ 45,000) \H\ and \K-band spectra of 110 stars obtained with the Immersion Grating Infrared Spectrograph (IGRINS). Our sample contained stars with 3200 $<$ \teff\ (K) $<$ 5500, 0.20 $\leq$ log g $<$ 4.6, and $-$1.5 $<$ [M/H] $<$ 0.5. Application of this method in the \K-band yielded 21 new LDR$-$\teff\ relations. We also report five new LDR$-$\teff\ relations found in the \H-band region, augmenting the relations already published by other groups. The temperatures found from our calibrations provide reliable temperatures within $\sim$70 K accuracy compared to spectral \teff\ values from the literature.

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M. Afşar, Z. Bozkurt, G. Topcu, et. al.
Tue, 28 Mar 23
13/81

Comments: 4 Tables, 8 Figures, Accepted for publication in The Astrophysical Journal

Relative efficiency of three mechanisms of vector fields growth in a random media [CL]

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http://arxiv.org/abs/2303.14388


We consider a model of a random media with fixed and finite memory time with abrupt losses of memory (renovation model). Within the memory intervals we can observe either amplification or oscillation of the vector field in a given particle. The cumulative effect of amplifications in many subsequent intervals leads to amplification of the mean field and mean energy. Similarly, the cumulative effect of intermittent amplifications or oscillations also leads to amplification of the mean field and mean energy, however, at a lower rate. Finally, the random oscillations alone can resonate and yield the growth of the mean field and energy. These are the three mechanisms that we investigate and compute analytically and numerically the growth rates based on the Jacobi equation with the random curvature parameter.

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E. Illarionov and D. Sokoloff
Tue, 28 Mar 23
14/81

Comments: N/A

Ultracool dwarfs candidates based on six years of the Dark Energy Survey data [SSA]

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http://arxiv.org/abs/2303.15156


We present a sample of 19,583 ultracool dwarf candidates brighter than z $\leq 23$ selected from the Dark Energy Survey DR2 coadd data matched to VHS DR6, VIKING DR5 and AllWISE covering $\sim$ 4,800 $deg^2$. The ultracool candidates were first pre-selected based on their (i-z), (z-Y), and (Y-J) colours. They were further classified using a method that compares their optical, near-infrared and mid-infrared colours against templates of M, L and T dwarfs. 14,099 objects are presented as new L and T candidates and the remaining objects are from the literature, including 5,342 candidates from our previous work. Using this new and deeper sample of ultracool dwarf candidates we also present: 20 new candidate members to nearby young moving groups (YMG) and associations, variable candidate sources and four new wide binary systems composed of two ultracool dwarfs. Finally, we also show the spectra of twelve new ultracool dwarfs discovered by our group and presented here for the first time. These spectroscopically confirmed objects are a sanity check of our selection of ultracool dwarfs and photometric classification method.

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M. Ponte, B. Santiago, A. Rosell, et. al.
Tue, 28 Mar 23
18/81

Comments: 18 pages, 10 figures, 7 tables. Accepted for publication in MNRAS

TIC 219006972: A Compact, Coplanar Quadruple Star System Consisting of Two Eclipsing Binaries with an Outer Period of 168 days [SSA]

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http://arxiv.org/abs/2303.14275


We present the discovery of a new highly compact quadruple star system, TIC 219006972, consisting of two eclipsing binary stars with orbital periods of 8.3 days and 13.7 days, and an outer orbital period of only 168 days. This period is a full factor of 2 shorter than the quadruple with the shortest outer period reported previously, VW LMi, where the two binary components orbit each other every 355 days. The target was observed by TESS in Full-Frame Images in sectors 14-16, 21-23, 41, 48 and 49, and produced two sets of primary and secondary eclipses. These show strongly non-linear eclipse timing variations (ETVs) with an amplitude of $\sim$0.1 days, where the ETVs of the primary and secondary eclipses, and of the two binaries are all largely positively correlated. This highlights the strong dynamical interactions between the two binaries and confirms the compact quadruple configuration of TIC 219006972. The two eclipsing binaries are nearly circular whereas the quadruple system has an outer eccentricity of about 0.25. The entire system is nearly edge-on, with a mutual orbital inclination between the two eclipsing binary star systems of about 1 degree.

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V. Kostov, T. Borkovits, S. Rappaport, et. al.
Tue, 28 Mar 23
23/81

Comments: 16 pages, 13 figures, 4 tables, MNRAS accepted

Towards robust corrections for stellar contamination in JWST exoplanet transmission spectra [EPA]

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http://arxiv.org/abs/2303.15418


Transmission spectroscopy is still the preferred characterization technique for exoplanet atmospheres, although it presents unique challenges which translate into characterization bottlenecks when robust mitigation strategies are missing. Stellar contamination is one of such challenges that can overpower the planetary signal by up to an order of magnitude, and thus not accounting for stellar contamination can lead to significant biases in the derived atmospheric properties. Yet, accounting for stellar contamination may not be straightforward, as important discrepancies exist between state-of-the-art stellar models and measured spectra and between models themselves. Here we explore the extent to which stellar models can be used to reliably correct for stellar contamination and yield a planet’s uncontaminated transmission spectrum. We find that (1) discrepancies between stellar models can dominate the noise budget of JWST transmission spectra of planets around stars with heterogeneous photospheres; (2) the true number of unique photospheric spectral components and their properties can only be accurately retrieved when the stellar models have a sufficient fidelity; and (3) under such optimistic circumstances the contribution of stellar contamination to the noise budget of a transmission spectrum is considerably below that of the photon noise for the standard transit observation setup. Therefore, we suggest (1) increased efforts towards development of model spectra of stars and their active regions in a data-driven manner; and (2) the development of empirical approaches for deriving spectra of photospheric components using the observatories with which the atmospheric explorations are carried out.

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B. Rackham and J. Wit
Tue, 28 Mar 23
24/81

Comments: 15 pages, 8 figures, 2 tables

Imaging Molecular Outflow in Massive Star-forming Regions with HNCO Lines [GA]

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http://arxiv.org/abs/2303.14866


Protostellar outflows are considered a signpost of star formation. These outflows can cause shocks in the molecular gas and are typically traced by the line wings of certain molecules. HNCO (4–3) has been regarded as a shock tracer because of the high abundance in shocked regions. Here we present the first imaging results of HNCO (4–3) line wings toward nine sources in a sample of twenty three massive star-forming regions using the IRAM 30\,m telescope. We adopt the velocity range of the full width of HC$_{3}$N (10–9) and H$^{13}$CO$^+$ (1–0) emissions as the central emission values, beyond which the emission from HNCO (4–3) is considered to be from line wings. The spatial distributions of the red- and/or blue-lobes of HNCO (4–3) emission nicely associate with those lobes of HCO$^{+}$ (1–0) in most of the sources. High intensity ratios of HNCO (4–3) to HCO$^+$ (1–0) are obtained in the line wings. The derived column density ratios of HNCO to HCO$^+$ are consistent with those previously observed towards massive star-forming regions. These results provide direct evidence that HNCO could trace outflow in massive star-forming regions. This work also implies that the formation of some HNCO molecules is related to shock, either on the grain surface or within the shocked gas.

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J. Xie, J. Li, J. Wang, et. al.
Tue, 28 Mar 23
31/81

Comments: 18 pages, 4 tables, 4 figures, and accepted for publication in ApJ

A new value of the period of the classical Cepheid RT Aur on the basis of 456 times of maximum, 1897-2023 [SSA]

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http://arxiv.org/abs/2303.14781


The present study collects 456 new times of maximum light of the classical Cepheid RT Aur, covering the period from 1897 to 2022. The O-C diagram resulting from these observations shows that the period given by the GCVS has to be corrected. It results that no strong period variation is found. However, the observed O-C residuals show a long term periodic trend. In the hypothesis of RT Aur being in a binary system, an orbit cannot be deduced from the available astrophysical data.

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G. Boistel
Tue, 28 Mar 23
38/81

Comments: 8 pages; 6 figures ; links to download data on GEOS website

The GAPS Programme at TNG XLII. A characterisation study of the multi-planet system around the 400 Myr-old star HD 63433 (TOI-1726) [EPA]

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http://arxiv.org/abs/2303.15242


For more than two years, we monitored with the HARPS-N spectrograph the 400 Myr-old star HD\,63433, which hosts two close-in (orbital periods $P_b\sim7.1$ and $P_c\sim20.5$ days) sub-Neptunes detected by the TESS space telescope, and it was announced in 2020. Using radial velocities and additional TESS photometry, we aim to provide the first measurement of their masses, improve the measure of their size and orbital parameters, and study the evolution of the atmospheric mass-loss rate due to photoevaporation. We tested state-of-the-art analysis techniques and different models to mitigate the dominant signals due to stellar activity that are detected in the radial velocity time series. We used a hydro-based analytical description of the atmospheric mass-loss rate, coupled with a core-envelope model and stellar evolutionary tracks, to study the past and future evolution of the planetary masses and radii. We derived new measurements of the planetary orbital periods and radii ($P_b=7.10794\pm0.000009$ d, $r_b=2.02^{+0.06}{-0.05}$ $R{\oplus}$; $P_c=20.54379\pm0.00002$ d, $r_c=2.44\pm0.07$ $R_{\oplus}$), and determined mass upper limits ($m_b\lesssim$11 $M_{\oplus}$; $m_c\lesssim$31 $M_{\oplus}$; 95$\%$ confidence level), with evidence at a 2.1–2.7$\sigma$ significance level that HD\,63433\,c might be a dense mini-Neptune with a Neptune-like mass. For a grid of test masses below our derived dynamical upper limits, we found that HD\,63433\,b has very likely lost any gaseous H-He envelope, supporting HST-based observations that are indicative of there being no ongoing atmospheric evaporation. HD\,63433\,c will keep evaporating over the next $\sim$5 Gyr if its current mass is $m_c\lesssim$15 $M_{\oplus}$, while it should be hydrodynamically stable for higher masses.

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M. Damasso, D. Locci, S. Benatti, et. al.
Tue, 28 Mar 23
42/81

Comments: 22 pages, accepted for publication on Astronomy & Astrophysics

Science opportunities with solar sailing smallsats [EPA]

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http://arxiv.org/abs/2303.14917


Recently, we witnessed how the synergy of small satellite technology and solar sailing propulsion enables new missions. Together, small satellites with lightweight instruments and solar sails offer affordable access to deep regions of the solar system, also making it possible to realize hard-to-reach trajectories that are not constrained to the ecliptic plane. Combining these two technologies can drastically reduce travel times within the solar system, while delivering robust science. With solar sailing propulsion capable of reaching the velocities of ~5-10 AU/yr, missions using a rideshare launch may reach the Jovian system in two years, Saturn in three. The same technologies could allow reaching solar polar orbits in less than two years. Fast, cost-effective, and maneuverable sailcraft that may travel outside the ecliptic plane open new opportunities for affordable solar system exploration, with great promise for heliophysics, planetary science, and astrophysics. Such missions could be modularized to reach different destinations with different sets of instruments. Benefiting from this progress, we present the “Sundiver” concept, offering novel possibilities for the science community. We discuss some of the key technologies, the current design of the Sundiver sailcraft vehicle and innovative instruments, along with unique science opportunities that these technologies enable, especially as this exploration paradigm evolves. We formulate policy recommendations to allow national space agencies, industry, and other stakeholders to establish a strong scientific, programmatic, and commercial focus, enrich and deepen the space enterprise and broaden its advocacy base by including the Sundiver paradigm as a part of broader space exploration efforts.

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S. Turyshev, D. Garber, L. Friedman, et. al.
Tue, 28 Mar 23
43/81

Comments: 34 pages, 12 figures, 2 tables

Automated Speckle Interferometry of Known Binaries [IMA]

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http://arxiv.org/abs/2303.15011


Astronomers have been measuring the separations and position angles between the two components of binary stars since William Herschel began his observations in 1781. In 1970, Anton Labeyrie pioneered a method, speckle interferometry, that overcomes the usual resolution limits induced by atmospheric turbulence by taking hundreds or thousands of short exposures and reducing them in Fourier space. Our 2022 automation of speckle interferometry allowed us to use a fully robotic 1.0-meter PlaneWave Instruments telescope, located at the El Sauce Observatory in the Atacama Desert of Chile, to obtain observations of many known binaries with established orbits. The long-term objective of these observations is to establish the precision, accuracy, and limitations of this telescope’s automated speckle interferometry measurements. This paper provides an early overview of the Known Binaries Project and provide example results on a small-separation (0.27″) binary, WDS 12274-2843 B 228.

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N. Hardy, L. Bewersdorff, D. Rowe, et. al.
Tue, 28 Mar 23
45/81

Comments: N/A

Fundamental effective temperature measurements for eclipsing binary stars — IV. Selection of new benchmark stars and first results for HD 22064 [SSA]

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http://arxiv.org/abs/2303.15008


I describe the selection and initial characterisation of 20 eclipsing binary stars that are suitable for calibration and testing of stellar models and data analysis algorithms used by the PLATO mission and spectroscopic surveys. The binary stars selected are F-/G-type dwarf stars with M-type dwarf companions that contribute less than 2% of the flux at optical wavelengths. The light curves typically show well-defined total eclipses with very little variability between the eclipses. I have used near-infrared spectra obtained by the APOGEE survey to measure the spectroscopic orbit for both stars in HD22064. Combined with an analysis of the TESS light curve, I derive the following masses and radii: $M_1 = 1.35 \pm 0.03 M_{\odot}$, $M_2 = 0.58 \pm 0.01 M_{\odot}$, $R_1 = 1.554 \pm 0.014 R_{\odot}$, $R_2 = 0.595 \pm 0.008 R_{\odot}$. Using $R_1$ and the parallax from Gaia EDR3, I find that the primary star’s angular diameter is $\theta = 0.1035 \pm 0.0009 $ mas. The apparent bolometric flux of the primary star is ${\mathcal F}{\oplus,0} = (7.51\pm 0.09)\times10^{-9}$ erg cm$^{-2}$ s$^{-1}$. Hence, this F2V star has an effective temperature $T{\rm eff,1} = 6763{\rm\,K} \pm 39{\rm \,K}$. HD22064 is an ideal benchmark star that can be used for “end-to-end” tests of the stellar parameters measured by large-scale spectroscopic surveys, or stellar parameters derived from asteroseismology with PLATO. The techniques described here for HD22064 can be applied to the other eclipsing binaries in the sample in order to create an all-sky network of such benchmark stars.

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P. Maxted
Tue, 28 Mar 23
52/81

Comments: 12 pages, 9 figures. Submitted to MNRAS. arXiv admin note: text overlap with arXiv:2205.01466

Photometric Observations and Period Analysis of an SU UMa-type Dwarf Nova, MASTER OT J004527.52+503213.8 [SSA]

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http://arxiv.org/abs/2303.14558


MASTER OT J004527.52+503213.8 (hereafter MASTER J004527) is a dwarf nova discovered by the MASTER project in 2013. At 18:20 UTC on 24 October 2020, brightening of this object was reported to vsnet-alert (24843 by Denisenko). This was the second report of a superoutburst after its discovery. Photometric observations were made using the 23.5-cm Schmidt-Cassegrain telescope at Okayama University of Science observatory soon after the alert through 4 November 2020. In this work, we present the photometric data from our observation, and the analysis of the light curves of MASTER J004527 during the 2020 outburst. We propose a method to determine the period of superhumps by polynomial fitting, which can be applied to a light curve with many missing data. In addition to our own data, we incorporate other all sky survey data of the outburst to better understand the properties of the superhumps. Based on our observations, we conclude that MASTER J004527 is an SU UMa-type dwarf nova, since no early superhumps occurred.

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S. Matsui, T. Takeuchi, K. Kono, et. al.
Tue, 28 Mar 23
53/81

Comments: Accepted for publication in JAAVSO, 9 pages, 8 figures

The astrophysical $S-$factor and reaction rate for $^{15}$N($p,γ$)$^{16}$O within the modified potential cluster model [CL]

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http://arxiv.org/abs/2303.14680


We study a radiative $p^{15}$N capture on the ground state of $^{16}$O at stellar energies within the framework of a modified potential cluster model (MPCM) with forbidden states, including low lying resonances. The investigation of the $^{15}$N($p,\gamma $)$^{16}$O reaction includes the consideration of $^{3}S_{1}$ resonances due to $E1$ transitions and contribution of $^{3}P_{1}$ scattering wave in $p$ + $^{15}$N channel due to $^{3}P_{1}\longrightarrow $ $^{3}P_{0}$ $M1$ transition. We calculate the astrophysical low-energy $S-$factor and extrapolated $S(0)$ turned out to be within $34.7-40.4$ keV$\cdot $b. It is elucidated the important role of the asymptotic constant (AC) for the $^{15}$N($p,\gamma $)$^{16}$O process with interfering $^{3}S_{1}$(312) and $^{3}S_{1}$(962) resonances. A comparison of our calculation for $S-$factor with existing experimental and theoretical data is addressed and the reasonable agreement is found.
The reaction rate is calculated and compared with the existing rates. It has negligible dependence on the variation of AC, but shows strong impact of the interference of $^{3}S_{1}$(312) and $^{3}S_{1}$(962) resonances, especially at $T_{9}$ referring to the CNO Gamow windows. We present a stellar temperature dependence on the Gamow energy and a comparison of rates for radiative proton capture reactions for CNO cycle on nitrogen isotopes obtained in the framework of the MPCM and give temperature windows, prevalence, and significance of each process.

