Tag Archives: Solar and Stellar Astrophysics

Production rates of dark photons and $Z'$ in the Sun and stellar cooling bounds [CL]

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http://arxiv.org/abs/2304.12907


Light weakly interacting particles could be copiously produced in the Sun which, as a well-understood star, could provide severe constraints on such new physics. In this work, we calculate the solar production rates of light gauge bosons (e.g. dark photon) arising from various $U(1)$ extensions of the standard model. It is known that the dark photon production rate is suppressed by the dark photon mass if it is well below the plasmon mass of the medium. We show that for more general $U(1)$ gauge bosons, this suppression is absent if the couplings are not in alignment with those of the photon. We investigate a few frequently discussed $U(1)$ models including $B-L$, $L_{\mu}-L_{\tau}$, and $L_{e}-L_{\mu(\tau)}$, and derive the stellar cooling bounds for these models.

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S. Li and X. Xu
Wed, 26 Apr 23
22/62

Comments: 22 pages, 4 figures. Comments are welcome

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

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http://arxiv.org/abs/2304.12355


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

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

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

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

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http://arxiv.org/abs/2304.12942


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

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

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

SN 2020udy: a SN Iax with strict limits on interaction consistent with a helium-star companion [HEAP]

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http://arxiv.org/abs/2304.12361


Early observations of transient explosions can provide vital clues to their progenitor origins. In this paper we present the nearby Type Iax (02cx-like) supernova (SN), SN 2020udy that was discovered within hours ($\sim$7 hr) of estimated first light. An extensive dataset of ultra-violet, optical, and near-infrared observations was obtained, covering out to $\sim$150 d after explosion. SN 2020udy peaked at -17.86$\pm$0.43 mag in the r band and evolved similarly to other ‘luminous’ SNe Iax, such as SNe 2005hk and 2012Z. Its well-sampled early light curve allows strict limits on companion interaction to be placed. Main-sequence companion stars with masses of 2 and 6 M$_\odot$ are ruled out at all viewing angles, while a helium-star companion is allowed from a narrow range of angles (140-180$^\circ$ away from the companion). The spectra and light curves of SN2020udy are in good agreement with those of the ‘N5def’ deflagration model of a near Chandrasekhar-mass carbon-oxygen white dwarf. However, as has been seen in previous studies of similar luminosity events, SN 2020udy evolves slower than the model. Broad-band linear polarisation measurements taken at and after peak are consistent with no polarisation, in agreement with the predictions of the companion-star configuration from the early light curve measurements. The host galaxy environment is low metallicity and is consistent with a young stellar population. Overall, we find the most plausible explosion scenario to be the incomplete disruption of a CO white dwarf near the Chandrasekhar-mass limit, with a helium-star companion.

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K. Maguire, M. Magee, G. Leloudas, et. al.
Wed, 26 Apr 23
36/62

Comments: 18 pages, 14 figures, submitted to MNRAS

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

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http://arxiv.org/abs/2304.12938


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

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

Comments: N/A

Discovery of extraordinary X-ray emission from magnetospheric interaction in the unique binary stellar system $ε$ Lupi [HEAP]

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http://arxiv.org/abs/2304.12882


We report detailed X-ray observations of the unique binary system $\epsilon$ Lupi, the only known short-period binary consisting of two magnetic early-type stars. The components have comparably strong, but anti-aligned magnetic fields. The orbital and magnetic properties of the system imply that the magnetospheres overlap at all orbital phases, suggesting the possibility of variable inter-star magnetospheric interaction due to the non-negligible eccentricity of the orbit. To investigate this effect, we observed the X-ray emission from $\epsilon$ Lupi both near and away from periastron passage, using the Neutron Star Interior Composition Explorer mission (NICER) X-ray Telescope. We find that the system produces excess X-ray emission at the periastron phase, suggesting the presence of variable inter-star magnetospheric interaction. We also discover that the enhancement at periastron is confined to a very narrow orbital phase range ($\approx 5\%$ of the orbital period), but the X-ray properties close to periastron phase are similar to those observed away from periastron. From these observations, we infer that the underlying cause is magnetic reconnection heating the stellar wind plasma, rather than shocks produced by wind-wind collision. Finally, by comparing the behavior of $\epsilon$ Lupi with that observed for cooler magnetic binary systems, we propose that elevated X-ray flux at periastron phase is likely a general characteristic of interacting magnetospheres irrespective of the spectral types of the constituent stars.

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B. Das, V. Petit, Y. Nazé, et. al.
Wed, 26 Apr 23
44/62

Comments: Accepted for publication in MNRAS (20 pages, 17 figures)

Enabling Exoplanet Demographics Studies with Standardized Exoplanet Survey Meta-Data [IMA]

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http://arxiv.org/abs/2304.12442


Goal 1 of the National Academies of Science, Engineering and Mathematics Exoplanet Science Strategy is “to understand the formation and evolution of planetary systems as products of the process of star formation, and characterize and explain the diversity of planetary system architectures, planetary compositions, and planetary environments produced by these processes”, with the finding that “Current knowledge of the demographics and characteristics of planets and their systems is substantially incomplete.” One significant roadblock to our ongoing efforts to improve our demographics analyses is the lack of comprehensive meta-data accompanying published exoplanet surveys. The Exoplanet Program Analysis Group (ExoPAG) Science Interest Group 2: Exoplanet Demographics has prepared this document to provide guidance to survey architects, authors, referees and funding agencies as to the most valuable such data products for five different exoplanet detection techniques – transit, radial velocity, direct imaging, microlensing and astrometry. We find that making these additional data easily available would greatly enhance the community’s ability to perform robust, reproducible demographics analyses, and make progress on achieving the most important goals identified by the exoplanet and wider astronomical community.

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P. Group, 2. Demographics, J. Christiansen, et. al.
Wed, 26 Apr 23
48/62

Comments: 21 pages, final report after community feedback addressed

Bioverse: A Comprehensive Assessment of the Capabilities of Extremely Large Telescopes to Probe Earth-like O$_\mathrm{2}$ Levels in Nearby Transiting Habitable Zone Exoplanets [EPA]

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http://arxiv.org/abs/2304.12490


Molecular oxygen is a strong indicator of life on Earth, and may indicate biological processes on exoplanets too. Recent studies proposed that Earth-like O$\mathrm{2}$ levels might be detectable on nearby exoplanets using high-resolution spectrographs on future extremely large telescopes (ELTs). However, these studies did not consider constraints like relative velocities, planet occurrence rates, and target observability. We expanded on past studies by creating a homogeneous catalog of 286,391 main-sequence stars within 120 pc using Gaia DR3, and used the Bioverse framework to simulate the likelihood of finding nearby transiting Earth analogs. We also simulated a survey of M dwarfs within 20 pc accounting for $\eta{\oplus}$ estimates, transit probabilities, relative velocities, and target observability to determine how long ELTs and theoretical 50-100 meter ground-based telescopes need to observe to probe for Earth-like O$\mathrm{2}$ levels with an $R=100,000$ spectrograph. This would only be possible within 50 years for up to $\sim$21% of nearby M dwarf systems if a suitable transiting habitable zone Earth-analog was discovered, assuming signals from every observable partial transit from each ELT can be combined. If so, Earth-like O$\mathrm{2}$ levels could be detectable on TRAPPIST-1 d-g within 16 to 55 years, respectively, and about half that time with an $R=500,000$ spectrograph. These results have important implications for whether ELTs can survey nearby habitable zone Earth analogs for O$_\mathrm{2}$ via transmission spectroscopy. Our work provides the most comprehensive assessment to date of the ground-based capabilities to search for life beyond the solar system.

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K. Hardegree-Ullman, D. Apai, G. Bergsten, et. al.
Wed, 26 Apr 23
54/62

Comments: 30 pages, 14 figures, 8 tables. Revised and resubmitted to AJ after a favorable referee report

The shared evaporation history of three sub-Neptunes spanning the radius-period valley of a Hyades star [EPA]

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http://arxiv.org/abs/2304.12705


We model the evaporation histories of the three planets around K2-136, a K-dwarf in the Hyades open cluster with an age of 700 Myr. The star hosts three transiting planets, with radii of 1.0, 3.0 and 1.5 Earth radii, where the middle planet lies above the radius-period valley and the inner and outer planets are below. We use an XMM-Newton observation to measure the XUV radiation environment of the planets, finding that the X-ray activity of K2-136 is lower than predicted by models but typical of similar Hyades members. We estimate the internal structure of each planet, and model their evaporation histories using a range of structure and atmospheric escape formulations. While the precise X-ray irradiation history of the system may be uncertain, we exploit the fact that the three planets must have shared the same history. We find that the Earth-sized K2-136b is most likely rocky, with any primordial gaseous envelope being lost within a few Myr. The sub-Neptune, K2-136c, has an envelope contributing 1-1.7% of its mass that is stable against evaporation thanks to the high mass of its rocky core, whilst the super-Earth, K2-136d, must have a mass at the upper end of the allowed range in order to retain any of its envelope. Our results are consistent with all three planets beginning as sub-Neptunes that have since been sculpted by atmospheric evaporation to their current states, stripping the envelope from planet b and removing most from planet d whilst preserving planet c above the radius-period valley.

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J. Fernández, P. Wheatley and G. King
Wed, 26 Apr 23
57/62

Comments: Accepted for publication on MNRAS

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

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http://arxiv.org/abs/2304.12974


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

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

Comments: 18 pages, 14 figures

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

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http://arxiv.org/abs/2304.11785


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

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

Comments: 17 pages, 7 figures

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

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http://arxiv.org/abs/2304.11162


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

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

Comments: Accepted for publication in Astronomy and Astrophysics

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

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http://arxiv.org/abs/2304.12156


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

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

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

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

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http://arxiv.org/abs/2304.12028


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

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

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

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

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http://arxiv.org/abs/2304.12037


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

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

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

WASP-131 b with ESPRESSO I: A bloated sub-Saturn on a polar orbit around a differentially rotating solar-type star [EPA]

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http://arxiv.org/abs/2304.12163


In this paper, we present observations of two high-resolution transit datasets obtained with ESPRESSO of the bloated sub-Saturn planet WASP-131~b. We have simultaneous photometric observations with NGTS and EulerCam. In addition, we utilised photometric lightcurves from {\tess}, WASP, EulerCam and TRAPPIST of multiple transits to fit for the planetary parameters and update the ephemeris. We spatially resolve the stellar surface of WASP-131 utilising the Reloaded Rossiter McLaughlin technique to search for centre-to-limb convective variations, stellar differential rotation, and to determine the star-planet obliquity for the first time. We find WASP-131 is misaligned on a nearly retrograde orbit with a projected obliquity of $\lambda = 162.4\substack{+1.3 \ -1.2}^{\circ}$. In addition, we determined a stellar differential rotation shear of $\alpha = 0.61 \pm 0.06$ and disentangled the stellar inclination ($i_* = 40.9\substack{+13.3 \ -8.5}^{\circ}$) from the projected rotational velocity, resulting in an equatorial velocity of $v_{\rm{eq}} = 7.7\substack{+1.5 \ -1.3}$~km s$^{-1}$. In turn, we determined the true 3D obliquity of $\psi = 123.7\substack{+12.8 \ -8.0}^{\circ}$, meaning the planet is on a perpendicular/polar orbit. Therefore, we explored possible mechanisms for the planetary system’s formation and evolution. Finally, we searched for centre-to-limb convective variations where there was a null detection, indicating that centre-to-limb convective variations are not prominent in this star or are hidden within red noise.

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L. Doyle, H. Cegla, D. Anderson, et. al.
Tue, 25 Apr 23
36/72

Comments: 15 Pages, 10 Figures and 4 Tables Accepted for Publication in MNRAS. arXiv admin note: text overlap with arXiv:2207.10127

Rotational spectroscopy of oxirane-\textit{2,2}-$d_2$, $c$-CD$_2$CH$_2$O, and its tentative detection toward IRAS 16293$-$2422~B [GA]

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http://arxiv.org/abs/2304.12045


We prepared a sample of oxirane doubly deuterated at one C atom and studied its rotational spectrum in the laboratory for the first time between 120~GHz and 1094~GHz. Accurate spectroscopic parameters up to eighth order were determined, and the calculated rest frequencies were used to identify $c$-CD$2$CH$_2$O tentatively in the interstellar medium in the Atacama Large Millimeter/submillimeter Array Protostellar Interferometric Line Survey (PILS) of the Class 0 protostellar system IRAS 16293$-$2422. The $c$-CD$_2$CH$_2$O to $c$-C$_2$H$_4$O ratio was estimated to be $\sim$0.054 with $T{\rm rot} = 125$ K. This value translates to a D-to-H ratio of $\sim$0.16 per H atom which is higher by a factor of 4.5 than the $\sim$0.036 per H atom obtained for $c$-C$_2$H$_3$DO. Such increase in the degree of deuteration referenced to one H atom in multiply deuterated isotopologs compared to their singly deuterated variants have been observed commonly in recent years.

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H. Müller, J. Jørgensen, J. Guillemin, et. al.
Tue, 25 Apr 23
38/72

Comments: Journal of Molecular Spectroscopy, in press; Per Jensen special issue. 12 pages here

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

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http://arxiv.org/abs/2304.11802


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

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

Comments: 19 pages, 5 figures

Tidal dissipation in stratified and semi-convective regions of giant planets [EPA]

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http://arxiv.org/abs/2304.11898


We study how stably stratified or semi-convective layers alter the tidal dissipation rates associated with the generation of internal waves in planetary interiors. We consider if these layers could contribute to the high rates of tidal dissipation observed for Jupiter and Saturn in our solar system. We use an idealised global spherical Boussinesq model to study the influence of stable stratification and semi-convective layers on tidal dissipation rates. We carry out analytical and numerical calculations considering realistic tidal forcing and measure how the viscous and thermal dissipation rates depend on the parameters relating to the internal stratification profile. We find that the strongly frequency-dependent tidal dissipation rate is highly dependent on the parameters relating to the stable stratification, with strong resonant peaks that align with the internal modes of the system. The locations and sizes of these resonances depend on the form and parameters of the stratification, which we explore both analytically and numerically. Our results suggest that stable stratification can significantly enhance the tidal dissipation in particular frequency ranges. Analytical calculations in the low frequency regime give us scaling laws for the key parameters, including the tidal quality factor $Q’$ due to internal gravity waves. Stably stratified layers can significantly contribute to tidal dissipation in solar and extrasolar giant planets, and we estimate substantial tidal evolution for hot Neptunes. Further investigation is needed to robustly quantify the significance of the contribution in realistic interior models, and to consider the contribution of inertial waves.