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S. Dubovichenko, N. Burkova, R. Kezerashvili, et. al.
Tue, 28 Mar 23
55/81

Comments: 15 pages, 8 figures

First observational evidence of a relation between globular clusters' internal rotation and stellar masses [GA]

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http://arxiv.org/abs/2303.15253


Several observational studies have shown that many Galactic globular clusters (GCs) are characterised by internal rotation. Theoretical studies of the dynamical evolution of rotating clusters have predicted that, during their long-term evolution, these stellar systems should develop a dependence of the rotational velocity around the cluster’s centre on the mass of stars, with the internal rotation increasing for more massive stars. In this paper we present the first observational evidence of the predicted rotation-mass trend. In our investigation, we exploited the $\mathit{Gaia}$ Data Release 3 catalogue of three GCs: NGC 104 (47 Tuc), NGC 5139 ($\omega$ Cen) and NGC 5904 (M 5). We found clear evidence of a cluster rotation-mass relation in 47 Tuc and M 5, while in $\omega$ Cen, the dynamically youngest system among the three clusters studied here, no such trend was detected.

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M. Scalco, A. Livernois, E. Vesperini, et. al.
Tue, 28 Mar 23
57/81

Comments: 6 pages, 4 figures, 1 table. Accepted for publication in MNRAS Letters

Numerical simulations of prominence oscillations triggered by external perturbations [SSA]

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http://arxiv.org/abs/2303.15348


Several energetic disturbances have been identified as triggers of the large-amplitude oscillations (LAOs) in prominences. However, the mechanisms for LAOs excitation are not well understood. We aim to study these mechanisms, performing time-dependent numerical simulations in 2.5D and 2D setups using magnetohydrodynamic (MHD) code MANCHA3D. Two types of disturbances are applied to excite prominence oscillations, such as a perturbation associated with an eruption and the waves caused by an artificial energy release. In the simulation with the eruption, we obtain that it does not produce LAOs in the prominence located in its vicinity. While the erupting flux rope rises, an elongated current sheet forms behind it, which becomes unstable and breaks into plasmoids. The downward-moving plasmoids cause perturbations in the velocity field by merging with the post-reconnection loops. This velocity perturbation propagates in the surroundings and perturbs the nearby prominence. The analysis of the oscillatory motions of the prominence plasma reveals the excitation of small-amplitude oscillations (SAOs), which are a mixture of longitudinal and vertical oscillations. In the simulation with a distant artificial perturbation, a fast-mode shock wave is produced, and it gradually reaches two flux rope prominences at different distances. This shock wave excites vertical LAOs and longitudinal SAOs with similar amplitudes, periods, and damping times in both prominences. Finally, in the experiment with the external triggering of LAOs in a dipped arcade prominence model, we find that, although the vector normal to the front of a fast-mode shock wave is parallel to the spine of the dipped arcade well before the contact, this wave does not excite longitudinal LAOs. When the wave front approaches the prominence, it pushes the dense plasma down, establishing vertical LAOs.

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V. Liakh, M. Luna and E. Khomenko
Tue, 28 Mar 23
58/81

Comments: 18 pages, 18 figures, accepted for publication in Astronomy and Astrophysics

HelioCast: heliospheric forecasting based on white-light observations of the solar corona. I. Solar minimum conditions [SSA]

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http://arxiv.org/abs/2303.14972


We present a new 3D MHD heliospheric model for space-weather forecasting driven by boundary conditions defined from white-light observations of the solar corona. The model is based on the MHD code PLUTO, constrained by an empirical derivation of the solar wind background properties at 0.1au. This empirical method uses white-light observations to estimate the position of the heliospheric current sheet. The boundary conditions necessary to run HelioCast are then defined from pre-defined relations between the necessary MHD properties (speed, density and temperature) and the distance to the current sheet. We assess the accuracy of the model over six Carrington rotations during the first semester of 2018. Using point-by-point metrics and event based analysis, we evaluate the performances of our model varying the angular width of the slow solar wind layer surrounding the heliospheric current sheet. We also compare our empirical technique with two well tested models of the corona: Multi-VP and WindPredict-AW. We find that our method is well suited to reproduce high speed streams, and does — for well chosen parameters — better than full MHD models. The model shows, nonetheless, limitations that could worsen for rising and maximum solar activity.

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V. Réville, N. Poirier, A. Kouloumvakos, et. al.
Tue, 28 Mar 23
64/81

Comments: Accepted for publication in the Journal of Space Weather and Space Climate. 23 pages, 12 figures. The model runs live at this http URL

Are magnetic fields universal in O-type multiple systems? [SSA]

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http://arxiv.org/abs/2303.14791


Although significant progress has been achieved in recent surveys of the magnetism in massive stars, the origin of the detected magnetic fields remains to be the least understood topic in their studies. We present an analysis of 61 high-resolution spectropolarimetric observations of 36 systems with O-type primaries, among them ten known particle-accelerating colliding-wind binaries exhibiting synchrotron radio emission. Our sample consists of multiple systems with components at different evolutionary stages with wide and tight orbits and different types of interactions. For the treatment of the complex composite spectra of the multiple systems, we used a special procedure involving different line masks populated for each element separately. Out of the 36 systems, 22 exhibit in their LSD Stokes V profiles definitely detected Zeeman features, among them seven systems with colliding winds. For fourteen systems the detected Zeeman features are most likely associated with O-type components whereas for three systems we suggest an association with an early B-type component. For the remaining five systems the source of the field is unclear. Marginal evidence for the detection of a Zeeman feature is reported for eleven systems and non-detection for three systems. The large number of systems with definitely detected Zeeman features presents a mystery, but probably indicates that multiplicity plays a definite role in the generation of magnetic fields in massive stars. The newly found magnetic systems are supreme candidates for spectropolarimetric monitoring over their orbital and rotation periods to obtain trustworthy statistics on the magnetic field geometry and the distribution of field strength.

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S. Hubrig, S. Jarvinen, I. Ilyin, et. al.
Tue, 28 Mar 23
66/81

Comments: 21 pages, 2 tables, 9 figures, accepted for publication in MNRAS

The Shapes of Stellar Spectra [SSA]

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http://arxiv.org/abs/2303.14340


Stellar atmospheres separate the hot and dense stellar interiors from the emptiness of space. Radiation escapes from the outermost layers of a star, carrying direct physical information. Underneath the atmosphere, the very high opacity keeps radiation thermalized and resembling a black body with the local temperature. In the atmosphere the opacity drops, and radiative energy leaks out, which is redistributed in wavelength according to the physical processes by which matter and radiation interact, in particular photoionization. In this article, I will evaluate the role of photoionization in shaping the stellar energy distribution of stars. To that end, I employ simple, state-of-the-art plane-parallel model atmospheres and a spectral synthesis code, dissecting the effects of photoionization from different chemical elements and species, for stars of different masses in the range of 0.3 to 2 M$_{\odot}$. I examine and interpret the changes in the observed spectral energy distributions of the stars as a function of the atmospheric parameters. The photoionization of atomic hydrogen and H$^-$ are the most relevant contributors to the continuum opacity in the optical and near-infrared regions, while heavier elements become important in the ultraviolet region. In the spectra of the coolest stars (spectral types M and later), the continuum shape from photoionization is no longer recognizable due to the accumulation of lines, mainly from molecules. These facts have been known for a long time, but the calculations presented provide an updated quantitative evaluation and insight into the role of photoionization on the structure of stellar atmospheres.

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C. Prieto
Tue, 28 Mar 23
69/81

Comments: Accepted and published by Atoms. Part of the special issue on Photoionization of Atoms, edited by S. Nahar and G. Hinojosa

Predicting light curves of RR Lyrae variables using artificial neural network based interpolation of a grid of pulsation models [SSA]

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http://arxiv.org/abs/2303.15117


We present a new technique to generate the light curves of RRab stars in different photometric bands ($I$ and $V$ bands) using Artificial Neural Networks (ANN). A pre-computed grid of models was used to train the ANN, and the architecture was tuned using the $I$ band light curves. The best-performing network was adopted to make the final interpolators in the $I$ and $V$ bands. The trained interpolators were used to predict the light curve of RRab stars in the Magellanic Clouds, and the distances to the LMC and SMC were determined based on the reddening independent Wesenheit index. The estimated distances are in good agreement with the literature. The comparison of the predicted and observed amplitudes, and Fourier amplitude ratios showed good agreement, but the Fourier phase parameters displayed a few discrepancies. To showcase the utility of the interpolators, the light curve of the RRab star EZ Cnc was generated and compared with the observed light curve from the Kepler mission. The reported distance to EZ Cnc was found to be in excellent agreement with the updated parallax measurement from Gaia EDR3. Our ANN interpolator provides a fast and efficient technique to generate a smooth grid of model light curves for a wide range of physical parameters, which is computationally expensive and time-consuming using stellar pulsation codes.

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N. Kumar, A. Bhardwaj, H. Singh, et. al.
Tue, 28 Mar 23
75/81

Comments: Accepted for publication in MNRAS

Gravitational polarization of test-mass potential in equilibrium polytropic sheets with non-negative polytropic indexes [GA]

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http://arxiv.org/abs/2303.14876


Gravitational polarization is examined for equilibrium self-gravitating polytropic sheets perturbed by gravitational field due to test mass sheet. We find equilibrium solutions to the corresponding perturbed Lane-Emden equations for non-negative polytropic indexes. It is shown that gravitational polarization may be observed even in a finite extent of self-gravitating systems in addition to previously discussed infinite systems. In the polytropic sheets, the maximum gravitational amplification gets greater with a higher polytropic index while the height at which the maximum amplification occurs gets lower. The ratio of height change to the original height increases with polytropic index. The last result constrains the linear approximation method used for the present perturbation method.

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Y. Ito
Tue, 28 Mar 23
78/81

Comments: N/A

Orbital decay in an accreting and eclipsing 13.7 minute orbital period binary with a luminous donor [SSA]

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http://arxiv.org/abs/2303.13573


We report the discovery of ZTF J0127+5258, a compact mass-transferring binary with an orbital period of 13.7 minutes. The system contains a white dwarf accretor, which likely originated as a post-common envelope carbon-oxygen (CO) white dwarf, and a warm donor ($T_{\rm eff,\,donor}= 16,400\pm1000\,\rm K$). The donor probably formed during a common envelope phase between the CO white dwarf and an evolving giant which left behind a helium star or helium white dwarf in a close orbit with the CO white dwarf. We measure gravitational wave-driven orbital inspiral with $\sim 35\sigma$ significance, which yields a joint constraint on the component masses and mass transfer rate. While the accretion disk in the system is dominated by ionized helium emission, the donor exhibits a mixture of hydrogen and helium absorption lines. Phase-resolved spectroscopy yields a donor radial-velocity semi-amplitude of $771\pm27\,\rm km\, s^{-1}$, and high-speed photometry reveals that the system is eclipsing. We detect a {\it Chandra} X-ray counterpart with $L_{X}\sim 3\times 10^{31}\,\rm erg\,s^{-1}$. Depending on the mass-transfer rate, the system will likely evolve into either a stably mass-transferring helium CV, merge to become an R Crb star, or explode as a Type Ia supernova in the next million years. We predict that the Laser Space Interferometer Antenna (LISA) will detect the source with a signal-to-noise ratio of $24\pm6$ after 4 years of observations. The system is the first \emph{LISA}-loud mass-transferring binary with an intrinsically luminous donor, a class of sources that provide the opportunity to leverage the synergy between optical and infrared time domain surveys, X-ray facilities, and gravitational-wave observatories to probe general relativity, accretion physics, and binary evolution.

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K. Burdge, K. El-Badry, S. Rappaport, et. al.
Mon, 27 Mar 23
5/59

Comments: 13 pages, 7 figures, 2 tables, submitted to ApJL

New Resonances of Supernova Neutrinos in Twisting Magnetic Fields [CL]

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http://arxiv.org/abs/2303.13572


We investigate the effect of resonant spin conversion of the neutrinos induced by the geometrical phase in a twisting magnetic field. We find that the geometrical phase originating from the rotation of the transverse magnetic field along the neutrino trajectory can trigger a new resonant spin conversion of Dirac neutrinos inside the supernova, even if there were no such transitions in the fixed-direction field case. We have shown that even though resonant spin conversion is too weak to affect solar neutrinos, it could have a remarkable consequence on supernova neutronization bursts where very intense magnetic fields are quite likely. We demonstrate how the flavor composition at Earth can be used as a probe to establish the presence of non-negligible magnetic moments, potentially down to $10^{-15}~\mu_B$ in upcoming neutrino experiments like the Deep Underground Neutrino Experiment (DUNE), and the Hyper-Kamiokande (HK). Possible implications are analyzed.

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S. Jana and Y. Porto
Mon, 27 Mar 23
7/59

Comments: 5 pages + references, 3 figures

Unveiling the mechanism for the rapid acceleration phase in a solar eruption [SSA]

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http://arxiv.org/abs/2303.14050


Two major mechanisms have been proposed to drive the solar eruptions: the ideal magnetohydrodynamic instability and the resistive magnetic reconnection. Due to the close coupling and synchronicity of the two mechanisms, it is difficult to identify their respective contribution to solar eruptions, especially to the critical rapid acceleration phase. Here, to shed light on this problem, we conduct a data-driven numerical simulation for the flux rope eruption on 2011 August 4, and quantify the contributions of the upward exhaust of the magnetic reconnection along the flaring current sheet and the work done by the large-scale Lorentz force acting on the flux rope. Major simulation results of the eruption, such as the macroscopic morphology, early kinematics of the flux rope and flare ribbons, match well with the observations. We estimate the energy converted from the magnetic slingshot above the current sheet and the large-scale Lorentz force exerting on the flux rope during the rapid acceleration phase, and find that (1) the work done by the large-scale Lorentz force is about 4.6 times higher than the former, and (2) decreased strapping force generated by the overlying field facilitates the eruption. These results indicate that the large-scale Lorentz force plays a dominant role in the rapid acceleration phase for this eruption.

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Z. Zhong, Y. Guo, T. Wiegelmann, et. al.
Mon, 27 Mar 23
8/59

Comments: 12 pages, 5 figures; Accepted for publication in ApJL

Analytic understanding of the resonant nature of Kozai Lidov Cycles with a precessing quadruple potential [HEAP]

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http://arxiv.org/abs/2303.13579


The very long-term evolution of the hierarchical restricted three-body problem with a precessing quadruple potential is studied analytically. This problem describes the evolution of a star and a planet which are perturbed either by a (circular and not too inclined) binary star system or by one other star and a second more distant star, as well as a perturbation by one distant star and the host galaxy or a compact-object binary system orbiting a massive black hole in non-spherical nuclear star clusters \citep{arXiv:1705.02334v2, arXiv:1705.05848v2}. Previous numerical experiments have shown that when the precession frequency is comparable to the Kozai-Lidov time scale, long term evolution emerges that involves extremely high eccentricities with potential applications for a broad scope of astrophysical phenomena including systems with merging black holes, neutron stars or white dwarfs. We show that a central ingredient of the dynamics is a resonance between the perturbation frequency and the precession frequency of the eccentricity vector in the regime where the eccentricity vector, the precession axis and the quadruple direction are closely aligned. By averaging the secular equations of motion over the Kozai-Lidov Cycles we solve the problem analytically in this regime.

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Y. Klein and B. Katz
Mon, 27 Mar 23
9/59

Comments: 5 pages, 2 figures

Designing wavelength sampling for Fabry-Pérot observations. Information-based spectral sampling [SSA]

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http://arxiv.org/abs/2303.13875


Fabry-P\’erot interferometers (FPIs) have become very popular in solar observations because they offer a balance between cadence, spatial resolution, and spectral resolution through a careful design of the spectral sampling scheme according to the observational requirements of a given target. However, an efficient balance requires knowledge of the expected target conditions, the properties of the chosen spectral line, and the instrumental characteristics. Our aim is to find a method that allows finding the optimal spectral sampling of FPI observations in a given spectral region. In this study, we propose a technique based on a sequential selection approach where a neural network is used to predict the spectrum (or physical quantities, if the model is known) from the information at a few points. Only those points that contain relevant information and improve the model prediction are included in the sampling scheme. The method adapts the separation of the points according to the spectral resolution of the instrument, the typical broadening of the spectral shape, and the typical Doppler velocities. The experiments using the CaII 8542 A line show that the resulting wavelength scheme naturally places more points in the core than in the wings, consistent with the sensitivity of the spectral line at each wavelength interval. The method can also be used as an accurate interpolator, to improve the inference of the magnetic field when using the weak-field approximation. Overall, this method offers an objective approach for designing new instrumentation or observing proposals with customized configurations for specific targets. This is particularly relevant when studying highly dynamic events in the solar atmosphere with a cadence that preserves spectral coherence without sacrificing much information.