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C. Pontin, A. Barker and R. Hollerbach
Tue, 25 Apr 23
40/72

Comments: 29 pages, 17 figures, accepted for publication in ApJ (13th April 2023)

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

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http://arxiv.org/abs/2304.11307


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

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

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

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

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http://arxiv.org/abs/2304.12197


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

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

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

High-velocity CP2 stars in the Galactic halo [GA]

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http://arxiv.org/abs/2304.11269


Context. The second subclass of chemically peculiar stars, the CP2 stars, are early-type stars exhibiting anomalous abundances with variable line strengths possibly also accompanied by photometric variability that typically belong to the Galactic disk. However, a small fraction of these objects were recently found to be located far from the Galactic plane and are thought to belong to the Galactic halo, which is unexpected for this class of objects. Aims. Our study investigates the halo membership of the proposed halo CP2 star candidates based on their velocities and Galactic orbits, to determine their points of origin. In addition, we searched for further halo CP2 star candidates using an as-yet-unpublished sample of CP stars. Methods. Our analysis relied on the astrometry from the early third \textit{Gaia} data release and radial velocities based on the spectroscopy from LAMOST and SDSS, which was also employed in spectral classification. The light variability of the confirmed CP2 stars in our sample was analyzed using data from the ZTF and ATLAS surveys. Results. After filtering our initial sample using kinematic and spectroscopic criteria, we identified six CP2 stars with kinematical properties consistent with a halo membership. The orbits of these stars are in agreement with an origin in the Galactic disk where they were probably ejected through dynamical interactions or in the binary supernova scenario, making them the first runaway CP2 stars known.

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N. Faltová, M. Prišegen, K. Bernhard, et. al.
Tue, 25 Apr 23
63/72

Comments: 13 pages, 11 figures, accepted for publication in A&A

The GeMS/GSAOI Galactic Globular Cluster Survey (G4CS) II: Characterization of 47 Tuc with Bayesian Statistics [GA]

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http://arxiv.org/abs/2304.11240


We present a photometric analysis of globular cluster 47 Tuc (NGC\,104), using near-IR imaging data from the GeMS/GSAOI Galactic Globular Cluster Survey (G4CS) which is in operation at Gemini-South telescope.~Our survey is designed to obtain AO-assisted deep imaging with near diffraction-limited spatial resolution of the central fields of Milky Way globular clusters.~The G4CS near-IR photometry was combined with an optical photometry catalog obtained from Hubble Space Telescope survey data to produce a high-quality color-magnitude diagram that reaches down to K$s\approx$ 21 Vega mag.~We used the software suite BASE-9, which uses an adaptive Metropolis sampling algorithm to perform a Markov chain Monte Carlo (MCMC) Bayesian analysis, and obtained probability distributions and precise estimates for the age, distance and extinction cluster parameters.~Our best estimate for the age of 47 Tuc is 12.42$^{+0.05}{-0.05}$ $\pm$ 0.08 Gyr, and our true distance modulus estimate is (m$-$M)$0$=13.250$^{+0.003}{-0.003}$ $\pm$ 0.028 mag, in tight agreement with previous studies using Gaia DR2 parallax and detached eclipsing binaries.

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M. Simunovic, T. Puzia, B. Miller, et. al.
Tue, 25 Apr 23
65/72

Comments: 25 pages, 15 figures. Accepted for publication in The Astrophysical Journal

Photometric determination of the mass accretion rates of pre-main-sequence stars. VIII. Recent star formation in NGC 299 [GA]

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http://arxiv.org/abs/2304.12137


We studied the properties of the young stellar populations in the NGC 299 cluster in the Small Magellanic Cloud using observations obtained with the Hubble Space Telescope in the $V, I$, and $H\alpha$ bands. We identified 252 stars with H$\alpha$ excess exceeding 5 $\sigma$ and an equivalent width of the H$\alpha$ emission line of at least 20 \r{A}, indicating that these stars are still undergoing accretion and therefore represent bona fide pre-main-sequence (PMS) objects. For all of them, we derived the mass, age, and mass accretion rate by comparing the observed photometry with theoretical models. We find evidence for the existence of two populations of PMS stars, with median ages of 25 and 50 Myr respectively. The average mass accretion rate for these PMS stars is $\sim 5 \times 10^{-9}$ M$_\odot$ yr$^{-1}$, which is comparable to the values found in other low-metallicity, low-density clusters in the Magellanic Clouds, but is about a factor of three lower than those measured for stars of similar mass and age in denser Magellanic Cloud stellar regions. Our findings support the hypothesis that both the metallicity and density of the forming environment can affect the mass accretion rate and thus the star formation process in a region.
A study of the spatial distribution of both massive stars and (low-mass) PMS objects reveals that the former are clustered near the nominal centre of NGC 299, whereas the PMS stars are rather uniformly distributed over the field. To explore whether the stars formed in an initially more diffuse or compact structure, we studied the cluster’s stellar density profile. We find a core radius $r_c\simeq 0.6$ pc and a tidal radius $r_t\simeq 5.5$ pc, with an implied concentration parameter $c \simeq 1$, suggesting that the cluster could be dispersing into the field.

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M. Vlasblom and G. Marchi
Tue, 25 Apr 23
68/72

Comments: 14 pages, 11 figures, accepted for publication in A&A

Stellar Collisions in the Galactic Center: Massive Stars, Collision Remnants, and Missing Red Giants [GA]

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http://arxiv.org/abs/2304.10569


Like most galaxies, the Milky Way harbors a supermassive black hole (SMBH) at its center, surrounded by a nuclear star cluster. In this dense star cluster, direct collisions can occur between stars before they evolve off the main-sequence. Using a statistical approach, we characterize the outcomes of these stellar collisions within the inner parsec of the Galactic Center (GC). Close to the SMBH, where the velocity dispersion is larger than the escape speed from a Sun-like star, collisions lead to mass loss. We find that the stellar population within $0.01$ pc is halved within about a Gyr because of destructive collisions. Additionally, we predict a diffuse population of peculiar low-mass stars in the GC. These stars have been divested of their outer layers in the inner $0.01$ pc before migrating to larger distances from the SMBH. Between $0.01$ and $0.1$ pc from the SMBH, collisions can result in mergers. Our results suggest that repeated collisions between lower mass stars can produce massive ($\gtrsim 10$ M$_\odot$) stars, and there may be $\sim 100$ of them residing in this region. We provide predictions on the number of G objects, dust and gas enshrouded stellar objects, that may result from main-sequence stellar collisions. Lastly, we comment on uncertainties in our model and possible connections between stellar collisions and the missing red giants in the GC.

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S. Rose, S. Naoz, R. Sari, et. al.
Mon, 24 Apr 23
2/41

Comments: Submitted to ApJ. Comments welcome. 24 pages, 13 figures

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

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http://arxiv.org/abs/2304.10654


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

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

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

The spin-down accretion regime of Galactic ultra-luminous X-ray pulsar Swift J0243.6+6124 [HEAP]

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http://arxiv.org/abs/2304.10815


The relative high fluxes of the Galactic ultra-luminous X-ray pulsar Swift J0243 allow a detailed study of its spin-down regime in quiescence state, for a first time. After the 2017 giant outburst, its spin frequencies show a linear decreasing trend with some variations due to minor outbursts. The linear spin-down rate is $\sim-1.9\times10^{-12}$ Hz/s during the period of lowest luminosity, from which one can infer a dipole field $\sim1.75\times10^{13}$ G. The $\dot{\nu}-L$ relation during the spin-down regime is complex, and the $\dot{\nu}$ is close to 0 when the luminosity reaches both the high end ($L_{38}\sim0.3$) and the lowest value ($L_{38}\sim0.03$). The luminosity of zero-torque is different for the giant outburst and other minor outbursts. It is likely due to different accretion flows for different types of outburst, as evidenced by the differences of the spectra and pulse profiles at a similar luminosity for different types of outburst (giant or not). The pulse profile changes from double peaks in the spin-up state to a single broad peak in the low spin-down regime, indicating the emission beam/region is larger in the low spin-down regime. These results show that accretion is still ongoing in the low spin-down regime for which the neutron star is supposed to be in a propeller state.

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J. Liu, L. Ji and M. Ge
Mon, 24 Apr 23
9/41

Comments: 7 pages, 7 figs, to appear in ApJ, comments welcome

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

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http://arxiv.org/abs/2304.10886


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

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

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

Exploring the stellar surface phenomena of WASP-52 and HAT-P-30 with ESPRESSO [EPA]

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http://arxiv.org/abs/2304.11022


We analyse spectroscopic and photometric transits of the hot Jupiters WASP-52b and HAT-P30b obtained with ESPRESSO, Eulercam and NGTS for both targets, and additional TESS data for HAT-P-30. Our goal is to update the system parameters and refine our knowledge of the host star surfaces. For WASP-52, the companion planet has occulted starspots in the past, and as such our aim was to use the reloaded Rossiter-McLaughlin technique to directly probe its starspot properties. Unfortunately, we find no evidence for starspot occultations in the datasets herein. Additionally, we searched for stellar surface differential rotation (DR) and any centre-to-limb variation (CLV) due to convection, but return a null detection of both. This is unsurprising for WASP-52, given its relatively cool temperature, high magnetic activity (which leads to lower CLV), and projected obliquity near 0 degrees (meaning the transit chord is less likely to cross several stellar latitudes). For HAT-P-30, this result was more surprising given its hotter effective temperature, lower magnetic field, and high projected obliquity (near 70 degrees). To explore the reasons behind the null DR and CLV detection for HAT-P-30, we simulated a variety of scenarios. We find that either the CLV present on HAT-P-30 is below the solar level or the presence of DR prevents a CLV detection given the precision of the data herein. A careful treatment of both DR and CLV is required, especially for systems with high impact factors, due to potential degeneracies between the two. Future observations and/or a sophisticated treatment of the red noise present in the data (likely due to granulation) is required to refine the DR and CLV for these particular systems; such observations would also present another opportunity to try to examine starspots on WASP-52.

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H. Cegla, N. Roguet-Kern, M. Lendl, et. al.
Mon, 24 Apr 23
19/41

Comments: 11 pages main text, 8 figures; accepted for publication in A&A

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

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http://arxiv.org/abs/2304.10670


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

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

Comments: Accepted for publication in ApJ. 16 pages

S-ACF: A selective estimator for the autocorrelation function of irregularly sampled time series [IMA]

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http://arxiv.org/abs/2304.10641


We present a generalised estimator for the autocorrelation function, S-ACF, which is an extended version of the standard estimator of the autocorrelation function (ACF). S-ACF is a versatile definition that can robustly and efficiently extract periodicity and signal shape information from a time series, independent of the time sampling and with minimal assumptions about the underlying process. Calculating the autocorrelation of irregularly sampled time series becomes possible by generalising the lag of the standard estimator of the ACF to a real parameter and introducing the notion of selection and weight functions. We show that the S-ACF reduces to the standard ACF estimator for regularly sampled time series. Using a large number of synthetic time series we demonstrate that the performance of the S-ACF is as good or better than commonly used Gaussian and rectangular kernel estimators, and is comparable to a combination of interpolation and the standard estimator. We apply the S-ACF to astrophysical data by extracting rotation periods for the spotted star KIC 5110407, and compare our results to Gaussian process (GP) regression and Lomb-Scargle (LS) periodograms. We find that the S-ACF periods typically agree better with those from GP regression than from LS periodograms, especially in cases where there is evolution in the signal shape. The S-ACF has a wide range of potential applications and should be useful in quantitative science disciplines where irregularly sampled time series occur. A Python implementation of the S-ACF is available under the MIT license.

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L. Kreutzer, E. Gillen, J. Briegal, et. al.
Mon, 24 Apr 23
28/41

Comments: N/A

Properties of the dense cores and filamentary structures in the Vela C molecular cloud [GA]

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http://arxiv.org/abs/2304.10863


The initial and boundary conditions of the Galactic star formation in molecular clouds are not well understood. In an effort to shed new light on this long-standing problem, we measured properties of dense cores and filamentary structures in the Vela C molecular cloud, observed with Herschel. We applied the getsf extraction method to separate the components of sources and filaments from each other and their backgrounds, before detecting, measuring, and cataloging the structures. The cores and filamentary structures constitute 40% of the total mass of Vela C, most of the material is in the low-density molecular background cloud. We selected 570 reliable cores, of which 149 are the protostellar cores and 421 are the starless cores. Almost 78% of the starless cores were identified with the gravitationally bound prestellar cores. The exponent of the CMF (alpha = 1.35) is identical to that of the Salpeter IMF. We selected 68 filaments with at least one side that appeared not blended with adjacent structures. The filament widths are in the range of 0.15 pc to 0.63 pc, and have a median value of W = 0.3(0.11) pc. The surface densities of filaments are well correlated with their contrasts and linear densities. Within uncertainties of the filament instability criterion, many filaments may well be both supercritical and subcritical. A large fraction of filaments may definitely be considered supercritical, in which are found 94 prestellar cores, 83 protostellar cores, and only 1 unbound starless core. Taking into account the uncertainties, the supercritical filaments contain only prestellar and protostellar cores. Our findings support the idea that there exists a direct relationship between the CMF and IMF and that filaments play a key role in the formation of prestellar cores, which is consistent with the previous Herschel results.

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X. Li, G. Zhang, A. Men’shchikov, et. al.
Mon, 24 Apr 23
30/41

Comments: 15 pages, 12 figures, 3 tables, accepted for publication in A&A

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

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http://arxiv.org/abs/2304.11078


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

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

Comments: N/A

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

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http://arxiv.org/abs/2304.10330


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

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

Comments: MNRAS, in press

Exoplanet Nodal Precession Induced by Rapidly Rotating Stars: Impacts on Transit Probabilities and Biases [EPA]

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http://arxiv.org/abs/2304.09890


For the majority of short period exoplanets transiting massive stars with radiative envelopes, the spin angular momentum of the host star is greater than the planetary orbital angular momentum. In this case, the orbits of the planets will undergo nodal precession, which can significantly impact the probability that the planets transit their parent star. In particular, for some combinations of the spin-orbit angle $\psi$ and the inclination of the stellar spin $i_*$, all such planets will eventually transit at some point over the duration of their precession period. Thus, as the time over which the sky has been monitored for transiting planets increases, the frequency of planets with detectable transits will increase, potentially leading to biased estimates of exoplanet occurrence rates, especially orbiting more massive stars. Furthermore, due to the dependence of the precession period on orbital parameters such as spin-orbit misalignment, the observed distributions of such parameters may also be biased. We derive the transit probability of a given exoplanet in the presence of nodal precession induced by a rapidly spinning host star. We find that the effect of nodal precession has already started to become relevant for some short-period planets, i.e., Hot Jupiters, orbiting massive stars, by increasing transit probabilities by of order a few percent for such systems within the original $Kepler$ field. We additionally derive simple expressions to describe the time evolution of the impact parameter $b$ for applicable systems, which should aid in future investigations of exoplanet nodal precession and spin-orbit alignment.