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C. Baso, L. Voort, J. Rodríguez, et. al.
Mon, 27 Mar 23
10/59

Comments: 8 pages, 7 figures, accepted for publication in A&A

The GALAH survey: New diffuse interstellar bands found in residuals of 872,000 stellar spectra [GA]

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http://arxiv.org/abs/2303.14016


We use more than 872,000 mid-to-high resolution (R $\sim$ 20,000) spectra of stars from the GALAH survey to discern the spectra of diffuse interstellar bands (DIBs). We use four windows with the wavelength range from 4718 to 4903, 5649 to 5873, 6481 to 6739, and 7590 to 7890 \AA, giving a total coverage of 967 \AA. We produce $\sim$400,000 spectra of interstellar medium (ISM) absorption features and correct them for radial velocities of the DIB clouds. Ultimately, we combine the 33,115 best ISM spectra into six reddening bins with a range of $0.1 \,\mathrm{mag} < E\mathrm{(B-V)} < 0.7\, \mathrm{mag}$. A total of 183 absorption features in these spectra qualify as DIBs, their fitted model parameters are summarized in a detailed catalogue. From these, 64 are not reported in the literature, among these 17 are certain, 14 are probable and 33 are possible. We find that the broad DIBs can be fitted with a multitude of narrower DIBs. Finally, we create a synthetic DIB spectrum at unit reddening which should allow us to narrow down the possible carriers of DIBs and explore the composition of the ISM and ultimately better model dust and star formation as well as to correct Galactic and extragalactic observations. The majority of certain DIBs show a significant excess of equivalent width when compared to reddening. We explain this with observed lines of sight penetrating more uniform DIB clouds compared to clumpy dust clouds.

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R. Vogrinčič, J. Kos, T. Zwitter, et. al.
Mon, 27 Mar 23
16/59

Comments: 28 pages, 15 figures, 11 tables, accepted for publication in MNRAS

Thermodynamic and Magnetic Topology Evolution of the X1.0 Flare on 2021 October 28 Simulated by a Data-driven Radiative Magnetohydrodynamic Model [SSA]

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http://arxiv.org/abs/2303.13980


Solar filament eruptions, flares and coronal mass ejections (CMEs) are manifestations of drastic release of energy in the magnetic field, which are related to many eruptive phenomena from the Earth magnetosphere to black hole accretion disks. With the availability of high-resolution magnetograms on the solar surface, observational data-based modelling is a promising way to quantitatively study the underlying physical mechanisms behind observations. By incorporating thermal conduction and radiation losses in the energy equation, we develop a new data-driven radiative magnetohydrodynamic (MHD) model, which has the capability to capture the thermodynamic evolution compared to our previous zero-\b{eta} model. Our numerical results reproduce major observational characteristics of the X1.0 flare on 2021 October 28 in NOAA active region (AR) 12887, including the morphology of the eruption, kinematic of flare ribbons, extreme-ultraviolet (EUV) radiations, and two components of the EUV waves predicted by the magnetic stretching model, i.e., a fast-mode shock wave and a slower apparent wave due to successive stretching of magnetic field lines. Moreover, some intriguing phenomena are revealed in the simulation. We find that flare ribbons separate initially and ultimately stop at the outer stationary quasi-separatrix layers (QSLs). Such outer QSLs correspond to the border of the filament channel and determine the final positions of flare ribbons, which can be used to predict the size and the lifetime of a flare before it occurs. In addition, the side view of the synthesized EUV and white-light images exhibit typical three-part structures of CMEs, where the bright leading front is roughly cospatial with the non-wave component of the EUV wave, reinforcing the magnetic stretching model for the slow component of EUV waves.

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J. Guo, Y. Ni, Z. Zhong, et. al.
Mon, 27 Mar 23
17/59

Comments: 46 pages, 15 figures, accepted for publication in The Astrophysical Journal Supplement

Minuscule corrections to near-surface solar internal rotation using mode-coupling [SSA]

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http://arxiv.org/abs/2303.13699


The observed solar oscillation spectrum is influenced by internal perturbations such as flows and structural asphericities. These features induce splitting of characteristic frequencies and distort the resonant-mode eigenfunctions. Global axisymmertric flow — differential rotation — is a very prominent perturbation. Tightly constrained rotation profiles as a function of latitude and radius are products of established helioseismic pipelines that use observed Dopplergrams to generate frequency-splitting measurements at high precision. However, the inference of rotation using frequency-splittings do not consider the effect of mode-coupling. This approximation worsens for high-angular-degree modes, as they become increasingly proximal in frequency. Since modes with high angular degrees probe the near-surface layers of the Sun, inversions considering coupled modes could potentially lead to more accurate estimates of rotation very close to the surface. In order to investigate if this is indeed the case, we perform inversions for solar differential rotation, considering coupling of modes for angular degrees $160 \leq \ell \leq 300$ in the surface gravity $f$-branch and first-overtone $p$ modes. In keeping with the character of mode coupling, we carry out a non-linear inversion using an eigenvalue solver. Differences in inverted profiles for frequency splitting measurements from MDI and HMI are compared and discussed. We find that corrections to the near-surface differential rotation profile, when accounting for mode-coupling effects, are smaller than 0.003 nHz and hence are insignificant. These minuscule corrections are found to be correlated with the solar cycle. We also present corrections to even-order splitting coefficients, which could consequently impact inversions for structure and magnetic fields.

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S. Das, S. Kashyap, D. Oktay, et. al.
Mon, 27 Mar 23
18/59

Comments: 21 pages; 15 figures; Accepted for publication in the Astrophysical Journal Supplement Series

Magnetohydrodynamic Model of Late Accretion onto a Protoplanetary Disk: Cloudlet Encounter Event [SSA]

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http://arxiv.org/abs/2303.14010


Recent observations suggest late accretion, which is generally nonaxisymmetric, onto protoplanetary disks. We investigated nonaxisymmetric late accretion considering the effects of magnetic fields. Our model assumes a cloudlet encounter event at a few hundred au scale, where a magnetized gas clump (cloudlet) encounters a protoplanetary disk. We studied how the cloudlet size and the magnetic field strength affect the rotational velocity profile in the disk after the cloudlet encounter. The results show that a magnetic field can either decelerate or accelerate the rotational motion of the cloudlet material, primarily depending on the relative size of the cloudlet to the disk thickness. When the cloudlet size is comparable to or smaller than the disk thickness, magnetic fields only decelerate the rotation of the colliding cloudlet material. However, if the cloudlet size is larger than the disk thickness, the colliding cloudlet material can be super-Keplerian as a result of magnetic acceleration. We found that the vertical velocity shear of the cloudlet produces a magnetic tension force that increases the rotational velocity. The acceleration mechanism operates when the initial plasma $\beta$ is $ \beta \lesssim 2\times 10^1 $. Our study shows that magnetic fields modify the properties of spirals formed by tidal effects. These findings may be important for interpreting observations of late accretion.

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M. Unno, T. Hanawa and S. Takasao
Mon, 27 Mar 23
21/59

Comments: 18 pages, 15 figures, 1 table, published in The Astrophysical Journal

The clumpy structure of $ε$ Eridani's debris disc revisited by ALMA [EPA]

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http://arxiv.org/abs/2303.13584


$\epsilon$ Eridani is the closest star to our Sun known to host a debris disc. Prior observations in the (sub-)millimetre regime have potentially detected clumpy structure in the disc and attributed this to interactions with an (as yet) undetected planet. However, the prior observations were unable to distinguish between structure in the disc and background confusion. Here we present the first ALMA image of the entire disc, which has a resolution of 1.6″$\times$1.2″. We clearly detect the star, the main belt and two point sources. The resolution and sensitivity of this data allow us to clearly distinguish background galaxies (that show up as point sources) from the disc emission. We show that the two point sources are consistent with background galaxies. After taking account of these, we find that resolved residuals are still present in the main belt, including two clumps with a $>3\sigma$ significance — one to the east of the star and the other to the northwest. We perform $n$-body simulations to demonstrate that a migrating planet can form structures similar to those observed by trapping planetesimals in resonances. We find that the observed features can be reproduced by a migrating planet trapping planetesimals in the 2:1 mean motion resonance and the symmetry of the most prominent clumps means that the planet should have a position angle of either ${\sim10^\circ}$ or ${\sim190^\circ}$. Observations over multiple epochs are necessary to test whether the observed features rotate around the star.

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M. Booth, T. Pearce, A. Krivov, et. al.
Mon, 27 Mar 23
29/59

Comments: 16 pages, 10 figures, accepted for publication in MNRAS

Predicting Physical Parameters of Cepheid and RR Lyrae variables in an Instant with Machine Learning [SSA]

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http://arxiv.org/abs/2303.13692


We present a machine learning method to estimate the physical parameters of classical pulsating stars such as RR Lyrae and Cepheid variables based on an automated comparison of their theoretical and observed light curve parameters at multiple wavelengths. We train artificial neural networks (ANNs) on theoretical pulsation models to predict the fundamental parameters (mass, radius, luminosity, and effective temperature) of Cepheid and RR Lyrae stars based on their period and light curve parameters. The fundamental parameters of these stars can be estimated up to 60 percent more accurately when the light curve parameters are taken into consideration. This method was applied to the observations of hundreds of Cepheids and thousands of RR Lyrae in the Magellanic Clouds to produce catalogs of estimated masses, radii, luminosities, and other parameters of these stars.

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A. Bhardwaj, E. Bellinger, S. Kanbur, et. al.
Mon, 27 Mar 23
30/59

Comments: Proceedings of IAU GA Symposium – Machine Learning in Astronomy: Possibilities and Pitfalls, in Busan, South Korea, 2022

Fast and Not-so-Furious: Case Study of the Fast and Faint Type IIb SN 2021bxu [HEAP]

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http://arxiv.org/abs/2303.13581


We present photometric and spectroscopic observations and analysis of SN~2021bxu (ATLAS21dov), a low-luminosity, fast-evolving Type IIb supernova (SN). SN~2021bxu is unique, showing a large initial decline in brightness followed by a short plateau phase. With $M_r = -15.93 \pm 0.16\, \mathrm{mag}$ during the plateau, it is at the lower end of the luminosity distribution of stripped-envelope supernovae (SE-SNe) and shows a distinct $\sim$10 day plateau not caused by H- or He-recombination. SN~2021bxu shows line velocities which are at least $\sim1500\,\mathrm{km\,s^{-1}}$ slower than typical SE-SNe. It is photometrically and spectroscopically similar to Type IIb SNe during the photospheric phases of evolution, with similarities to Ca-rich IIb SNe. We find that the bolometric light curve is best described by a composite model of shock interaction between the ejecta and an envelope of extended material, combined with a typical SN~IIb powered by the radioactive decay of $^{56}$Ni. The best-fit parameters for SN~2021bxu include a $^{56}$Ni mass of $M_{\mathrm{Ni}} = 0.029^{+0.004}{-0.005}\,\mathrm{M{\odot}}$, an ejecta mass of $M_{\mathrm{ej}} = 0.57^{+0.04}{-0.03}\,\mathrm{M{\odot}}$, and an ejecta kinetic energy of $K_{\mathrm{ej}} = 9.3^{+0.7}{-0.6} \times 10^{49}\, \mathrm{erg}$. From the fits to the properties of the extended material of Ca-rich IIb SNe we find a trend of decreasing envelope radius with increasing envelope mass. SN~2021bxu has $M{\mathrm{Ni}}$ on the low end compared to SE-SNe and Ca-rich SNe in the literature, demonstrating that SN~2021bxu-like events are rare explosions in extreme areas of parameter space. The progenitor of SN~2021bxu is likely a low mass He star with an extended envelope.

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D. Desai, C. Ashall, B. Shappee, et. al.
Mon, 27 Mar 23
32/59

Comments: 18 pages, 15 figures, submitted to MNRAS

SN 2019odp: A Massive Oxygen-Rich Type Ib Supernova [HEAP]

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http://arxiv.org/abs/2303.14146


We present and analyze observations of the Type Ib supernova (SN) 2019odp (a.k.a ZTF19abqwtfu) covering epochs within days of the explosion to the nebular phase at 360 d post-explosion. We discuss them in the context of recombination cooling emission for the early excess emission and consider progenitor models based on the nebular phase spectra. Our observations include photometric observations mainly in the optical and low to medium-resolution spectroscopic observations covering the complete observable time-range. We expand on existing methods to derive oxygen mass estimates from nebular phase spectroscopy. Our spectroscopic observations confirm the presence of He in the SN ejecta and we thus (re)classify it as a Type Ib supernova. From the pseudo-bolometric lightcurve we estimate a high ejecta mass $M_\text{ej} \sim 4 – 7~M_\odot$. The high ejecta mass, large nebular [O I]/[Ca II] line flux ratio ($1.2 – 1.9$) and an oxygen mass above $\gtrapprox 0.5\, M_\odot$ point towards a progenitor with pre-explosion mass higher than $18\,M_\odot$. The compact nature of the progenitor ($\lesssim 10\,R_\odot$) suggests a Wolf-Rayet (WR) star as progenitor.

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T. Schweyer, J. Sollerman, A. Jerkstrand, et. al.
Mon, 27 Mar 23
35/59

Comments: Submitted to A&A

Spectroscopic Signature of a Re-established Accretion Disk in Symbiotic-like Recurrent Nova RS Ophiuchi [HEAP]

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http://arxiv.org/abs/2303.14135


A novel method is presented which can pin down the time the accretion disk re-established itself in the RS Oph system after it experienced a nova disruption. The method is based on the re-ionisation of the ejecta by photoionisation from the radiation released in the boundary layer from accretion.

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A. Azzollini, S. Shore and P. Kuin
Mon, 27 Mar 23
36/59

Comments: 3 pages, 1 figure

Early phases of the Galaxy from the chemical imprint on the iron-poor stars J0815+4729 and J0023+0307 [GA]

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http://arxiv.org/abs/2303.14142


We have been exploring large spectroscopic databases such as SDSS to search for unique stars with extremely low iron content with the goal of extracting detailed information from the early phases of the Galaxy. We recently identified two extremely iron-poor dwarf stars J0815+4729 (Aguado et al. 2018a) and J0023+0307 (Aguado et al. 2018b) from SDSS/BOSS database and confirmed from high-quality spectra taken with ISIS and OSIRIS spectrographs at the 4.2m WHT and 10.4m GTC telescopes, respectively, located in La Palma (Canary Islands, Spain). We have also acquired high-resolution spectroscopy with UVES at 8.2m VLT telescope (Paranal, ESO, Chile) and HIRES at the 10m KeckI telescope (Mauna Kea, Hawaii, USA), uncovering the unique abundance pattern of these stars, that reveal e.g. the extreme CNO abundances in J0815+4729 with ratios [X/Fe]~$> 4$ (Gonz\’alez Hern\’andez et al. 2020). In addition, we are able to detect Li at the level of the lithium plateau in J0023+0307 (Aguado et al. 2019a), whereas we are only able to give a Li upper-limit 0.7 dex below the lithium plateau in J0815+4729, thus adding more complexity to the cosmological lithium problem. New upcoming surveys such as WEAVE, 4MOST and DESI will likely allow us to discover new interesting extremely iron-poor stars, that will certainly contribute to our understanding of the Early Galaxy, and the properties of the first stars and the first supernovae.

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J. Hernández, D. Aguado, C. Allende-Prieto, et. al.
Mon, 27 Mar 23
41/59

Comments: Accepted for publication in Memorie della Societ`a Astronomica Italiana

Glitches in solar-like oscillating F-type stars: Theoretical signature of the base of the convective envelope on the ratios $r_{010}$ [SSA]

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http://arxiv.org/abs/2303.14026


The transition between convective and radiative stellar regions is still not fully understood. The sharp variations in sound speed located in these transition regions give rise to a signature in specific seismic indicators, opening the possibility to constrain the physics of convection to radiation transition. Among those seismic indicators, the ratios of the small to large frequency separation for $l=0$ and $1$ modes ($r_{010}$) were shown to be particularly efficient to probe these transition regions. Interestingly, in the Kepler Legacy F-type stars, the oscillatory signatures left in the $r_{010}$ ratios by the sharp sound-speed variation have unexpected large amplitudes that still need to be explained. We show that the signature of the bottom of the convective envelope is amplified in the ratios $r_{010}$ by the frequency dependence of the amplitude compared to the signal seen in the frequencies themselves or the second differences. We find that among the different options of physical input investigated here, large amplitude signatures can only be obtained when convective penetration of the surface convective zone into the underlying radiative region is taken into account. In this case and even for amplitudes as large as those observed in F-type stars, the oscillating signature in the ratios can only be detected when the convective envelope is deep enough. This deep extension of the convective envelope causes doubt that the origin of the large amplitudes is due to penetrative convection as it is modelled here or implies that current stellar modelling (without penetrative convection) leads to an underestimation of the size of convective envelopes. In any case, studying the glitch signatures of a large number of oscillating F-type stars opens the possibility to constrain the physics of the stellar interior in these regions.

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M. Deal, M. Goupil, M. Cunha, et. al.
Mon, 27 Mar 23
54/59

Comments: 19 pages, 12 figures, accepted for publication in A&A

Herbig-Haro Flows and Young Stars in the Dobashi 5006 Dark Cloud [SSA]

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http://arxiv.org/abs/2303.13822


Two new Herbig-Haro flows were found in a study of the isolated Dobashi 5006 dark cloud (l$= 216^\circ.7$, b= $-$13$^\circ.9$): one certain (HH 1179) and one presumable, associated with the infrared sources 2MASS 06082284$-$0936139 and 2MASS 06081525$-$0933490, correspondingly. Judging from their spectral energy distributions, these sources may be Class 1 objects with luminosities of order 23 $L_{\odot}$ and 3.6 $L_{\odot}$ , respectively. They are part of the poor star cluster MWSC 0739, study of which based on data from the Gaia DR3 survey has made it possible to detect 17 stars which are probably members of it. A list of them and their main parameters is given. The distance of the cluster is estimated to be 820 pc and the color excess on the path to the cluster is E(BP-RP) $\approx$1.05 mag. All of these stars are PMS-objects and most of them are optically variable. It is concluded that the newly discovered compact star-formation zone in the Dobashi 5006 cloud has an age of no more than a few million years and this process continues up to the present time.

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T. Movsessian, T. Magakian, A. Rastorguev, et. al.
Mon, 27 Mar 23
57/59

Comments: N/A

Three-dimensional, Time-dependent MHD Simulation of Disk-Magnetosphere-Stellar Wind Interaction in a T Tauri, Protoplanetary System [SSA]

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http://arxiv.org/abs/2303.13238


We present a three-dimensional, time-dependent, MHD simulation of the short-term interaction between a protoplanetary disk and the stellar corona in a T Tauri system. The simulation includes the stellar magnetic field, self-consistent coronal heating and stellar wind acceleration, and a disk rotating at sub-Keplerian velocity to induce accretion. We find that initially, as the system relaxes from the assumed initial conditions, the inner part of the disk winds around and moves inward and close to the star as expected. However, the self-consistent coronal heating and stellar wind acceleration build up the original state after some time, significantly pushing the disk out beyond $10R_\star$. After this initial relaxation period, we do not find clear evidence of a strong, steady accretion flow funneled along coronal field lines, but only weak, sporadic accretion. We produce synthetic coronal X-ray line emission light curves which show flare-like increases that are not correlated with accretion events nor with heating events. These variations in the line emission flux are the result of compression and expansion due to disk-corona pressure variations. Vertical disk evaporation evolves above and below the disk. However, the disk – stellar wind boundary stays quite stable, and any disk material that reaches the stellar wind region is advected out by the stellar wind.

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O. Cohen, C. Garraffo, J. Drake, et. al.
Fri, 24 Mar 23
7/56

Comments: Accepted to ApJ, 12 pages, 11 figures

Coronal X-Ray Emission from Nearby, Low-Mass, Exoplanet Host Stars Observed by the MUSCLES and Mega-MUSCLES HST Treasury Survey Projects [SSA]

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http://arxiv.org/abs/2303.12929


The high energy X-ray and ultraviolet (UV) radiation fields of exoplanet host stars play a crucial role in controlling the atmospheric conditions and the potential habitability of exoplanets. Major surveys of the X-ray/UV emissions from late-type (K and M spectral type) exoplanet hosts have been conducted by the MUSCLES and Mega-MUSCLES Hubble Space Telescope (HST) Treasury programs. These samples primarily consist of relatively old, “inactive”, low mass stars. In this paper we present results from X-ray observations of the coronal emission from these stars obtained using the Chandra X-ray Observatory, the XMM-Newton Observatory, and the Neil Gehrels Swift Observatory. The stars effectively sample the coronal activity of low-mass stars at a wide range of masses and ages. The vast majority (21 of 23) of the stars are detected and their X-ray luminosities measured. Short-term flaring variability is detected for most of the fully-convective (M $\leq$ 0.35 M${\odot}$) stars but not for the more massive M dwarfs during these observations. Despite this difference, the mean X-ray luminosities for these two sets of M dwarfs are similar with more massive (0.35 M${\odot}$ $\leq$ M $\leq$ 0.6 M$_{\odot}$) M dwarfs at $\sim$5 $\times$ 10$^{26}$ erg s$^{-1}$ compared to $\sim$2 $\times$ 10$^{26}$ erg s$^{-1}$ for fully-convective stars older than 1 Gyr. Younger, fully-convective M dwarfs have X-ray luminosities between 3 and 6 $\times$ 10$^{27}$ erg s$^{-1}$.The coronal X-ray spectra have been characterized and provide important information that is vital for the modeling of the stellar EUV spectra.

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A. Brown, P. Schneider, K. France, et. al.
Fri, 24 Mar 23
8/56

Comments: 39 pages, 15 figures. Accepted for publication in The Astronomical Journal

On orbit performance of the solar flare trigger for the Hinode EUV Imaging Spectrometer [SSA]

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http://arxiv.org/abs/2303.13155


We assess the on-orbit performance of the flare event trigger for the Hinode EUV Imaging Spectrometer. Our goal is to understand the time-delay between the occurrence of a flare, as defined by a prompt rise in soft X-ray emission, and the initiation of the response observing study. Wide (266$”$) slit patrol images in the He II 256.32A spectral line are used for flare hunting, and a reponse is triggered when a pre-defined intensity threshold is reached. We use a sample of 13 $>$ M-class flares that succesfully triggered a response, and compare the timings with soft X-ray data from GOES, and hard X-ray data from RHESSI and Fermi. Excluding complex events that are difficult to interpret, the mean on orbit response time for our sample is 2 min 10 s, with an uncertainty of 84 s. These results may be useful for planning autonomous operations for future missions, and give some guidance as to how improvements could be made to capture the important impulsive phase of flares.

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D. Brooks, J. Reep, I. Ugarte-Urra, et. al.
Fri, 24 Mar 23
10/56

Comments: To be published as a Brief Report in Frontiers in Astronomy and Space Sciences

A spectacular jet from the bright 244-440 Orion proplyd: the MUSE NFM view [GA]

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http://arxiv.org/abs/2303.13205


In this work we present the highest spatial and spectral resolution integral field observations to date of the bipolar jet from the Orion proplyd 244-440 using MUSE NFM) observations on the VLT. We observed a previously unreported chain of six distinct knots in a roughly S-shaped pattern, and by comparing them with HST images we estimated proper motions in the redshifted knots of 9.5 mas yr$^{-1}$ with an inclination angle of $73^{\circ}$, though these quantities could not be measured for the blueshifted lobe. Analysis of the [FeII] and [NiII] lines suggests jet densities on the order of $\sim 10^5$ cm$^{-3}$. We propose that the observed S-shaped morphology originates from a jet launched by a smaller source with $M_\star < 0.2$ M${\odot}$ in orbital motion around a larger companion of $M\star \simeq 0.5$ M${\odot}$ at a separation of 30-40 au. The measured luminosities of the knots using the [OI]$\lambda6300$ and [SII]$\lambda6731$ lines were used to estimate a lower limit to the mass-loss rate in the jet of $1.3 \times 10^{-11}$ M${\odot}$ yr$^{-1}$ and an upper limit of $10^{-9}$ M$_{\odot}$ yr$^{-1}$, which is typical for low-mass driving sources. While the brightness asymmetry between the redshifted and blueshifted lobes is consistent with external irradiation, further analysis of the [NiII] and [FeII] lines suggests that photoionization of the jet is not likely to be a dominant factor, and that the emission is dominated by collisional excitation. The dynamical age of the jet compared to the anticipated survival time of the proplyd demonstrates that photoevaporation of the proplyd occurred prior to jet launching, and that this is still an active source. These two points suggest that the envelope of the proplyd may shield the jet from the majority of external radiation, and that photoionization of the proplyd does not appear to impact the ability of a star to launch a jet.

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A. Kirwan, C. Manara, E. Whelan, et. al.
Fri, 24 Mar 23
24/56

Comments: 30 pages, 20 figures

Effects of accretion on the Structure and Rotation of Forming Stars [SSA]

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http://arxiv.org/abs/2303.13184


Rotation period measurements of low-mass stars show that the spin distributions in young clusters do not exhibit the spin-up expected due to contraction, during the phase when a large fraction of stars are still surrounded by accretion discs. During this stage, the stars accrete mass and angular momentum and may experience accretion enhanced-magnetised winds. At the same time, the accretion of mass and energy has a significant impact on the evolution of stellar structure and moment of inertia. We compute evolution models of accreting very young stars and determine, in a self-consistent way, the effect of accretion on stellar structure and the angular momentum exchanges between the stars and their disc. We then vary the deuterium content, the accretion history, the entropy content of the accreted material, and the magnetic field as well as the efficiency of the accretion-enhanced winds. It comes that the models are driven alternatively both by the evolution of the momentum of inertia, and by the star-disc interaction torques. Of all the parameters we tested, the magnetic field strength, the accretion history and the Deuterium content have the largest impact. The injection of heat only plays a major role early in the evolution. This work demonstrates the importance of the moment of inertia’s evolution under the influence of accretion to explain the constant rotation rates distributions that are observed over the star-disc interactions. When accounting for rotation, the models computed with an up-to-date torque along with a consistent structural evolution of the accreting star are able to explain the almost constant spin evolution for the whole range of parameter we investigated, albeit only reproducing a narrow range around the median of the observed spin rate distributions.

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A. L. and M. S.P
Fri, 24 Mar 23
26/56

Comments: 13 pages, submitted version improved after 1st referee report, comments always welcome

Evolution of rotating massive stars with new hydrodynamic wind models [SSA]

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http://arxiv.org/abs/2303.13058


Mass loss due to line-driven winds is central to our understanding of the evolution of massive stars.
We extend the evolution models introduced in Paper I, where the mass loss recipe is based on the simultaneous calculation of the wind hydrodynamics and the line-acceleration, by incorporating the effects of stellar rotation. We introduce a grid of self-consistent line-force parameters for a set of standard evolutionary tracks. With that, we generate a new set of evolutionary tracks with rotation for $M_\text{ZAMS}=25,40,70,$ and $120\,M_\odot$, and metallicities $Z=0.014$ and $0.006$.
The self-consistent approach gives lower mass loss rates than the standard values adopted in previous evolution models. This decrease impacts strongly on the tracks of the most massive models. Weaker winds allow the star to retain more mass, but also more angular momentum. As a consequence, weaker wind models rotate faster and show a less efficient mixing in their inner stellar structure.
The new tracks predict an evolution of the rotational velocities through the MS in close agreement with the range of $\varv\sin i$ values found by recent surveys of Galactic O-type stars. As subsequent implications, the weaker winds from self-consistent models suggest a reduction of the contribution of the isotope $^{26}$Al to the ISM due to stellar winds of massive stars during the MS phase. Moreover, the higher luminosities found for the self-consistent evolutionary models suggest that some populations of massive stars might be less massive than previously thought, as in the case of Ofpe stars at the Galactic Centre. Therefore, this study opens a wide range of consequences for further research based on the evolution of massive stars.

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A. Gormaz-Matamala, J. Cuadra, G. Meynet, et. al.
Fri, 24 Mar 23
27/56

Comments: Accepted for publication in Astronomy & Astrophysics journal

Modeling of thermal and non-thermal radio emission from HH80-81 jet [GA]

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http://arxiv.org/abs/2303.13150


Protostellar jets are one of the primary signposts of star formation. A handful of protostellar objects exhibit radio emission from ionized jets, of which a few display negative spectral indices, indicating the presence of synchrotron emission. In this study, we characterize the radio spectra of HH80-81 jet with the help of a numerical model that we have developed earlier, which takes into account both thermal free-free and non-thermal synchrotron emission mechanisms. For modeling the HH80-81 jet, we consider jet emission towards the central region close to the driving source along with two Herbig-Haro objects, HH80 and HH81. We have obtained the best-fit parameters for each of these sources by fitting the model to radio observational data corresponding to two frequency windows taken across two epochs. Considering an electron number density in the range $10^3 – 10^5$ cm$^{-3}$, we obtained the thickness of the jet edges and fraction of relativistic electrons that contribute to non-thermal emission in the range $0.01^{\circ} – 0.1^{\circ}$ and $10^{-7} – 10^{-4}$, respectively. For the best-fit parameter sets, the model spectral indices lie in the range of -0.15 to +0.11 within the observed frequency windows.

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S. Mohan, S. Vig and S. Mandal
Fri, 24 Mar 23
29/56

Comments: 14 pages, 6 figures, Accepted for publication in the Journal of Astrophysics and Astronomy

Modulation of cosmic ray anti-protons in the heliosphere: simulations for a solar cycle [SSA]

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http://arxiv.org/abs/2303.13268


The precision measurements of galactic cosmic ray protons from PAMELA and AMS are reproduced using a well-established 3D numerical model for the period July 2006 – November 2019. The resulting modulation parameters are applied to simulate the modulation for cosmic antiprotons over the same period, which includes times of minimum modulation before and after 2009, maximum modulation from 2012 to 2015 including the reversal of the Sun’s magnetic field polarity, and the approach to new minimum modulation in 2020. Apart from their local interstellar spectra, the modulation of protons and antiprotons differ only in their charge-sign and consequent drift pattern. The lowest proton flux was in February-March 2014, but the lowest simulated antiproton flux is found to be in March-April 2015. These simulated fluxes are used to predict the proton to anti-proton ratios as a function of rigidity. The trends in these ratios contribute to clarify to a large extent the phenomenon of charge-sign dependence of heliospheric modulation during vastly different phases of the solar activity cycle. This is reiterated and emphasized by displaying so-called hysteresis loops. It is also illustrated how the values of the parallel and perpendicular mean free paths, as well as the drift scale, vary with rigidity over this extensive period. The drift scale is found to be at its lowest level during the polarity reversal period, while the lowest level of the mean free paths are found to be in March-April 2015.

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O. Aslam, M. Potgieter, X. Luo, et. al.
Fri, 24 Mar 23
30/56

Comments: 17 Pages, 7 Figures, Submitted to Astrophysical Journal

JOYS: JWST Observations of Young protoStars: Outflows and accretion in the high-mass star-forming region IRAS23385+605 [SSA]

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http://arxiv.org/abs/2303.13172


Aims: The JWST program JOYS (JWST Observations of Young protoStars) aims at characterizing the physical and chemical properties of young high- and low-mass star-forming regions, in particular the unique mid-infrared diagnostics of the warmer gas and solid-state components. We present early results from the high-mass star formation region IRAS23385+6053. Methods: The JOYS program uses the MIRI MRS with its IFU to investigate a sample of high- and low-mass star-forming protostellar systems. Results: The 5 to 28mum MIRI spectrum of IRAS23385+6053 shows a plethora of features. While the general spectrum is typical for an embedded protostar, we see many atomic and molecular gas lines boosted by the higher spectral resolution and sensitivity compared to previous space missions. Furthermore, ice and dust absorption features are also present. Here, we focus on the continuum emission, outflow tracers like the H2, [FeII] and [NeII] lines as well as the potential accretion tracer Humphreys alpha HI(7–6). The short-wavelength MIRI data resolve two continuum sources A and B, where mid-infrared source A is associated with the main mm continuum peak. The combination of mid-infrared and mm data reveals a young cluster in its making. Combining the mid-infrared outflow tracer H2, [FeII] and [NeII] with mm SiO data shows a complex interplay of at least three molecular outflows driven by protostars in the forming cluster. Furthermore, the Humphreys alpha line is detected at a 3-4sigma level towards the mid-infrared sources A and B. Following Rigliaco et al. (2015), one can roughly estimate accretion luminosities and corresponding accretion rates between ~2.6×10^-6 and ~0.9×10^-4 M_sun/yr. This is discussed in the context of the observed outflow rates. Conclusions: The analysis of the MIRI MRS observations for this young high-mass star-forming region reveals connected outflow and accretion signatures.

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H. Beuther, E. Dishoeck, L. Tychoniec, et. al.
Fri, 24 Mar 23
32/56

Comments: 12 pages, 9 figures, accepted for Astronomy & Astrophysics, the paper is also available at this https URL

Frequency analysis of the first-overtone RR Lyrae stars based on the Extended Aperture Photometry from the K2 data [SSA]

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http://arxiv.org/abs/2303.12884


Additional low-amplitude signals are observed in many RR Lyrae stars, beside the pulsations in radial modes. The most common ones are short-period signals forming a period ratio of around 0.60–0.65 with the first overtone, or long-period signals forming a period ratio of around 0.68. The RR Lyrae stars may also exhibit quasi-periodic modulation of the light curves, known as the Blazhko effect. We used the extensive sample of the first-overtone RR Lyrae stars observed by the Kepler telescope during the K2 mission to search for and characterize these low-amplitude additional signals. K2 data provides space-based photometry for a statistically significant sample. Hence this data is excellent to study in detail pulsation properties of RR Lyrae stars. We used K2 space-based photometry for RR Lyrae candidates from Campaigns 0-19. We selected RR Lyrae stars pulsating in the first overtone and performed a frequency analysis for each star to characterize their frequency contents. We classified 452 stars as first-overtone RR Lyrae. From that sample, we selected 281 RR${0.61}$ stars, 67 RR${0.68}$ stars, and 68 Blazhko stars. We found particularly interesting stars which show all of the above phenomena simultaneously. We detected signals in RR$_{0.61}$ stars that form period ratios lower than observed for the majority of stars. These signals likely form a new sequence in the Petersen diagram, around a period ratio of 0.60. In 32 stars we detected additional signals that form a period ratio close to that expected in RRd stars, but the classification of these stars as RRd is uncertain. We also report a discovery of additional signals in eight stars that form a new group in the Petersen diagram around the period ratio of 0.465-0.490. The nature of this periodicity remains unknown.