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A. Stephan and B. Gaudi
Fri, 21 Apr 23
8/60

Comments: 9 pages, 5 figures, accepted for publication in ApJ

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

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http://arxiv.org/abs/2304.09896


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

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

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

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

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http://arxiv.org/abs/2304.10173


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

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

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

The statistical analysis of the dynamical evolution of the open clusters [GA]

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http://arxiv.org/abs/2304.10138


We present the dynamical evolution of ten open clusters which were part of our previous studies. These clusters include both young and intermediate-age open clusters with ages ranging from 25$\pm$19 Myr to 1.78$\pm$0.20 Gyr. The total mass of these clusters ranges from 356.18$\pm$142.90 to 1811.75$\pm$901.03 M${\odot}$. The Galactocentric distances to the clusters are in the range of 8.91$\pm$0.02 to 11.74$\pm$0.18 kpc. The study is based on the ground-based UBVRI data supplemented by the astrometric data from the Gaia archive. We studied the minimum spanning tree of the member stars for these clusters. The mass segregation in these clusters was quantified by mass segregation ratios calculated from the mean edge length obtained through the minimum spanning tree. The clusters NGC 2360, NGC 1960, IC 1442, King 21, and SAI 35 have ${\Gamma}{MSR}$ to be 1.65$\pm$0.18, 1.94$\pm$0.22, 2.21$\pm$0.20, 1.84$\pm$0.23, and 1.96$\pm$0.25, respectively which indicate moderate mass segregation in these clusters. The remaining five clusters are found to exhibit weak or no mass segregation. We used the ratio of half mass radius to the tidal radius i.e. R${h}$/R${t}$ to investigate the effect of the tidal interactions on the cluster structure and dynamics. The ratios of half mass radii to tidal radii are found to be positively correlated with the Galactocentric distances with a linear slope of 0.06$\pm$0.01 having linear regression coefficient r-square = 0.93 for the clusters.

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J. Maurya, Y. Joshi, M. Samal, et. al.
Fri, 21 Apr 23
27/60

Comments: 9 pages, 3 figures, 2 tables

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

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http://arxiv.org/abs/2304.09942


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

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

Comments: 28 pages, 34 figures

Giant planet engulfment by evolved giant stars: light curves, asteroseismology, and survivability [EPA]

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http://arxiv.org/abs/2304.09882


About ten percent of Sun-like ($1$-$2 M_\odot$) stars will engulf a $1$-$10 M_{\rm J}$ planet as they expand during the red giant branch (RGB) or asymptotic giant branch (AGB) phase of their evolution. Once engulfed, these planets experience a strong drag force in the star’s convective envelope and spiral inward, depositing energy and angular momentum. For these mass ratios, the inspiral takes $\sim 10$-$10^{2}$ years ($\sim 10^{2}$-$10^{3}$ orbits); the planet undergoes tidal disruption at a radius of $\sim R_\odot$. We use the Modules for Experiments in Stellar Astrophysics (MESA) software instrument to track the stellar response to the energy deposition while simultaneously evolving the planetary orbit. For RGB stars, as well as AGB stars with $M_{\rm p} \lesssim 5 M_{\rm J}$ planets, the star responds quasistatically but still brightens measurably on a timescale of years. In addition, asteroseismic indicators, such as the frequency spacing or rotational splitting, differ before and after engulfment. For AGB stars, engulfment of a $M_{\rm p} \gtrsim 5 M_{\rm J}$ planet drives supersonic expansion of the envelope, causing a bright, red, dusty eruption similar to a “luminous red nova.” Based on the peak luminosity, color, duration, and expected rate of these events, we suggest that engulfment events on the AGB could be a significant fraction of low-luminosity red novae in the Galaxy. We do not find conditions where the envelope is ejected prior to the planet’s tidal disruption, complicating the interpretation of short-period giant planets orbiting white dwarfs as survivors of common-envelope evolution.

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C. O’Connor, L. Bildsten, M. Cantiello, et. al.
Fri, 21 Apr 23
36/60

Comments: 24 pages, 11 figures, 1 table. Submitted to AAS Journals; revised after initial review. Comments welcome

Early-time spectroscopic modelling of the transitional Type Ia Supernova 2021rhu with TARDIS [HEAP]

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http://arxiv.org/abs/2304.10129


An open question in SN Ia research is where the boundary lies between ‘normal’ Type Ia supernovae (SNe Ia) that are used in cosmological measurements and those that sit off the Phillips relation. We present the spectroscopic modelling of one such ’86G-like’ transitional SN Ia, SN 2021rhu, that has recently been employed as a local Hubble Constant calibrator using a tip of the red-giant branch measurement. We detail its modelling from -12 d until maximum brightness using the radiative-transfer spectral-synthesis code tardis. We base our modelling on literature delayed-detonation and deflagration models of Chandrasekhar mass white dwarfs, as well as the double-detonation models of sub-Chandrasekhar mass white dwarfs. We present a new method for ‘projecting’ abundance profiles to different density profiles for ease of computation. Due to the small velocity extent and low outer densities of the W7 profile, we find it inadequate to reproduce the evolution of SN 2021rhu as it fails to match the high-velocity calcium components. The host extinction of SN 2021rhu is uncertain but we use modelling with and without an extinction correction to set lower and upper limits on the abundances of individual species. Comparing these limits to literature models we conclude that the spectral evolution of SN 2021rhu is also incompatible with double-detonation scenarios, lying more in line with those resulting from the delayed detonation mechanism (although there are some discrepancies, in particular a larger titanium abundance in SN 2021rhu compared to the literature). This suggests that SN 2021rhu is likely a lower luminosity, and hence lower temperature, version of a normal SN Ia.

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L. Harvey, K. Maguire, M. Magee, et. al.
Fri, 21 Apr 23
40/60

Comments: Comments: 25 pages, 22 figures, accepted for publication in MNRAS

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

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http://arxiv.org/abs/2304.10470


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

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

Comments: 33 pages, 31 figures; submitted to ApJ

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

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http://arxiv.org/abs/2304.10485


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

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

Comments: MNRAS, accepted for pubblication

Exploring the impact of IMF and binary parameter stochasticity with a binary population synthesis code [GA]

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http://arxiv.org/abs/2304.09549


Low mass star formation regions are unlikely to fully populate their initial mass functions, leading to a deficit of massive stars. In binary stellar populations, the full range of binary separations and mass ratios will also be underpopulated. To explore the effects of stochastic sampling in the integrated light of stellar clusters, we calculate models at a broad range of cluster masses, from 10^2 to 10^7 M_sun, using a binary stellar population synthesis code. For clusters with stellar masses less than 10^5 M_sun, observable quantities show substantial scatter and their mean properties reflect the expected deficit of massive stars. In common with previous work, we find that purely stochastic sampling of the initial mass function appears to underestimate the mass of the most massive star in known clusters. However, even with this constraint, the majority of clusters likely inject sufficient kinetic energy to clear their birth clusters of gas. For quantities which directly measure the impact of the most massive stars, such as N_{ion}, xi_{ion} and beta_{UV}, uncertainties due to stochastic sampling dominate over those from the IMF shape or distribution of binary parameters, while stochastic sampling has a negligible effect on the stellar continuum luminosity density.

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E. Stanway and J. Eldridge
Thu, 20 Apr 23
1/57

Comments: 15 pages and 8 page appendix. Accepted for publication in MNRAS

Constellations of co-orbital planets: horseshoe dynamics, long-term stability, transit timing variations, and potential as SETI beacons [EPA]

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http://arxiv.org/abs/2304.09209


Co-orbital systems contain two or more bodies sharing the same orbit around a planet or star. The best-known flavors of co-orbital systems are tadpoles (in which two bodies’ angular separations oscillate about the L4/L5 Lagrange points $60^\circ$ apart) and horseshoes (with two bodies periodically exchanging orbital energy to trace out a horseshoe shape in a co-rotating frame). Here, we use N-body simulations to explore the parameter space of many-planet horseshoe systems. We show that up to 24 equal-mass, Earth-mass planets can share the same orbit at 1 au, following a complex pattern in which neighboring planets undergo horseshoe oscillations. We explore the dynamics of horseshoe constellations, and show that they can remain stable for billions of years and even persist through their stars’ post-main sequence evolution. With sufficient observations, they can be identified through their large-amplitude, correlated transit timing variations. Given their longevity and exotic orbital architectures, horseshoe constellations may represent potential SETI beacons.

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S. Raymond, D. Veras, M. Clement, et. al.
Thu, 20 Apr 23
2/57

Comments: 10 pages, 10 figures. Published in MNRAS. YouTube playlist with animations of horseshoe constellation systems here: this https URL . Blog post here: this https URL

ASASSN-18aan revisited [SSA]

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http://arxiv.org/abs/2304.09829


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

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

Comments: 7 pages, 2 figures, published on OEJV

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

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http://arxiv.org/abs/2304.09642


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

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

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

Survival and dynamics of rings of co-orbital planets under perturbations [EPA]

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http://arxiv.org/abs/2304.09210


In co-orbital planetary systems, two or more planets share the same orbit around their star. Here we test the dynamical stability of co-orbital rings of planets perturbed by outside forces. We test two setups: i) ‘stationary’ rings of planets that, when unperturbed, remain equally-spaced along their orbit; and ii) horseshoe constellation systems, in which planets are continually undergoing horseshoe librations with their immediate neighbors. We show that a single rogue planet crossing the planets’ orbit more massive than a few lunar masses (0.01-0.04 Earth masses) systematically disrupts a co-orbital ring of 6, 9, 18, or 42 Earth-mass planets located at 1 au. Stationary rings are more resistant to perturbations than horseshoe constellations, yet when perturbed they can transform into stable horseshoe constellation systems. Given sufficient time, any co-orbital ring system will be perturbed into either becoming a horseshoe constellation or complete destabilization.

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S. Raymond, D. Veras, M. Clement, et. al.
Thu, 20 Apr 23
6/57

Comments: 5 pages, 4 figures. Re-submitted to MNRAS. Blog post about co-orbital constellations here: this https URL

Two super-Earths at the edge of the habitable zone of the nearby M dwarf TOI-2095 [EPA]

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http://arxiv.org/abs/2304.09220


The main scientific goal of TESS is to find planets smaller than Neptune around stars bright enough to allow further characterization studies. Given our current instrumentation and detection biases, M dwarfs are prime targets to search for small planets that are in (or nearby) the habitable zone of their host star. Here we use photometric observations and CARMENES radial velocity measurements to validate a pair of transiting planet candidates found by TESS. The data was fitted simultaneously using a Bayesian MCMC procedure taking into account the stellar variability present in the photometric and spectroscopic time series. We confirm the planetary origin of the two transiting candidates orbiting around TOI-2095 (TIC 235678745). The star is a nearby M dwarf ($d = 41.90 \pm 0.03$ pc, $T_{\rm eff} = 3759 \pm 87$ K, $V = 12.6$ mag) with a stellar mass and radius of $M_\star = 0.44 \pm 0.02 \; M_\odot$ and $R_\star = 0.44 \pm 0.02 \; R_\odot$, respectively. The planetary system is composed of two transiting planets: TOI-2095b with an orbital period of $P_b = 17.66484 \pm (7\times 10^{-5})$ days and TOI-2095c with $P_c = 28.17232 \pm (14\times 10^{-5})$ days. Both planets have similar sizes with $R_b = 1.25 \pm 0.07 \; R_\oplus$ and $R_c = 1.33 \pm 0.08 \; R_\oplus$ for planet b and c, respectively. We put upper limits on the masses of these objects with $M_b < 4.1 \; M_\oplus$ for the inner and $M_c < 7.4 \; M_\oplus$ for the outer planet (95\% confidence level). These two planets present equilibrium temperatures in the range of 300 – 350 K and are close to the inner edge of the habitable zone of their star.

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F. Murgas, A. Castro-González, E. Pallé, et. al.
Thu, 20 Apr 23
8/57

Comments: Submitted to Astronomy & Astrophysics

The quest for Magrathea planets I: formation of second generation exoplanets around double white dwarfs [EPA]

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http://arxiv.org/abs/2304.09204


The evolution of binaries that become double white dwarf (DWD) can cause the ejection of high amounts of dust and gas. Such material can give rise to circumbinary discs and become the cradle of new planets, yet no studies so far have focused on the formation of circumbinary planets around DWDs. These binaries will be the main sources of gravitational waves (GWs) detectable by the ESA Laser Interferometer Space Antenna (LISA) mission, opening the possibility to detect circumbinary planets around short-period DWDs everywhere in the Milky Way. We investigate the formation of Magrathea planets by simulating multiple planet formation tracks to explore how seeds growing first by pebble accretion, and then by gas accretion, are affected by the disc environments surrounding DWDs. We present both planetary formation tracks taking place in steady-state discs, and formation tracks taking place in discs evolving with time. The time-dependent tracks account for both the disc accretion rate onto the central binary and the disc photoevaporation rate caused by stellar irradiation. Our results show that planetary formation in circumbinary discs around DWDs can be possible. In particular, the extreme planetary formation environment implies three main significant results: (i) the accretion rate and the metallicity of the disc should be high in order to form sub-stellar objects with masses up to 31 M$J$, this is achieved only if planet formation starts soon after the onset of the disc and if first generation seeds are present in the disc; (ii) seeds formed within 0.1 Myr, or within 1 Myr, from the onset of the disc can only produce sub-Neptune and Neptunian planets, unless the disc accommodates first generation seeds with mass 10 M${\oplus}$; (iii) most of the planets are finally located within 1 au from the disc centre, while they are still undergoing the gas accretion phase.

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S. Ledda, C. Danielski and D. Turrini
Thu, 20 Apr 23
9/57

Comments: Accepted for publication in A&A on 05/04/2023, abstract shortened, 28 pages, 11 figures, 14 tables

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

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http://arxiv.org/abs/2304.09794


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

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

Comments: 15 pages, 1 figure, published in Frontiers

The spin and mass ratio affects the gravitational waveforms of binary black hole mergers with a total system mass of 12-130 $\rm{M}_\odot$ [HEAP]

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http://arxiv.org/abs/2304.09396


Analyzing the observations obtained by the LIGO and the Virgo Collaborations, a new era has begun in binary black hole (BBH) merger processes and black hole physics studies. The fact that very massive stars that will become black holes at the end of their evolution are in binary or multiple states adds particular importance to BBH studies. In this study, using the SEOBNRv4$_opt$ gravitational waveform model developed for compact binary systems, many ($\sim 10^6$) models were produced under different initial conditions, and the pre- and post-merge parameters were compared. In the models, it is assumed that the initial total mass (M${\rm{tot}}$) of the binary systems varies between 12-130 $\rm{M}\odot$ with step interval 1$\rm{M}\odot$, the mass ratios ($q = \rm{m}{1i}/\rm{m}{2i}$) vary between 1 and 2 with step interval 0.004, and the initial spin ($\abs{\rchi{1i}} = \abs{\rchi_{2i}}$) value varies between $-0.83$ and $+0.83$ with step interval 0.017. Final spin ($\rchi_{f}$), fractional mass loss (M${FL}$), and the maximum gravitational wave amplitude (h${\rm{max}}$) obtained during the merger were compared with appropriate tables and figures obtained from the results of the relativistic numeric model obtained according to the initial parameters. Our results show that M${\rm{FL}}$ in generated BBH coalescences varied about 2.7 to 9.2\%, and $\rchi{\rm{f}}$ between 0.29 and 0.91. In most of the BBHs we have modeled, we found that M${\rm{FL}}$ varies inversely with $q$. However, it has been found that M${\rm{FL}}$ values are not always inversely varied to the $q$ parameter in systems of opposite initial spin, where the large mass black hole component is positively oriented. Accordingly, it is understood that the values of M$_{\rm{FL}}$ decrease to a certain point of $q$ and then increase according to the increasing direction of $q$.