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H. Netzel, L. Molnar, E. Plachy, et. al.
Fri, 24 Mar 23
35/56

Comments: 29 pages, 29 figures, 4 tables, accepted for publication in A&A, full tables are available upon request before publication

Diffuse solar coronal features and their spicular footpoints [SSA]

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http://arxiv.org/abs/2303.13161


In addition to a component of the emission that originates from clearly distinguishable coronal loops, the solar corona also exhibits extreme-ultraviolet (EUV) and X-ray ambient emission that is rather diffuse and is often considered undesirable background. Importantly, unlike the generally more structured transition region and chromosphere, the diffuse corona appears to be rather featureless. The magnetic nature of the diffuse corona, and in particular, its footpoints in the lower atmosphere, are not well understood. We study the origin of the diffuse corona above the quiet-Sun network on supergranular scales. We identified regions of diffuse EUV emission in the coronal images from the SDO/AIA. To investigate their connection to the lower atmosphere, we combined these SDO/AIA data with the transition region spectroscopic data from the IRIS and with the underlying surface magnetic field information from the SDO/HMI. The region of the diffuse emission is of supergranular size and persists for more than five hours, during which it shows no obvious substructure. It is associated with plasma at about 1 MK that is located within and above a magnetic canopy. The canopy is formed by unipolar magnetic footpoints that show highly structured spicule-like emission in the overlying transition region. Our results suggest that the diffuse EUV emission patch forms at the base of long-ranging loops, and it overlies spicular structures in the transition region. Heated material might be supplied to it by means of spicular upflows, conduction-driven upflows from coronal heating events, or perhaps by flows originating from the farther footpoint. Therefore, the question remains open how the diffuse EUV patch might be sustained. Nevertheless, our study indicates that heated plasma trapped by long-ranging magnetic loops might substantially contribute to the featureless ambient coronal emission.

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N. Milanović, L. Chitta and H. Peter
Fri, 24 Mar 23
43/56

Comments: Article accepted for publication in A&A. Movie available at this https URL

GRB 191019A: a short gamma-ray burst in disguise from the disk of an active galactic nucleus [HEAP]

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http://arxiv.org/abs/2303.12935


Long and short gamma-ray bursts (GRBs), canonically separated at around 2 seconds duration, are associated with different progenitors: the collapse of a massive star and the merger of two compact objects, respectively. GRB 191019A was a long GRB ($T_{90}\sim64$ s). Despite the relatively small redshift z=0.248 and HST followup observations, an accompanying supernova was not detected. In addition, the host galaxy did not have significant star formation activity. Here we propose that GRB 191019A was produced by a binary compact merger, whose prompt emission was stretched in time by the interaction with a dense external medium. This would be expected if the burst progenitor was located in the disk of an active galactic nucleus, as supported by the burst localization close to the center of its host galaxy. We show that the light curve of GRB 191019A can be well modeled by a burst of intrinsic duration t=1.1 s and of energy $E_{\rm{iso}}=10^{51}$ erg seen moderately off-axis, exploding in a medium of density $10^7-10^8$ cm$^{-3}$. The double-peaked light curve carries the telltale features predicted for GRBs in high-density media, where the first peak is produced by the photosphere, and the second by the overlap of reverse shocks that take place before the internal shocks could happen. This would make GRB 191019A the first confirmed stellar explosion from within an accretion disk, with important implications for the formation and evolution of stars in accretion flows and for gravitational waves source populations.

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D. Lazzati, R. Perna, B. Gompertz, et. al.
Fri, 24 Mar 23
46/56

Comments: 6 pages, 2 figures. Submitted to ApJL

Observational Evidence of S-Web Source of the Slow Solar Wind [SSA]

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http://arxiv.org/abs/2303.12192


From 2022 March 18-21, active region (AR) 12967 was tracked simultaneously by Solar Orbiter (SO) at 0.35 au and Hinode/EIS at Earth. During this period, strong blue-shifted plasma upflows were observed along a thin, dark corridor of open field originating at the AR’s leading polarity and continuing towards the southern extension of the northern polar coronal hole. A potential field source surface (PFSS) model shows large lateral expansion of the open magnetic field along the corridor. Squashing factor Q-maps of the large scale topology further confirm super-radial expansion in support of the S-Web theory for the slow wind. The thin corridor of upflows is identified as the source region of a slow solar wind stream characterised by approx. 300 km s-1 velocities, low proton temperatures of approx. 5 eV, extremely high density over 100 cm-3, and a short interval of moderate Alfvenicity accompanied by switchback events. When connectivity changes from the corridor to the eastern side of the AR, the in situ plasma parameters of the slow wind indicate a distinctly different source region. These observations provide strong evidence that the narrow open field corridors, forming part of the S-Web, produce extreme properties in their associated solar wind streams.

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D. Baker, P. Demoulin, S. Yardley, et. al.
Thu, 23 Mar 23
1/67

Comments: Accepted ApJ

Hydrodynamical Evolution of Black-Hole Binaries Embedded in AGN Discs: III. The Effects of Viscosity [HEAP]

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http://arxiv.org/abs/2303.12207


Stellar-mass binary black holes (BBHs) embedded in active galactic nucleus (AGN) discs offer a distinct dynamical channel to produce black hole mergers detected in gravitational waves by LIGO/Virgo. To understand their orbital evolution through interactions with the disc gas, we perform a suite of 2D high-resolution, local shearing box, viscous hydrodynamical simulations of equal-mass binaries. We find that viscosity not only smooths the flow structure around prograde circular binaries, but also greatly raises their accretion rates. The overwhelming positive torque associated with the accretion dominates over the gravitational torque, and drives binary orbital expansion. However, retrograde binaries still experience rapid orbital decay, and prograde eccentric binaries still experience eccentricity damping, despite undergoing outspiral. Our numerical experiments further show that prograde binaries may experience inspiral if the physical sizes of the accretors are sufficiently small, such that the net binary accretion is reduced. Such a dependence of the binary accretion rate on the accretor size can be weaken through boosted accretion either due to a high viscosity or a more isothermal-like equation of state (EOS). Our results widen the explored parameter space for the hydrodynamics of embedded BBHs and demonstrate that their orbital evolution in AGN discs is a complex, multifaceted problem.

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R. Li and D. Lai
Thu, 23 Mar 23
3/67

Comments: 10 pages, 6 figures, submitted to MNRAS. arXiv admin note: text overlap with arXiv:2207.01125

Unveiling the chemical fingerprint of phosphorus-rich stars I. In the infrared region of APOGEE-2 [SSA]

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http://arxiv.org/abs/2303.12590


The origin of phosphorus, one of the essential elements for life on Earth, is currently unknown. Prevalent models of Galactic chemical evolution (GCE) underestimate the amount of P compared to observations. The recently discovered P-rich ([P/Fe] > 1 dex) and metal-poor giants further challenge current theories on stellar nucleosynthesis. Since the observed stars are low-mass giants, our primary goal is to find clues on their progenitor. By increasing the number of known P-rich stars, we aim to narrow down a reliable chemical abundance pattern and to place robust constraints on the responsible nucleosynthetic mechanism. In the long term, identifying the progenitor of the P-rich stars may contribute to the search for the source of P in our Galaxy. We performed a detailed chemical abundance analysis based on the H-band spectra from APOGEE-2 (DR17). Employing the BACCHUS code, we measured the abundances of 13 elements in the sample, which is mainly composed of a recent collection of Si-enhanced giants. We also analyzed the orbital motions and compared the abundance results to possible nucleosynthetic formation scenarios, as well as to detailed GCE models. We enlarged the sample of confirmed P-rich stars from 16 to 78 giants, representing the largest sample of P-rich stars to date. Significant enhancements in O, Al, Si and Ce, as well as systematic correlations among the elements, unveil the chemical fingerprint of the P-rich stars. The high Mg and C+N found in some of the P-rich stars with respect to P-normal stars is not confirmed over the full sample. Strikingly, the strong over-abundance in the $\alpha$-element Si is accompanied by normal Ca and S abundances. Our analysis of the orbital motion showed that the P-rich stars do not belong to a specific sub-population. In addition, we confirm that the majority of the sample stars are not part of binary systems.

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M. Brauner, T. Masseron, D. García-Hernández, et. al.
Thu, 23 Mar 23
4/67

Comments: 29 pages, 18 figures, 8 tables, accepted for publication in Astronomy & Astrophysics

Neutron Skin Thickness Dependence of Astrophysical $S$-factor [CL]

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http://arxiv.org/abs/2303.12156


Background: The density dependence of nuclear symmetry energy is crucial in determining several properties of finite nuclei to the neutron stars with mass $\sim$ 1.4 $M_\odot$. The values of neutron skin thickness, isovector giant dipole resonances energies and various nuclear reaction cross-sections in asymmetric nuclei have been utilized to determine the slope of symmetry energy ($L_0$) at the saturation density. Recent PREX-II and CREX measurements of neutron skin thickness in $^{208}$Pb and $^{48}$Ca nuclei yield very different values of $L_0$ which overlap marginally within 90$\%$ confidence interval.
Purpose: Our objective is to demonstrate the role of symmetry energy on the sub-barrier fusion cross-section and the astrophysical $S$-factor for asymmetric nuclei.
Method: The nucleus nucleus potentials are generated using the double folding model (DFM) for three different nucleon-nucleon interactions. These DFM potentials are used for the calculation of the sub-barrier fusion cross-section and the astrophysical $S$-factor. The nucleon densities required for DFM potentials are generated from different families of non-relativistic and relativistic mean-field models which correspond to a wide range of neutron skin thickness or $L_0$.
Results: We have calculated the sub-barrier fusion cross-section for several asymmetric nuclei involving O, Ca, Ni, and Sn isotopes. The results are presented for the barrier parameters, cross-section, and astrophysical $S$-factor for $^{54}$Ca+$^{54}$Ca and $^{124}$Sn+$^{124}$Sn as a function of neutron skin thickness.
Conclusions: The cross-section for the neutron-rich nuclei show a strong dependence on the behavior of symmetry energy or the neutron skin thickness. The increase in skin thickness lowers the height of the barrier as well as its width which enhances the values of the $S$-factor by more than an order of magnitude.

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T. Ghosh, S. Sangeeta, G. Saxena, et. al.
Thu, 23 Mar 23
6/67

Comments: 8 pages, 7 figures

X-Shooting ULLYSES: Massive stars at low metallicity. III. Terminal wind speeds of ULLYSES massive stars [SSA]

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http://arxiv.org/abs/2303.12165


The winds of massive stars have an impact on stellar evolution and on the surrounding medium. The maximum speed reached by these outflows, the terminal wind speed, is a global wind parameter and an essential input for models of stellar atmospheres and feedback. With the arrival of the ULLYSES programme, a legacy UV spectroscopic survey with HST, we have the opportunity to quantify the wind speeds of massive stars at sub-solar metallicity (in the Large and Small Magellanic Clouds, 0.5Z and 0.2Z) at an unprecedented scale. We empirically quantify the wind speeds of a large sample of OB stars, including supergiants, giants, and dwarfs at sub-solar metallicity. Using these measurements, we investigate trends of terminal wind speed with a number of fundamental stellar parameters, namely effective temperature, metallicity, and surface escape velocity. We empirically determined the terminal wind speed for a sample of 149 OB stars in the Magellanic Clouds either by directly measuring the maximum velocity shift of the absorption component of the Civ 1548-1550 line profile, or by fitting synthetic spectra produced using the Sobolev with exact integration method. Stellar parameters were either collected from the literature, obtained using spectral-type calibrations, or predicted from evolutionary models. We find strong trends of terminal wind speed with effective temperature and surface escape speed when the wind is strong enough to cause a saturated P Cygni profile in Civ 1548-1550. We find evidence for a metallicity dependence on the terminal wind speed proportional to Z^0.22+-0.03 when we compared our results to previous Galactic studies. Our results suggest that effective temperature rather than surface escape speed should be used as a straightforward empirical prediction of terminal wind speed and that the observed metallicity dependence is steeper than suggested by earlier works.

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C. Hawcroft, H. Sana, L. Mahy, et. al.
Thu, 23 Mar 23
15/67

Comments: 21 pages, 16 figures, 8 tables. Accepted in A&A

N-body simulation of binary star mass transfer using NVDIA GPUs [SSA]

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http://arxiv.org/abs/2303.12166


Binary star systems are of particular interest to astronomers because they can be used as astrophysical laboratories to study the properties and processes of stars. Between 70% to 90% of the stars in our galaxy are part of a binary star system. Among the many types of binary systems observed, the dynamics of semi-detached and contact systems are the most interesting because they exhibit mass transfer, which changes the composition and life cycle of both stars. The time scales of the mass transfer process are extremely large which makes the process impossible to capture through physical observation. Computer simulations have proved invaluable in refining our understanding of the mass transfer processes. Here we introduce an intuitive, computationally efficient, gravity centered model that simulates the filling of the Roche lobe of an expanding star and its transfer of mass through the first Lagrangian point.

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S. Goderya, E. Smith, B. Fain, et. al.
Thu, 23 Mar 23
17/67

Comments: N/A

Inhomogeneous Galactic Chemical Evolution: Modelling Ultra-Faint Dwarf Galaxies of the Large Magellanic Cloud [GA]

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http://arxiv.org/abs/2303.12530


Ultra-faint dwarf galaxies are among the oldest and most metal-poor galaxies in the cosmos, observed to contain no traces of gas at the present time and a high dark matter mass fraction. Understanding the chemical abundance dispersion in such extreme environments could shed light on the properties of the first generations of stars in the cosmos. We present a novel inhomogeneous chemical evolution model, i-GEtool, that we apply to two ultra-faint dwarf galaxies, Carina II (Car II) and Reticulum II (Ret II), which are satellites of the Large Magellanic Cloud. In summary, our model is based on the Monte Carlo sampling of the initial mass function as star formation proceeds in different gas cells of the simulated galaxy volume. We account for the chemical enrichment of Supernova bubbles as they spread in the interstellar medium, which causes dispersion in the predicted elemental abundances. We recreate the elemental abundance patterns by focusing on $\alpha$- and odd-$\textit{Z}$ elements, predicting two sequences in [C/Fe] and [N/Fe] at all metallicities. Our models systematically underestimate [C/Fe] and [Ti/Fe] because of the large uncertainty in the adopted stellar nucleosynthesis yields. We discuss that the observed C and N abundances had likely been affected by internal mixing processes, which changed the initial surface abundances in the red giants. Our Supernova feedback scheme is responsible for driving galactic outflows, which quench the star formation activity in the simulated galaxies at early times. The average outflow mass-loading factor as predicted by our models is $\approx 10^{3}$, which extrapolates towards very low galaxy stellar masses the trend observed at high stellar masses. Finally, by combining our model with the MIST isochrone database, we draw synthetic colour-magnitude diagrams of Car II and Ret II and compare them to observations.

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R. Alexander, F. Vincenzo, A. Ji, et. al.
Thu, 23 Mar 23
18/67

Comments: 18 Pages, 11 Figures, 2 Tables

Asteroseismic age constraints on the open cluster NGC 2477 using oscillating stars identified with TESS FFI [SSA]

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http://arxiv.org/abs/2303.12205


The ages of pulsating stars in clusters can be determined by isochrone fitting and it can be further improved by asteroseismic modelling. We analyse the intermediate-age open cluster NGC2477, known to suffer from differential extinction, to explore if asteroseismology and clusters characteristics can help understand the metallicity, extinction and result in better age determinations than isochrone-fitting alone. We combine a multitude of recent observations from Gaia, high-resolution spectroscopy, and extinction maps to analyse the cluster and then search for and detect variability in the member stars using TESS FFI data. To interpret all of these data, we used stellar structure, evolution and oscillation codes. We performed an isochrone fitting to the cluster using publically-available isochrones, which provides a cluster age of between 0.6 to 1.1 Ga. Then using TESS Full-frame images, we analysed the time dimension of the members of this cluster. We created optimised pixel light curves using the ${\tt tessipack}$ package which allows us to consider possible contamination by nearby stars. Using these light curves, we identified many interesting levels of variability of stars in this cluster, including binaries and oscillating stars. For the asteroseismic analysis, we selected a few uncontaminated A–F type oscillating stars and used the MESA and GYRE codes to interpret the frequency signals. By comparing the theoretical and the observed spectra, we identified frequency separations, $\Delta\nu$, for four stars. Then using the identified $\Delta\nu$ and imposing that the best matched theoretical models have the same age, metallicity and background extinction, we constrained the cluster’s age to 1.0 $\pm$ 0.1 Ga. We conclude that using the TESS FFI data, we can identify oscillating stars in clusters, which allows us to better refine their ages.