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&. Özbakır and K. Yakut
Thu, 20 Apr 23
23/57

Comments: 29 pages, 5 figure, 5 tables, submitted for publication

Internal kinematics and structure of the bulge globular cluster NGC 6569 [GA]

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http://arxiv.org/abs/2304.09472


In the context of a project aimed at characterizing the properties of star clusters in the Galactic bulge, here we present the determination of the internal kinematics and structure of the massive globular cluster NGC 6569. The kinematics has been studied by means of an unprecedented spectroscopic dataset acquired in the context of the ESO-VLT Multi-Instrument Kinematic Survey (MIKiS) of Galactic globular clusters, combining the observations from four different spectrographs. We measured the line-of-sight velocity of a sample of almost 1300 stars distributed between ~0.8″ and 770″ from the cluster center. From a sub-sample of high-quality measures, we determined the velocity dispersion profile of the system over its entire radial extension (from ~ 5″ to ~ 200″ from the center), finding the characteristic behavior usually observed in globular clusters, with a constant inner plateau and a declining trend at larger radii. The projected density profile of the cluster has been obtained from resolved star counts, by combining high-resolution photometric data in the center, and the Gaia EDR3 catalog radially extended out to ~20′ for a proper sampling of the Galactic field background. The two profiles are properly reproduced by the same King model, from which we estimated updated values of the central velocity dispersion, main structural parameters (such as the King concentration, the core, half-mass, and tidal radii), total mass, and relaxation times. Our analysis also reveals a hint of ordered rotation in an intermediate region of the cluster (40″<r<90″, corresponding to $ 2 r_c<r<4.5 r_c$), but additional data are required to properly assess this possibility.

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C. Pallanca, S. Leanza, F. Ferraro, et. al.
Thu, 20 Apr 23
28/57

Comments: Accepted for publication in The Astrophysical Journal; 21 pages, 10 figures, 4 tables

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

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http://arxiv.org/abs/2304.09786


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

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

Comments: N/A

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

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http://arxiv.org/abs/2304.09570


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

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

Comments: 24 pages, 10 figures

A blue depression in the optical spectra of M dwarfs [SSA]

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http://arxiv.org/abs/2304.09219


A blue depression is found in the spectra of M dwarfs from 4000 to 4500A. This depression shows an increase toward lower temperatures though is particularly sensitive to gravity and metallicity. It is the single most sensitive feature in the optical spectra of M dwarfs. The depression appears as centered on the neutral calcium resonance line at 4227A and leads to nearby features being weaker by about two orders of magnitude than predicted. We consider a variety of possible causes for the depression including temperature, gravity, metallicity, dust, damping constants, and atmospheric stratification. We also consider relevant molecular opacities which might be the cause identifying AlH, SiH, and NaH in the spectral region. However, none of these solutions are satisfactory. In the absence of a more accurate determination of the broadening of the calcium line perturbed by molecular hydrogen, we find a promising empirical fit using a modified Lorentzian line profile for the calcium resonance line. Such fits provide a simplistic line-broadening description for this calcium resonance line and potentially other un-modelled resonance lines in cool high-pressure atmospheres. Thus we claim the most plausible cause of the blue depression in the optical spectra of M dwarfs is a lack of appropriate treatment of line broadening for atomic calcium. The broad wings of the calcium resonance line develop at temperatures below about 4000K and are analogous to the neutral sodium and potassium features which dominate the red optical spectra of L dwarfs.

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H. Jones, Y. Pavlenko, Y. Lyubchik, et. al.
Thu, 20 Apr 23
49/57

Comments: Accepted in MNRAS

Black holes as the end state of stellar evolution: Theory and simulations [HEAP]

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http://arxiv.org/abs/2304.09350


The collapse of massive stars is one of the most-studied paths to black hole formation. In this chapter, we review black hole formation during the collapse of massive stars in the broader context of single and binary stellar evolution and the theory of supernova explosions. We provide a concise overview of the evolutionary channels that may lead to black hole formation — the classical route of iron core collapse, collapse due to pair instability in very massive stars, and the hypothetical scenario of supermassive star collapse. We then review the current understanding of the parameter space for black hole formation and black hole birth properties that has emerged from theoretical and computational modelling of supernova explosions and transient observations. Finally, we discuss what the intricate interplay between stellar evolution, stellar explosions, and binary interactions implies for the formation of stellar-mass black holes.

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A. Heger, B. Müller and I. Mandel
Thu, 20 Apr 23
51/57

Comments: 53 pages, 9 figures. This chapter is the pre-print of the version currently in production. Please cite this chapter as the following: A.Heger, B. M\”uller, and I. Mandel. “Black holes as the end state of stellar evolution: Theory and simulations,” in The Encyclopedia of Cosmology (Set 2): Black Holes, edited by Z. Haiman (World Scientific, New Jersey, 2023)

A Sun-like star orbiting a boson star [SSA]

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http://arxiv.org/abs/2304.09140


The high-precision astrometric mission GAIA recently reported the remarkable discovery of a Sun-like star closely orbiting a dark object, with a semi-major axis and period of $1.4\, \rm{AU}$ and $187.8$ days respectively. While the plausible expectation for the central dark object is a black hole, the evolutionary mechanism leading to the formation of such a two-body system is highly challenging. Here, we challenge the scenario of a central black hole and show that the observed orbital dynamics can be explained under fairly general assumptions if the central dark object is a stable clump of bosonic particles of spin-0, or spin-1, known as a boson star. We further explain how future astrometric measurements of similar systems will provide an exciting opportunity to probe the fundamental nature of compact objects and test compact alternatives to black holes.

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A. Pombo and I. Saltas
Wed, 19 Apr 23
8/58

Comments: 11 pages, 4 figures. Comments are very welcome

Mapping the Skies of Ultracool Worlds: Detecting Storms and Spots with Extremely Large Telescopes [EPA]

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http://arxiv.org/abs/2304.08518


Extremely large telescopes (ELTs) present an unparalleled opportunity to study the magnetism, atmospheric dynamics, and chemistry of very low mass stars (VLMs), brown dwarfs, and exoplanets. Instruments such as the Giant Magellan Telescope – Consortium Large Earth Finder (GMT/GCLEF), the Thirty Meter Telescope’s Multi-Objective Diffraction-limited High-Resolution Infrared Spectrograph (TMT/MODHIS), and the European Southern Observatory’s Mid-Infrared ELT Imager and Spectrograph (ELT/METIS) provide the spectral resolution and signal-to-noise (S/N) necessary to Doppler image ultracool targets’ surfaces based on temporal spectral variations due to surface inhomogeneities. Using our publicly-available code, $Imber$, developed and validated in Plummer & Wang (2022), we evaluate these instruments’ abilities to discern magnetic star spots and cloud systems on a VLM star (TRAPPIST-1); two L/T transition ultracool dwarfs (VHS J1256$-$1257 b and SIMP J0136+0933); and three exoplanets (Beta Pic b and HR 8799 d and e). We find that TMT/MODHIS and ELT/METIS are suitable for Doppler imaging the ultracool dwarfs and Beta Pic b over a single rotation. Uncertainties for longitude and radius are typically $\lesssim 10^{\circ}$, and latitude uncertainties range from $\sim 10^{\circ} \ \rm{to} \ 30^{\circ}$. TRAPPIST-1’s edge-on inclination and low $\upsilon \sin i$ provide a challenge for all three instruments while GMT/GCLEF and the HR 8799 planets may require observations over multiple rotations. We compare the spectroscopic technique, photometry-only inference, and the combination of the two. We find combining spectroscopic and photometric observations can lead to improved Bayesian inference of surface inhomogeneities and offers insight into whether ultracool atmospheres are dominated by spotted or banded features.