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D. Palakkatharappil and O. Creevey
Thu, 23 Mar 23
24/67

Comments: 26 pages, 30 figures; accepted for publication in A&A

The carbon star DY Persei may be a cool R Coronae Borealis variable [SSA]

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http://arxiv.org/abs/2303.12436


Optical and near-IR photometry suggests that the carbon star DY Persei exhibits fadings similar to those of R Coronae Borealis (RCB) variables. Photometric surveys of the Galaxy and Magellanic Clouds uncovered new DY Per variables with infrared photometry identifying them with cool carbon stars, perhaps, with an unusual tendency to shed mass. In an attempt to resolve DY Per’s identity crisis — a cool carbon giant or a cool RCB variable? — we analyze a high-resolution H&K band spectrum of DY Per. The CO first-overtone bands in the K-band of DY Per show a high abundance of 18O such that 16O/18O = 4 +- 1, a ratio sharply at odds with published results for `regular’ cool carbon giants with 16O/18O ~ 1000 but this exceptionally low ratio is characteristic of RCB-variables and HdC stars. This similarity suggests that DY Per indeed may be a cool RCB variable. Current opinion considers RCB-variables to result from merger of a He onto a CO white dwarf; observed abundances of these H-deficient stars including the exceptionally low 16O/18O ratios are in fair accord with predicted compositions for white dwarf merger products. A H-deficiency for DY Per is not directly observable but is suggested from the strength of a HF line and an assumption that F may be overabundant, as observed and predicted for RCB stars.

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D. Garcia-Hernandez, N. Rao, D. Lambert, et. al.
Thu, 23 Mar 23
27/67

Comments: Accepted for publication in ApJ (16 pages and 4 figures)

Data driven analysis of cosmic rays in the heliosphere: diffusion of cosmic protons [HEAP]

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http://arxiv.org/abs/2303.12239


Understanding the time-dependent relationship between the Sun’s variability and cosmic rays (GCR) is essential for developing predictive models of energetic radiation in space. When traveling inside the heliosphere, GCRs are affected by magnetic turbulence and solar wind disturbances which result in the so-called solar modulation effect. To investigate this phenomenon, we have performed a data-driven analysis of the temporal dependence of the GCR flux over the solar cycle. With a global statistical inference of GCR data collected in space by AMS-02 and PAMELA on monthly basis, we have determined the rigidity and time dependence of the GCR diffusion mean free path. Here we present our results for GCR protons, we discuss their interpretation in terms of basic processes of particle transport and their relations with the dynamics of the heliospheric plasma.

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N. Tomassetti, E. Fiandrini, B. Bertucci, et. al.
Thu, 23 Mar 23
37/67

Comments: 5 pages, 4 figures, comments welcome

Convective boundary mixing in main-sequence stars: theory and empirical constraints [SSA]

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http://arxiv.org/abs/2303.12099


The convective envelopes of solar-type stars and the convective cores of intermediate- and high-mass stars share boundaries with stable radiative zones. Through a host of processes we collectively refer to as “convective boundary mixing” (CBM), convection can drive efficient mixing in these nominally stable regions. In this review, we discuss the current state of CBM research in the context of main-sequence stars through three lenses. (1) We examine the most frequently implemented 1D prescriptions of CBM — exponential overshoot, step overshoot, and convective penetration — and we include a discussion of implementation degeneracies and how to convert between various prescriptions. (2) Next, we examine the literature of CBM from a fluid dynamical perspective, with a focus on three distinct processes: convective overshoot, entrainment, and convective penetration. (3) Finally, we discuss observational inferences regarding how much mixing should occur in the cores of intermediate- and high-mass stars, and the implied constraints that these observations place on 1D CBM implementations. We conclude with a discussion of pathways forward for future studies to place better constraints on this difficult challenge in stellar evolution modeling.

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E. Anders and M. Pedersen
Thu, 23 Mar 23
39/67

Comments: Accepted for publication as an invited review in the Galaxies special issue, “The Structure and Evolution of Stars” (see this https URL). Supplementary materials including MESA inlists and collected data used to generate some figures can be found online in a Zenodo repository at this https URL

3D Radiation-Hydrodynamic Simulations Resolving Interior of Rapidly Accreting Primordial Protostar [GA]

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http://arxiv.org/abs/2303.12100


Direct collapse of supermassive stars is a possible pathway to form supermassive black hole seeds at high redshifts. Whereas previous three-dimensional (3D) simulations demonstrate that supermassive stars form via rapid mass accretion, those resolving the stellar interior have been limited. We here report 3D radiation-hydrodynamic (RHD) simulations following the evolution of rapidly accreting protostars resolving the stellar interior. We use an adaptive mesh refinement code with our newly developed RHD solver employing an explicit M1 closure method. We follow the early evolution until the stellar mass reaches $\sim 10~M_\odot$ from two different initial configurations of spherical and turbulent clouds. We demonstrate that, in both the cases, a swollen protostar whose radius is $100\mathrm{-}1000~R_\odot$ appears, as predicted by the stellar evolution calculations. Its effective temperature remains a few thousand Kelvin, and the radiative feedback by ionizing photons is too weak to disturb the accretion flow up to the epoch examined in this work. In the turbulent case, the protostar rotates rapidly at more than 0.4 times the Keplerian velocity owing to the angular momentum provided by the initial turbulence. The protostar approximates an oblate spheroid, and its equatorial radius is more than twice the polar radius. Our results suggest that we need to consider the rapid stellar rotation to elucidate the realistic 3D protostellar evolution in the supermassive star formation.

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K. Kimura, T. Hosokawa, K. Sugimura, et. al.
Thu, 23 Mar 23
43/67

Comments: 9 pages, 5 figures, submitted to ApJL

The orbital and physical properties of five southern Be+sdO binary systems [SSA]

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http://arxiv.org/abs/2303.12616


Close binary interactions may play a critical role in the formation of the rapidly rotating Be stars. Mass transfer can result in a mass gainer star spun up by the accretion of mass and angular momentum, while the mass donor is stripped of its envelope to form a hot and faint helium star. FUV spectroscopy has led to the detection of about 20 such binary Be+sdO systems. Here we report on a three-year program of high quality spectroscopy designed to determine the orbital periods and physical properties of five Be binary systems. These binaries are long orbital period systems with $P =$ 95 to 237 days and with small semi-amplitude $K_1<11$ km s$^{-1}$. We combined the Be star velocities with prior sdO measurements to obtain mass ratios. A Doppler tomography algorithm shows the presence of the He II $\lambda 4686$ line in the faint spectrum of the hot companion in four of the targets. We discuss the observed line variability and show evidence of phased-locked variations in the emission profiles of HD 157832, suggesting a possible disk spiral density wave due to the presence of the companion star. The stripped companions in HD 113120 and HD 137387 may have a mass larger than the 1.4 $M_\odot$ indicating that they could be progenitors of Type Ib and Ic supernovae.

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L. Wang, D. Gies, G. Peters, et. al.
Thu, 23 Mar 23
46/67

Comments: 50 pages, 23 figures, 16 tables

Physical Models for Solar Cycle Predictions [SSA]

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http://arxiv.org/abs/2303.12648


The dynamic activity of stars such as the Sun influences (exo)planetary space environments through modulation of stellar radiation, plasma wind, particle and magnetic fluxes. Energetic stellar phenomena such as flares and coronal mass ejections act as transient perturbations giving rise to hazardous space weather. Magnetic fields — the primary driver of stellar activity — are created via a magnetohydrodynamic dynamo mechanism within stellar convection zones. The dynamo mechanism in our host star — the Sun — is manifest in the cyclic appearance of magnetized sunspots on the solar surface. While sunspots have been directly observed for over four centuries, and theories of the origin of solar-stellar magnetism have been explored for over half a century, the inability to converge on the exact mechanism(s) governing cycle to cycle fluctuations and inconsistent predictions for the strength of future sunspot cycles have been challenges for models of solar cycle forecasts. This review discusses observational constraints on the solar magnetic cycle with a focus on those relevant for cycle forecasting, elucidates recent physical insights which aid in understanding solar cycle variability, and presents advances in solar cycle predictions achieved via data-driven, physics-based models. The most successful prediction approaches support the Babcock-Leighton solar dynamo mechanism as the primary driver of solar cycle variability and reinforces the flux transport paradigm as a useful tool for modelling solar-stellar magnetism.

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P. Bhowmik, J. Jiang, L. Upton, et. al.
Thu, 23 Mar 23
52/67

Comments: 50 pages, 7 figures, submitted to Space Science Reviews

Turbulent processes and mean-field dynamo [SSA]

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http://arxiv.org/abs/2303.12425


Mean-field dynamo theory has important applications in solar physics and galactic magnetism. We discuss some of the many turbulence effects relevant to the generation of large-scale magnetic fields in the solar convection zone. The mean-field description is then used to illustrate the physics of the $\alpha$ effect, turbulent pumping, turbulent magnetic diffusivity, and other effects on a modern solar dynamo model. We also discuss how turbulence transport coefficients are derived from local simulations of convection and then used in mean-field models.

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A. Brandenburg, D. Elstner, Y. Masada, et. al.
Thu, 23 Mar 23
55/67

Comments: 64 pages, 20 figures, 2 tables, submitted to Space Science Reviews, special issue “Solar and stellar dynamos: a new era”. arXiv admin note: substantial text overlap with arXiv:2206.06566

Disks around young planetary-mass objects: Ultradeep Spitzer imaging of NGC1333 [SSA]

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http://arxiv.org/abs/2303.12451


We report on a sensitive infrared search for disks around isolated young planetary-mass objects (PMOs) in the NGC1333 cluster, by stacking 70 Spitzer/IRAC frames at 3.6 and 4.5$\,\mu m$. Our co-added images go >2.3 mag deeper than single-epoch frames, and cover 50 brown dwarfs, 15 of which have M9 or later spectral types. Spectral types >M9 correspond to masses in the giant planet domain, i.e., near or below the Deuterium-burning limit of 0.015 Msol. Five of the 12 PMOs show definitive evidence of excess, implying a disk fraction of 42%, albeit with a large statistical uncertainty given the small sample. Comparing with measurements for higher-mass objects, the disk fraction does not decline substantially with decreasing mass in the sub-stellar domain, consistent with previous findings. Thus, free-floating PMOs have the potential to form their own miniature planetary systems. We note that only one of the six lowest-mass objects in NGC1333, with spectral type L0 or later, has a confirmed disk. Reviewing the literature, we find that the lowest mass free-floating objects with firm disk detections have masses ~0.01 Msol (or ~10 MJup). It is not clear yet whether even lower mass objects harbor disks. If not, it may indicate that ~10 MJup is the lower mass limit for objects that form like stars. Our disk detection experiment on deep Spitzer images paves the way for studies with JWST at longer wavelengths and higher sensitivity, which will further explore disk prevalence and formation of free-floating PMOs.

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A. Scholz, K. Muzic, R. Jayawardhana, et. al.
Thu, 23 Mar 23
56/67

Comments: 14 pages, 3 figures, 1 table. Accepted for publication in AJ

New constraints on the presence of debris disks around G 196-3 B and VHS J125601.92-125723.9 b [EPA]

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http://arxiv.org/abs/2303.12163


We obtained deep images of G 196-3 B and VHS J1256-1257 b with the NOrthern Extended Millimeter Array (NOEMA) at 1.3 mm. These data were combined with recently published Atacama Large Millimeter Array (ALMA) and Very Large Array (VLA) data of VHS J1256-1257 b at 0.87 mm and 0.9 cm, respectively. Neither G 196-3 B nor VHS J1256-1257 b were detected in the NOEMA, ALMA and VLA data. At 1.3 mm, we imposed flux upper limits of 0.108 mJy (G 196-3 B) and 0.153 mJy (VHS J1256-1257 b) with a 3-sigma confidence. Using the flux upper limits at the millimeter and radio wavelength regimes, we derived maximum values of 0.016 M${\rm Earth}$ and 0.004 M${\rm Earth}$ for the mass of any cold dust that might be surrounding G 196-3 B and VHS J1256-1257 b, respectively. We put our results in the context of other deep millimeter observations of free-floating and companion objects with substellar masses smaller than 20 M$_{\rm Jupiter}$ and ages between 1 and a few hundred million years. Only two very young objects are detected out of a few tens concluding, as other groups did before, that the disks around these very low-mass objects must have small masses and possibly reduced sizes. If debris disks around substellar objects scale down in a similar manner as protoplanetary disks do, millimeter observations of moderately young brown dwarfs and planets must be at least two orders of magnitude deeper for being able to detect and characterize their surrounding debris disks.

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O. Zakhozhay, M. Osorio, V. Bejar, et. al.
Thu, 23 Mar 23
57/67

Comments: Accepted fro publication in A&A

Mixing of materials in magnetised core-collapse supernova remnants [SSA]

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http://arxiv.org/abs/2303.12579


Core-collapse supernova remnants are structures of the interstellar medium (ISM) left behind the explosive death of most massive stars (smaller or equal to 40 Mo). Since they result in the expansion of the supernova shock wave into the gaseous environment shaped by the star wind history, their morphology constitutes an insight into the past evolution of their progenitor star. Particularly, fast-moving massive stars can produce asymmetric core-collapse supernova remnants. We investigate the mixing of materials in core-collapse supernova remnants generated by a moving massive 35 Mo star, in a magnetised ISM. Stellar rotation and the wind magnetic field are time-dependently included into the models which follow the entire evolution of the stellar surroundings from the zero age main sequence to 80 kyr after the supernova explosion. It is found that very little main sequence material is present in remnants from moving stars, that the Wolf-Rayet wind mixes very efficiently within the 10 kyr after the explosion, while the red supergiant material is still unmixed by 30 per cent within 50 kyr after the supernova. Our results indicate that the faster the stellar motion, the more complex the internal organisation of the supernova remnant and the more effective the mixing of ejecta therein. In contrast, the mixing of stellar wind material is only weakly affected by progenitor motion, if at all.

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M. M.-A., P. M., P. M., et. al.
Thu, 23 Mar 23
58/67

Comments: Accepted at MNRAS

Inferring the progenitor mass-kinetic energy relation of stripped-envelope core-collapse supernovae from nebular spectroscopy [HEAP]

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http://arxiv.org/abs/2303.12432


The relation between the progenitor mass and the kinetic energy of the explosion is a key toward revealing the explosion mechanism of stripped-envelope (SE) core-collapse (CC) supernovae (SNe). Here, we present a method to derive this relation using the nebular spectra of SESNe, based on the correlation between the [O~I]/[Ca~II], which is an indicator of the progenitor mass, and the width of [O~I], which measures the expansion velocity of the oxygen-rich material. To explain the correlation, the kinetic energy ($E_{\rm K}$) is required to be positively correlated with the progenitor mass as represented by the CO core mass ($M_{\rm CO}$). We demonstrate that SNe IIb/Ib and SNe Ic/Ic-BL follow the same $M_{\rm CO}$-$E_{\rm K}$ scaling relation, which suggests the helium-rich and helium-deficient SNe share the same explosion mechanism. The $M_{\rm CO}$-$E_{\rm K}$ relation derived in this work is compared with the ones from early phase observations. The results are largely in good agreement. Combined with early phase observation, the method presented in this work provides a chance to scan through the ejecta from the outermost region to the dense inner core, which is important to reveal the global properties of the ejecta and constrain the explosion mechanism of core-collapse supernovae.

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Q. Fang and K. Maeda
Thu, 23 Mar 23
61/67

Comments: 18 pages, 13 figures. Accepted for publication in ApJ

The first stars: formation, properties, and impact [CEA]

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http://arxiv.org/abs/2303.12500


The first generation of stars, often called Population III (or Pop III), form from metal-free primordial gas at redshifts 30 and below. They dominate the cosmic star formation history until redshifts 15 to 20, at which point the formation of metal-enriched Pop II stars takes over. We review current theoretical models for the formation, properties and impact of Pop III stars, and discuss existing and future observational constraints. Key takeaways from this review include the following: (1) Primordial gas is highly susceptible to fragmentation and Pop III stars form as members of small clusters with a logarithmically flat mass function. (2) Feedback from massive Pop III stars plays a central role in regulating subsequent star formation, but major uncertainties remain regarding its immediate impact. (3) In extreme conditions, supermassive Pop III stars can form, reaching masses of several 10^5 Msun. Their remnants may be the seeds of the supermassive black holes observed in high-redshift quasars. (4) Direct observations of Pop III stars in the early Universe remain extremely challenging. Indirect constraints from the global 21cm signal or gravitational waves are more promising. (5) Stellar archeological surveys allow us to constrain both the low-mass and the high-mass ends of the Pop III mass distribution. Observations suggest that most massive Pop III stars end their lives as core-collapse supernovae rather than as pair-instability supernovae.

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R. Klessen and S. Glover
Thu, 23 Mar 23
65/67

Comments: To appear in Annual Reviews of Astronomy and Astrophysics (75 pages, 14 figures, 500+ references)

Recommending Low-Cost Compact Space Environment and Space Weather Effects Sensor Suites for NASA Missions [IMA]

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http://arxiv.org/abs/2303.11875


As miniaturized spacecraft (e.g., cubesats and smallsats) and instrumentation become an increasingly indispensable part of space exploration and scientific investigations, it is important to understand their potential susceptibility to space weather impacts resulting from the sometimes volatile space environment. There are multitude of complexities involved in how space environment interacts with different space hardware/electronics. Measurements of such impacts, however, have been lacking. Therefore, we recommend developing and/or procuring low-cost, low-power consumption, and compact sensor suites (mainly for space weather and impact purposes) and flying them on all future NASA (and U.S in general) missions in order to measure and quantify space weather impacts, in addition to the main instrumentation.

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Y. Zheng, M. Xapsos, I. Jun, et. al.
Wed, 22 Mar 23
1/68

Comments: White paper submitted to Decadal Survey for Solar and Space Physics (Heliophysics) 2024-2033 It can also be accessed here. this http URL

Evolving ONe WD+He WD systems to ultra-compact X-ray binaries [SSA]

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http://arxiv.org/abs/2303.11571


It has been proposed that accretion-induced collapse (AIC) of massive white dwarfs (WDs) is an indispensable path for the formation of neutron star (NS) binaries. Although there are still no direct evidence for the existence of AIC events, several kinds of NS systems are suggested to originate from the AIC processes. One of the representative evidence is the detection of the strong magnetic field and slow spin NSs with ultra-light companions (<=0.1 Msun) in close orbits. However, previous studies cannot explain the formation of AIC events with such low-mass companions. In the present work, we evolve a series of ONe WD+He WD systems to the formation of AIC events (named as the He WD donor channel), and the NS binaries behave as ultra-compact X-ray binaries when the He WDs refill their Roche-lobes. We found that the ONe WD+He WD systems a possible channel for the formation of the newly formed NS+ultra-light companion systems just after the AIC event. Although there are some other inconsistent properties, the detected companion mass and orbital period of 4U 1626-67 (one of the newly formed NS binaries with ultra-light companions) can be reproduced by the He WD donor channel. In addition, combined with previous asteroseismology results, we speculate that an UCXB source (XTE J1751-305) may originate from the He WD donor channel.

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D. Liu and B. Wang
Wed, 22 Mar 23
2/68

Comments: 13 pages, 5 figures, accepted for the publication of MNRAS

Discovery of a massive giant planet with extreme density around a sub-giant star TOI-4603 [EPA]

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http://arxiv.org/abs/2303.11841


We present the discovery of a transiting massive giant planet around TOI-4603, a sub-giant F-type star from NASA’s Transiting Exoplanet Survey Satellite (TESS). The newly discovered planet has a radius of $1.042^{+0.038}{-0.035}$ $R{J}$, and an orbital period of $7.24599^{+0.00022}{-0.00021}$ days. Using radial velocity measurements with the PARAS {and TRES} spectrographs, we determined the planet’s mass to be $12.89^{+0.58}{-0.57}$ $M_{J}$, resulting in a bulk density of $14.1^{+1.7}{-1.6}$ g ${cm^{-3}}$. This makes it one of the few massive giant planets with extreme density and lies in the transition mass region of massive giant planets and low-mass brown dwarfs, an important addition to the population of less than five objects in this mass range. The eccentricity of $0.325\pm0.020$ and an orbital separation of $0.0888\pm0.0010$ AU from its host star suggest that the planet is likely undergoing high eccentricity tidal (HET) migration. We find a fraction of heavy elements of $0.13^{+0.05}{-0.06}$ and metal enrichment of the planet ($Z_{P}/Z_{star}$) of $4.2^{+1.6}_{-2.0}$. Detection of such systems will offer us to gain valuable insights into the governing mechanisms of massive planets and improve our understanding of their dominant formation and migration mechanisms.

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A. Khandelwal, R. Sharma, A. Chakraborty, et. al.
Wed, 22 Mar 23
4/68

Comments: accepted for publication in A&A Letters

Forming super-Mercuries: The role of stellar abundances [EPA]

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http://arxiv.org/abs/2303.11948


Super-Mercuries, rocky exoplanets with bulk iron mass fraction of more than 60 per cent, appear to be preferentially hosted by stars with higher iron mass fraction than the Earth. It is unclear whether these iron-rich planets can form in the disc, or if giant impacts are necessary. Here we investigate the formation of super-Mercuries in their natal protoplanetary discs by taking into account their host stars’ abundances (Fe, Mg, Si, S). We employ a disc evolution model which includes the growth, drift, evaporation and recondensation of pebbles to compute the pebble iron mass fraction. The recondensation of outward-drifting iron vapour near the iron evaporation front is the key mechanism that facilitates an increase in the pebble iron mass fraction. We also simulate the growth of planetary seeds around the iron evaporation front using a planet formation model which includes pebble accretion and planet migration, and compute the final composition of the planets. Our simulations are able to reproduce the observed iron compositions of the super-Mercuries provided that all the iron in the disc are locked in pure Fe grains and that the disc viscosity is low. The combined effects of slow orbital migration of planets and long retention time of iron vapour in low-viscosity discs makes it easier to form iron-rich planets. Furthermore, we find that decreasing the stellar Mg/Si ratio results in an increase in the iron mass fraction of the planet due to a reduction in the abundance of Mg2SiO4, which has a very similar condensation temperature as iron, in the disc. Our results thus imply that super-Mercuries are more likely to form around stars with low Mg/Si, in agreement with observational data.

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J. Mah and B. Bitsch
Wed, 22 Mar 23
5/68

Comments: 9 pages, 6 figures, accepted for publication in A&A

Calibration of the convective parameters in stellar pulsation hydrocodes [SSA]

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http://arxiv.org/abs/2303.12049


Despite the appearance of two- and three-dimensional models thanks to the rapid growth of computing performance, numerical hydrocodes used to model radial stellar pulsations still apply a one-dimensional stellar envelope model without any realistic atmosphere, in which a significant improvement was the inclusion of turbulent convection. However, turbulent convection is an inherently multi-dimensional physical process in the vicinity of the ionization zones that generate pulsation. The description of these processes in one dimension can only be approximated based on simplified theoretical considerations involving several undetermined dimensionless parameters.
In this work, we confront two one-dimensional numerical codes, namely the Budapest-Florida code (BpF) and the MESA Radial Stellar Pulsations module (RSP), with radial velocity observations of several non-modulated RRab stars of the M3 globular cluster and specified the undetermined convective parameters by the measured data for both codes independently.
Our determination shows that some of the parameters depend on the effective temperature, which dependence is established for the first time in this work, and we also found some degeneracy between the parameters. This procedure gives as by-product suggestions for parameters of the publicly available RSP code extensively used recently by researchers through the MESA package.
This work is part of the preparatory work to establish a theoretical framework required to make progress based on the results of one-dimensional models to couple them with multi-dimensional ones for further detailed analysis of physical processes.

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G. Kovács, R. Szabó and J. Nuspl
Wed, 22 Mar 23
8/68

Comments: Accepted in MNRAS, 19 pages, 14 figures, for associated mp4 video see this https URL

Machine Learning the Tip of the Red Giant Branch [GA]

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http://arxiv.org/abs/2303.12069


A novel method for investigating the sensitivity of the tip of the red giant branch (TRGB) I band magnitude $M_I$ to stellar input physics is presented. We compute a grid of $\sim$125,000 theoretical stellar models with varying mass, initial helium abundance, and initial metallicity, and train a machine learning emulator to predict $M_I$ as a function of these parameters. First, our emulator can be used to theoretically predict $M_I$ in a given galaxy using Monte Carlo sampling. As an example, we predict $M_I = -3.84^{+0.14}{-0.12}$ in the Large Magellanic Cloud. Second, our emulator enables a direct comparison of theoretical predictions for $M_I$ with empirical calibrations to constrain stellar modeling parameters using Bayesian Markov Chain Monte Carlo methods. We demonstrate this by using empirical TRGB calibrations to obtain new independent measurements of the metallicity in three galaxies. We find $Z=0.0117^{+0.0083}{-0.0055}$ in the Large Magellanic Cloud, $Z=0.0077^{+0.0074}{-0.0038}$ in NGC 4258, and $Z=0.0111^{+0.0083}{-00.0056}$ in $\omega$-Centauri, consistent with other measurements. Other potential applications of our methodology are discussed.

Read this paper on arXiv…

M. Dennis and J. Sakstein
Wed, 22 Mar 23
11/68

Comments: 9 pages, 6 figures

HD 42477: coupled r modes, g modes and a p mode in an A0Vnne star [SSA]

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http://arxiv.org/abs/2303.11358


Several studies have shown that a number of stars pulsating in p modes lie between the $\beta$ Cep and $\delta$ Sct instability strips in the Hertzsprung-Russell (HR) Diagram. At present, there is no certain understanding of how p~modes can be excited in this $T_{\rm eff}$ range. The goal of this work is to disprove the conjecture that all stars pulsating in p modes and lying in this $T_{\rm eff}$ range are the result of incorrect measurements of $T_{\rm eff}$, contamination, or the presence of unseen cooler companions lying in the $\delta$ Sct instability strip (given the high binary fraction of stars in this region of the HR Diagram). Using TESS data, we show that the A0Vnne star HD 42477 has a single p mode coupled to several r modes and/or g modes. We rule out a contaminating background star with a pixel-by-pixel examination, and we essentially rule out the possibility of a companion $\delta$ Sct star in a binary. We model the pulsations in HD 42477 and suggest that the g modes are excited by overstable convective core modes. We also conjecture that the single p mode is driven by coupling with the g modes, or that the oblateness of this rapidly-rotating star permits driving by He II ionization in the equatorial region.

Read this paper on arXiv…

D. Kurtz, R. Jayaraman, P. Sowicka, et. al.
Wed, 22 Mar 23
12/68

Comments: 11 pages, 6 figures, 2 tables, accepted to MNRAS

Star-Crossed Lovers DI Tau A and B: Orbit Characterization and Physical Properties Determination [SSA]

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http://arxiv.org/abs/2303.11347


The stellar companion to the weak-line T Tauri star DI Tau A was first discovered by the lunar occultation technique in 1989 and was subsequently confirmed by a speckle imaging observation in 1991. It has not been detected since, despite being targeted by five different studies that used a variety of methods and spanned more than 20 years. Here, we report the serendipitous rediscovery of DI Tau B during our Young Exoplanets Spectroscopic Survey (YESS). Using radial velocity data from YESS spanning 17 years, new adaptive optics observations from Keck II, and a variety of other data from the literature, we derive a preliminary orbital solution for the system that effectively explains the detection and (almost all of the) non-detection history of DI Tau B. We estimate the dynamical masses of both components, finding that the large mass difference (q $\sim$0.17) and long orbital period ($\gtrsim$35 years) make DI Tau system a noteworthy and valuable addition to studies of stellar evolution and pre-main-sequence models. With a long orbital period and a small flux ratio (f2/f1) between DI Tau A and B, additional measurements are needed for a better comparison between these observational results and pre-main-sequence models. Finally, we report an average surface magnetic field strength ($\bar B$) for DI Tau A, of $\sim$0.55 kG, which is unusually low in the context of young active stars.

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S. Tang, A. Stahl, L. Prato, et. al.
Wed, 22 Mar 23
28/68

Comments: 21 pages, 10 figures. Accepted to ApJ

New evidence for the precession of tilted disk in SDSS J081256.85+191157.8 [SSA]

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http://arxiv.org/abs/2303.11847


Super-orbital signals and negative superhumps are thought to be related to the reverse precession of the nodal line in a tilted disk, but the evidence is lacking. Our results provide new evidence for the precession of the tilted disk. Based on the TESS and K2 photometry, we investigate the super-orbital signals, negative superhumps, positive superhumps, and eclipse characteristics of the long-period eclipsing cataclysmic variable star SDSS J0812. We find super-orbital signals, negative superhumps, and positive superhumps with periods of 3.0451(5) d, 0.152047(2) d, and 0.174686(7) d, respectively, in the K2 photometry, but all disappear in the TESS photometry, where the positive superhumps are present only in the first half of the same campaign, confirming that none of them is permanently present in SDSS J0812. In addition, we find for the first time a cyclic variation of the O-C of minima, eclipse depth, and negative superhumps amplitudes for 3.045(8) d, 3.040(6) d, and 3.053(8) d in SDSS J0812, respectively, and all reach the maximum at ~ 0.75 precession phases of the tilted disk, which provides new evidence for the precession of the tilted disk. We suggest that the O-C and eclipse depth variations may come from a shift of the brightness center of the precession tilted disk. Our first finding on the periodic variation of negative superhumps amplitude with the super-orbital signals is significant evidence that the origin of negative superhumps is related to the precession of the tilted disk.

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Q. Sun, S. Qian, L. Zhu, et. al.
Wed, 22 Mar 23
38/68

Comments: 21 pages, 16 figures

A Critique of the Spite Plateau, and the Astration of Primordial Lithium [SSA]

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http://arxiv.org/abs/2303.11497


We investigate the distribution of the lithium abundances, A(Li), of metal-poor dwarf and subgiant stars within the limits 5500 K < Teff < 6700 K, -6.0 < [Fe/H] < -1.5, and logg > ~3.5 (a superset of parameters first adopted by Spite and Spite), using literature data for some 200 stars. We address the problem of the several methods that yield Teff differences up to 350 K, and hence uncertainties of 0.3 dex in [Fe/H] and A(Li), by anchoring Teff to the Infrared Flux Method. We seek to understand the behaviour of A(Li) as a function of [Fe/H] — small dispersion at highest [Fe/H], meltdown'' at intermediate values (i.e. large spread in Li below the Spite Plateau), and extreme variations at lowest [Fe/H]. Decreasing A(Li) is accompanied by increasing dispersion. Insofar as [Fe/H] increases as the universe ages, the behavior of A(Li) reflects chaotic star formation involving destruction of primordial Li, which settles to the classic Spite Plateau, with A(Li) ~2.3, by the time the Galactic halo reaches [Fe/H] ~ -3.0. We consider three phases: (1) first star formation in C-rich environments ([C/Fe] &gt; 2.3), with depleted Li; (2) silicates-dominated star formation and destruction of primordial Li during pre-main-sequence evolution; and (3) materials from these two phases co-existing and coalescing to form C-rich stars with A(Li) below the Spite Plateau, leading to a toy model with the potential to explain themeltdown”. We comment on the results of Mucciarelli et al. on the Lower RGB, and the suggestion of Aguado et al. favouring a lower primordial lithium abundance than generally accepted.

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J. Norris, D. Yong, A. Frebel, et. al.
Wed, 22 Mar 23
50/68

Comments: MNRAS in press (see source file for full versions of long tables)

On an Early – Post-AGB Instability [SSA]

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http://arxiv.org/abs/2303.11374


Dynamical stellar-evolution modeling through the AGB phase reveals that radial pulsations with very fast-growing amplitudes develop if the luminosity to mass ratio of stars with tenuous envelopes exceeds a critical limit. An instability going nonlinear already after a few pulsation cycles might qualify as a source of the superwind – postulated to shed a substantial part of a star’s envelope over a very short time – of hitherto persistently mysterious nature.

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A. Gautschy
Wed, 22 Mar 23
59/68

Comments: 15 pages, 12 figures

Short-lived radioisotope enrichment in star-forming regions from stellar winds and supernovae [EPA]

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http://arxiv.org/abs/2303.11393


The abundance of the short-lived radioisotopes 26-Al and 60-Fe in the early Solar system is usually explained by the Sun either forming from pre-enriched material, or the Sun’s protosolar disc being polluted by a nearby supernova explosion from a massive star. Both hypotheses suffer from significant drawbacks: the former does not account for the dynamical evolution of star-forming regions, while in the latter the time for massive stars to explode as supernovae can be similar to, or even longer than, the lifetime of protoplanetary discs. In this paper, we extend the disc enrichment scenario to include the contribution of 26-Al from the winds of massive stars before they explode as supernovae. We use N-body simulations and a post-processing analysis to calculate the amount of enrichment in each disc, and we vary the stellar density of the star-forming regions. We find that stellar winds contribute to disc enrichment to such an extent that the Solar system’s 26-Al/60-Fe ratio is reproduced in up to 50 per cent of discs in dense (rho = 1000Msun pc^-3) star-forming regions. When winds are a significant contributor to the SLR enrichment, we find that Solar system levels of enrichment can occur much earlier (before 2.5 Myr) than when enrichment occurs from supernovae, which start to explode at later ages (>4 Myr). We find that Solar system levels of enrichment all but disappear in low-density star-forming regions (rho < 10Msun pc^-3), implying that the Solar system must have formed in a dense, populous star-forming region if 26-Al and 60-Fe were delivered directly to the protosolar disc from massive-star winds and supernovae.

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R. Parker, T. Lichtenberg, M. Patel, et. al.
Wed, 22 Mar 23
62/68

Comments: 16 pages, 10 figures, 1 appendix with 3 further figures, accepted for publication in MNRAS

What governs the spin distribution of very young < 1 Myr low mass stars [SSA]

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http://arxiv.org/abs/2303.11672


We compute the evolution and rotational periods of young stars, using the MESA code, starting from a stellar seed, and take protostellar accretion, stellar winds, and the magnetic star-disk interaction into account. Furthermore, we add a certain fraction of the energy of accreted material into the stellar interior as additional heat and combine the resulting effects on stellar evolution with the stellar spin model. For different combinations of parameters, stellar periods at an age of 1~Myr range between 0.6~days and 12.9~days. Thus, during the relatively short time period of 1~Myr, a significant amount of stellar angular momentum can already be removed by the interaction between the star and its accretion disk. The amount of additional heat added into the stellar interior, the accretion history, and the presence of disk and stellar winds have the strongest impact on the stellar spin evolution during the first million years. The slowest stellar rotations result from a combination of strong magnetic fields, a large amount of additional heat, and effective winds. The fastest rotators combine weak magnetic fields and ineffective winds or result from a small amount of additional heat added to the star. Scenarios that could lead to such configurations are discussed. Different initial rotation periods of the stellar seed, on the other hand, quickly converges and do not affect the stellar period at all. Our model matches up to 90\% of the observed rotation periods in six young ($\lesssim 3$~Myr) clusters. Based on these intriguing results, we motivate to combine our model with a hydrodynamic disk evolution code to self-consistently include several important aspects such as episodic accretion events, magnetic disk winds, internal, and external photo-evaporation. (Shortened)

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L. Gehrig and E. Vorobyov
Wed, 22 Mar 23
63/68

Comments: 17 pages, 15 figures, accepted for publication in A&A

Quiet Sun flux rope formation via incomplete Taylor relaxation [SSA]

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http://arxiv.org/abs/2303.11738


Low-altitude twisted magnetic fields may be relevant to atmospheric heating in the quiet Sun, but the exact role, topology, and formation of these twisted fields remains to be studied. We investigate the formation and evolution of a preflare flux rope in a stratified, 3D MHD simulation. One puzzle is that this modelled flux rope does not form by the usual mechanisms at work in larger flares such as flux emergence, flux cancellation, or tether-cutting. Using Lagrangian markers to trace representative field lines, we follow the spatiotemporal evolution of the flux rope. We isolate flux bundles associated with reconnecting field line pairs by focusing on thin current sheets within the flux system. We also analyze the time-varying distribution of the force-free parameter as the rope relaxes. Lastly, we compare different seeding methods for magnetic fields and discuss their relevance. We show that the modeled flux rope is gradually built from coalescing, current-carrying flux tubes. This occurs through a series of component reconnections that are driven by flows in the underlying convection zone. These reconnections lead to an inverse cascade of helicity from small to larger scales. We also find that the system attempts to relax toward a linear force-free field, but that the convective drivers and eventual nanoflare prevent full relaxation. Using a self-consistently driven simulation of a nanoflare event, we show for the first time an inverse helicity cascade tending toward a Taylor relaxation in the Sun’s corona, resulting in a well-ordered flux rope that later reconnects with surrounding fields. This provides clues toward understanding the buildup of nanoflare events in the quiet Sun through incomplete Taylor relaxations when no flux emergence or cancellation is observed.

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R. Robinson, G. Aulanier and M. Carlsson
Wed, 22 Mar 23
65/68

Comments: N/A

Modeling CME encounters at Parker Solar Probe with OSPREI: Dependence on photospheric and coronal conditions [SSA]

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http://arxiv.org/abs/2303.10793


Context: Coronal mass ejections (CMEs) are eruptions of plasma from the Sun that travel through interplanetary space and may encounter Earth. CMEs often enclose a magnetic flux rope (MFR), the orientation of which largely determines the CME’s geoeffectiveness. Current operational CME models do not model MFRs, but a number of research ones do, including the Open Solar Physics Rapid Ensemble Information (OSPREI) model. Aims: We report the sensitivity of OSPREI to a range of user-selected photospheric and coronal conditions. Methods: We model four separate CMEs observed in situ by Parker Solar Probe (PSP). We vary the input photospheric conditions using four input magnetograms (HMI Synchronic, HMI Synoptic, GONG Synoptic Zero-Point Corrected, and GONG ADAPT). To vary the coronal field reconstruction, we employ the Potential-Field Source-Surface (PFSS) model and we vary its source-surface height in the range 1.5–3.0 R${\odot}$ with 0.1 R${\odot}$ increments. Results: We find that both the input magnetogram and PFSS source surface often affect the evolution of the CME as it propagates through the Sun’s corona into interplanetary space, and therefore the accuracy of the MFR prediction compared to in-situ data at PSP. There is no obvious best combination of input magnetogram and PFSS source surface height. Conclusions: The OSPREI model is moderately sensitive to the input photospheric and coronal conditions. Based on where the source region of the CME is located on the Sun, there may be best practices when selecting an input magnetogram to use.

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V. Ledvina, E. Palmerio, C. Kay, et. al.
Tue, 21 Mar 23
1/68

Comments: 19 pages, 10 figures, 1 table, accepted for publication in Astronomy & Astrophysics

Optical characteristics and capabilities of the successive versions of Meudon spectroheliograph (1908-2023) [IMA]

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http://arxiv.org/abs/2303.10952


The spectroheliograph is a spectroscopic instrument designed to produce monochromatic images of the photosphere (the visible layer) and the chromosphere of the Sun. It was invented at the same time (1892), but independently, by Hale in the USA and Deslandres in France and was dedicated to long-term surveys of the solar cycles. For that purpose, systematic observations of the CaII K and H$\alpha$ lines started in Meudon observatory in 1908 and continue today, so that a huge collection of more than 100000 spectroheliograms, spanning 115 years of solar activity, was recorded. We present in this paper the optical characteristics and the capabilities of the successive versions of the instrument, from 1908 to now.

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J. Malherbe
Tue, 21 Mar 23
3/68

Comments: N/A

Rainy downdrafts in abyssal atmospheres [EPA]

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http://arxiv.org/abs/2303.10604


Results from Juno’s microwave radiometer indicate non-uniform mixing of ammonia vapor in Jupiter’s atmosphere down to tens of bars, far beneath the cloud level. Helioseismic observations suggest solar convection may require narrow, concentrated downdrafts called entropy rain to accommodate the Sun’s luminosity. Both observations suggest some mechanism of non-local convective transport. We seek to predict the depth that a concentrated density anomaly can reach before efficiently mixing with its environment in bottomless atmospheres. We modify classic self-similar analytical models of entraining thermals to account for the compressibility of an abyssal atmosphere. We compare these models to the output of high resolution three dimensional fluid dynamical simulations to more accurately model the chaotic influence of turbulence. We find that localized density anomalies propagate down to ~3-8 times their initial size without substantially mixing with their environment. Our analytic model accurately predicts the initial flow, but the self-similarity assumption breaks down after the flow becomes unstable at a characteristic penetration depth. In the context of Jupiter, our findings suggest that precipitation concentrated into localized downdrafts of size ~20km can coherently penetrate to on the order of a hundred kilometers (tens of bars) beneath its initial vaporization level without mixing with its environment. This finding is consistent with expected convective storm length-scales, and Juno MWR measurements of ammonia depletion. Compositional gradients of volatiles beneath their cloud levels may be common on stormy giant planets. In the context of the Sun, we find that turbulent downdrafts in abyssal atmospheres cannot maintain their coherence through the Sun’s convective layer, a potential challenge for the entropy rain hypothesis.

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S. Markham, T. Guillot and C. Li
Tue, 21 Mar 23
11/68

Comments: 20 pages, 16 figures. Accepted by A&A

HIP 67506 C: MagAO-X Confirmation of a New Low-Mass Stellar Companion to HIP 67506 A [SSA]

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http://arxiv.org/abs/2303.10200


We report the confirmation of HIP 67506 C, a new stellar companion to HIP 67506 A. We previously reported a candidate signal at 2$\lambda$/D (240~mas) in L$^{\prime}$ in MagAO/Clio imaging using the binary differential imaging technique. Several additional indirect signals showed that the candidate signal merited follow-up: significant astrometric acceleration in Gaia DR3, Hipparcos-Gaia proper motion anomaly, and overluminosity compared to single main sequence stars. We confirmed the companion, HIP 67506 C, at 0.1″ with MagAO-X in April, 2022. We characterized HIP 67506 C MagAO-X photometry and astrometry, and estimated spectral type K7-M2; we also re-evaluated HIP 67506 A in light of the close companion. Additionally we show that a previously identified 9″ companion, HIP 67506 B, is a much further distant unassociated background star. We also discuss the utility of indirect signposts in identifying small inner working angle candidate companions.

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L. Pearce, J. Males, S. Haffert, et. al.
Tue, 21 Mar 23
12/68

Comments: 10 pages, 9 figures, 4 tables, accepted to MNRAS

Origin of magnetism in early-type stars [SSA]

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http://arxiv.org/abs/2303.10707


According to our understanding of stellar evolution, early-type stars have radiative envelopes and convective cores due to a steep temperature gradient produced by the CNO cycle. Some of these stars (mainly, the subclasses Ap and Bp) have strong magnetic fields, enough to be directly observed using the Zeeman effect. Here, we present 3D magnetohydrodynamic simulations of an $2 ~M_{\odot}$ A-type star using the star-in-a-box model. Our goal is to explore if the modeled star is able to maintain a magnetic field as strong as the observed ones, via a dynamo driven by its convective core, or via maintaining a stable fossil field configuration coming from its early evolutionary stages, using different rotation rates. We created two models, a partially radiative and a fully radiative one, which are determined by the value of the heat conductivity. Our model is able to explore both scenarios, including convection-driven dynamos.

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J. Hidalgo, P. Käpylä, C. Ortiz-Rodríguez, et. al.
Tue, 21 Mar 23
14/68

Comments: Conference proceeding (Bolet\’in de la Asociaci\’on Argentina de Astronom\’ia), 3 pages, 3 figures

On excess entropy and latent heat in crystallizing white dwarfs [SSA]

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http://arxiv.org/abs/2303.11311


Based on the linear mixing approach, we calculate the latent heat for crystallizing fully-ionized $^{12}$C/$^{16}$O and $^{16}$O/$^{20}$Ne mixtures in white dwarf (WD) cores for two different parametrizations of the corrections to the linear-mixing energies and with account of ion quantum effects. We report noticeable composition-dependent deviations of the excess entropy in both directions from the standard value of 0.77 per ion. Within the same framework, we evaluate the excess entropy and released or absorbed heat accompanying the exsolution process in solidified WD layers. The inclusion of this effect is shown to be important for reliable interpretation of WD cooling data. We also analyze the latent heat of crystallizing eutectic $^{12}$C/$^{22}$Ne mixture, where we find a qualitative dependence of both the phase diagram and the latent heat behaviour on ion quantum effects. This may be important for the model with $^{22}$Ne distillation in cooling C/O/$^{22}$Ne WD proposed as a solution for the ultramassive WD multi-Gyr cooling anomaly. Astrophysical implications of our findings for crystallizing WD are discussed.

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D. Baiko
Tue, 21 Mar 23
15/68

Comments: 5 pages, 2 figures. Letter to MNRAS, in press

Assessing inner boundary conditions for global coronal modeling of solar maxima [SSA]

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http://arxiv.org/abs/2303.10410


Computational Fluid Dynamics (CFD)-based global solar coronal simulations are slowly making their way into the space weather modeling toolchains to replace the semi-empirical methods such as the Wang-Sheeley-Arge (WSA) model. However, since they are based on CFD, if the assumptions in them are too strong, these codes might experience issues with convergence and unphysical solutions. Particularly the magnetograms corresponding to solar maxima can pose problems as they contain active regions with strong magnetic fields, resulting in large gradients. Combined with the approximate way in which the inner boundary is often treated, this can lead to non-physical features or even a complete divergence of the simulation in these cases. Here, we show some of the possible approaches to handle this inner boundary in our global coronal model COolfluid COrona uNstrUcTured (COCONUT) in a way that improves both convergence and accuracy. Since we know that prescribing the photospheric magnetic field for a region that represents the lower corona is not entirely physical, first, we look at the ways in which we can adjust the input magnetograms to remove the highest magnitudes and gradients. Secondly, since in the default setup we also assume a constant density, here we experiment with changing these values locally and globally to see the effect on the results. We conclude, through comparison with observations and convergence analysis, that modifying the density locally in active regions is the best way to improve the performance both in terms of convergence and physical accuracy from the tested approaches.

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M. Brchnelova, B. Kuźma, F. Zhang, et. al.
Tue, 21 Mar 23
16/68

Comments: 11 pages, 4 figures

Slow solar wind sources. High-resolution observations with a quadrature view [SSA]

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http://arxiv.org/abs/2303.11001


The origin of the slow solar wind is still an open issue. One possibility that has been suggested is that upflows at the edge of an active region can contribute to the slow solar wind.
We aim to explain how the plasma upflows are generated, which mechanisms are responsible for them, and what the upflow region topology looks like.
We investigated an upflow region using imaging data with the unprecedented temporal (3s) and spatial (2 pixels = 236km) resolution that were obtained on 30 March 2022 with the 174{\AA} of the Extreme-Ultraviolet Imager (EUI)/High Resolution Imager (HRI) on board Solar Orbiter. During this time, the EUI and Earth-orbiting satellites (Solar Dynamics Observatory, Hinode, and the Interface Region Imaging Spectrograph, IRIS) were located in quadrature (92 degrees), which provides a stereoscopic view with high resolution. We used the Hinode/EIS (Fe XII) spectroscopic data to find coronal upflow regions in the active region. The IRIS slit-jaw imager provides a high-resolution view of the transition region and chromosphere.
For the first time, we have data that provide a quadrature view of a coronal upflow region with high spatial resolution. We found extended loops rooted in a coronal upflow region. Plasma upflows at the footpoints of extended loops determined spectroscopically through the Doppler shift are similar to the apparent upward motions seen through imaging in quadrature. The dynamics of small-scale structures in the upflow region can be used to identify two mechanisms of the plasma upflow: Mechanism I is reconnection of the hot coronal loops with open magnetic field lines in the solar corona, and mechanism II is reconnection of the small chromospheric loops with open magnetic field lines in the chromosphere or transition region. We identified the locations in which mechanisms I and II work.

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K. Barczynski, L. Harra, C. Schwanitz, et. al.
Tue, 21 Mar 23
25/68

Comments: 10 pages, 6 figures, accepted for publication in A&A; manuscript is a part of Astronomy & Astrophysics special issue: Solar Orbiter First Results (Nominal Mission Phase)

In search for infalling clumps in molecular clouds — A catalogue of CO blue-profiles [GA]

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http://arxiv.org/abs/2303.10982


We have started a systematic survey of molecular clumps with infall motions to study the very early phase of star formation. Our first step is to utilize the data products by MWISP to make an unbiased survey for blue asymmetric line profiles of CO isotopical molecules. Within a total area of $\sim$ 2400 square degrees nearby the Galactic plane, we have found 3533 candidates showing blue-profiles, in which 3329 are selected from the $^{12}$CO&$^{13}$CO pair and 204 are from the $^{13}$CO&C$^{18}$O pair. Exploration of the parametric spaces suggests our samples are in the cold phase with relatively high column densities ready for star formation. Analysis of the spatial distribution of our samples suggests that they exist virtually in all major components of the Galaxy. The vertical distribution suggest that the sources are located mainly in the thick disk of $\sim$ 85 parsec, but still a small part are located far beyond Galactic midplane. Our follow-up observation indicates that these candidates are a good sample to start a search for infall motions, and to study the condition of very early phase of star formation.

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Z. Jiang, S. Zhang, Z. Chen, et. al.
Tue, 21 Mar 23
26/68

Comments: N/A

Nonlinear Damping and Field-aligned Flows of Propagating Shear Alfvén Waves with Braginskii Viscosity [SSA]

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http://arxiv.org/abs/2303.11128


Braginskii MHD provides a more accurate description of many plasma environments than classical MHD since it actively treats the stress tensor using a closure derived from physical principles. Stress tensor effects nonetheless remain relatively unexplored for solar MHD phenomena, especially in nonlinear regimes. This paper analytically examines nonlinear damping and longitudinal flows of propagating shear Alfv\’en waves. Most previous studies of MHD waves in Braginskii MHD considered the strict linear limit of vanishing wave perturbations. We show that those former linear results only apply to Alfv\’en wave amplitudes in the corona that are so small as to be of little interest, typically a wave energy less than $10^{-11}$ times the energy of the background magnetic field. For observed wave amplitudes, the Braginskii viscous dissipation of coronal Alfv\’en waves is nonlinear and a factor around $10^9$ stronger than predicted by the linear theory. Furthermore, the dominant damping occurs through the parallel viscosity coefficient $\eta_0$, rather than the perpendicular viscosity coefficient $\eta_2$ in the linearized solution. This paper develops the nonlinear theory, showing that the wave energy density decays with an envelope $(1+z/L_d)^{-1}$. The damping length $L_d$ exhibits an optimal damping solution, beyond which greater viscosity leads to lower dissipation as the viscous forces self-organise the longitudinal flow to suppress damping. Although the nonlinear damping greatly exceeds the linear damping, it remains negligible for many coronal applications.

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A. Russell
Tue, 21 Mar 23
29/68

Comments: Accepted for publication in ApJ