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M. Plummer and J. Wang
Wed, 19 Apr 23
11/58

Comments: Accepted for publication in The Astrophysical Journal, 26 pages, 10 figures, 3 tables

The dynamical mass of the white dwarf in XY Ari questions intermediate polar X-ray spectral models [SSA]

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http://arxiv.org/abs/2304.08524


We present a dynamical study of the eclipsing intermediate polar XY Ari based on time-resolved near-infrared spectroscopy obtained with the EMIR spectrograph on the 10.4-m Gran Telescopio Canarias. Using main sequence template spectra taken with the same instrument setup as the target spectra, we measure a radial velocity amplitude of the late K-type donor star $K_2=256 \pm 2$ km s$^{-1}$. We also obtain the rotational broadening of its photospheric lines $v_\mathrm{rot} \sin i = 141 \pm 3$ km s$^{-1}$. From these and the eclipse geometry, we derive a donor-to-white dwarf mass ratio $q = M_2/M_1 = 0.62 \pm 0.02$, an orbital inclination $i = 80.8^{\circ} \pm 0.5^{\circ}$ and dynamical masses $M_{1} = 1.21 \pm 0.04 \, \mathrm{M}{\odot}$ and $M_2 = 0.75 \pm 0.04 \, \mathrm{M}{\odot}$ ($1 \sigma$). This result places the white dwarf in XY Ari as one of the three most massive known in a cataclysmic variable. Comparison with a number of white dwarf mass estimates from X-ray spectral modelling indicates the necessity of a major revision of the cooling models currently assumed for magnetic accretion in intermediate polars, as most of the X-ray white dwarf masses lie significantly below the dynamical mass value.

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A. Álvarez-Hernández, M. Torres, P. Rodríguez-Gil, et. al.
Wed, 19 Apr 23
17/58

Comments: 9 pages, 4 figures, 5 tables, submitted for publication in MNRAS

Ultra-high-resolution Observations of Persistent Null-point Reconnection in the Solar Corona [SSA]

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http://arxiv.org/abs/2304.08725


Magnetic reconnection is a key mechanism involved in solar eruptions and is also a prime possibility to heat the low corona to millions of degrees. Here, we present ultra-high-resolution extreme ultraviolet observations of persistent null-point reconnection in the corona at a scale of about 390 km over one hour observations of the Extreme-Ultraviolet Imager on board Solar Orbiter spacecraft. The observations show formation of a null-point configuration above a minor positive polarity embedded within a region of dominant negative polarity near a sunspot. The gentle phase of the persistent null-point reconnection is evidenced by sustained point-like high-temperature plasma (about 10 MK) near the null-point and constant outflow blobs not only along the outer spine but also along the fan surface. The blobs appear at a higher frequency than previously observed with an average velocity of about 80 km/s and life-times of about 40 s. The null-point reconnection also occurs explosively but only for 4 minutes, its coupling with a mini-filament eruption generates a spiral jet. These results suggest that magnetic reconnection, at previously unresolved scales, proceeds continually in a gentle and/or explosive way to persistently transfer mass and energy to the overlying corona.

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X. Cheng, E. Priest, H. Li, et. al.
Wed, 19 Apr 23
24/58

Comments: 27 pages, 7 figures

The progenitors of Type Ia supernovae with asymptotic giant branch donors [SSA]

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http://arxiv.org/abs/2304.08839


Type Ia supernovae (SNe Ia) are among the most energetic events in the Universe. They are excellent cosmological distance indicators due to the remarkable homogeneity of their light curves. However, the nature of the progenitors of SNe Ia is still not well understood. In the single-degenerate model, a carbon-oxygen white dwarf (CO WD) could grow its mass by accreting material from an asymptotic giant branch (AGB) star, leading to the formation of SNe Ia when the mass of the WD approaches to the Chandrasekhar-mass limit, known as the AGB donor channel. In this channel, previous studies mainly concentrate on the wind-accretion pathway for the mass-increase of the WDs. In the present work, we employed an integrated mass-transfer prescription for the semidetached WD+AGB systems, and evolved a number of WD+AGB systems for the formation of SNe Ia through the Roche-lobe overflow process or the wind-accretion process. We provided the initial and final parameter spaces of WD+AGB systems for producing SNe Ia. We also obtained the density distribution of circumstellar matter at the moment when the WD mass reaches the Chandrasekhar-mass limit. Moreover, we found that the massive WD+AGB sample AT 2019qyl can be covered by the final parameter space for producing SNe Ia, indicating that AT 2019qyl is a strong progenitor candidate of SNe Ia with AGB donors.

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L. Li, D. Liu and B. Wang
Wed, 19 Apr 23
27/58

Comments: 12 pages, 5 figures, accepted for publication in Res. Astron. Astrophys

Bayesian averaging for ground state masses of atomic nuclei in a Machine Learning approach [CL]

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http://arxiv.org/abs/2304.08546


We present global predictions of the ground state mass of atomic nuclei based on a novel Machine Learning (ML) algorithm. We combine precision nuclear experimental measurements together with theoretical predictions of unmeasured nuclei. This hybrid data set is used to train a probabilistic neural network. In addition to training on this data, a physics-based loss function is employed to help refine the solutions. The resultant Bayesian averaged predictions have excellent performance compared to the testing set and come with well-quantified uncertainties which are critical for contemporary scientific applications. We assess extrapolations of the model’s predictions and estimate the growth of uncertainties in the region far from measurements.

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M. Mumpower, M. Li, T. Sprouse, et. al.
Wed, 19 Apr 23
28/58

Comments: 15 pages, 10 figures, comments welcome

Mass measurements and 3D orbital geometry of PSR J1933$-$6211 [HEAP]

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http://arxiv.org/abs/2304.09060


PSR J1933$-$6211 is a 3.5-ms pulsar in a 12.8-d orbit with a white dwarf (WD). Its high proper motion and low dispersion measure result in such significant interstellar scintillation that high signal-to-noise detections require long observing durations or fortuitous timing. We turn to the sensitive MeerKAT telescope and, combined with historic Parkes data, leverage PSR J1933$-$6211’s kinematic and relativistic effects to constrain its 3D orbital geometry and the component masses. We obtain precise proper motion and parallax estimates, and measure their effects as secular changes in the Keplerian orbital parameters: a variation in orbital period of $7(1) \times 10^{-13}$ s s$^{-1}$ and a change in projected semi-major axis of $1.60(5) \times 10^{-14}$ s s$^{-1}$. A self-consistent analysis of all kinematic and relativistic effects yields a distance of $1.6^{+0.2}{-0.3}$ kpc, an orbital inclination, $i = 55(1)$ deg and a longitude of the ascending node, $\Omega = 255^{+8}{-14}$ deg. The probability densities for $\Omega$ and $i$ and their symmetric counterparts, ($180-i$, $360-\Omega$), are seen to depend on the fiducial orbit used to measure the time of periastron passage. We investigate this unexpected dependence and rule out software-related causes using simulations. Nevertheless, we constrain the pulsar and WD masses to $1.4^{+0.3}{-0.2}$ M$\odot$ and $0.43(5)$ M$\odot$ respectively. These strongly disfavour a helium-dominated WD. The orbital similarities between PSRs J1933$-$6211 and J1614$-$2230 suggest they underwent Case A Roche lobe overflow, an extended evolution while the companion star is still on the Main Sequence. However, with a mass of $\sim 1.4$ M$\odot$, PSR J1933$-$6211 has not accreted significant matter. This highlights the low accretion efficiency of the spin-up process and suggests that observed neutron star masses are mostly a result of supernova physics.

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M. Geyer, V. Krishnan, P. Freire, et. al.
Wed, 19 Apr 23
31/58

Comments: 16 pages, 7 figures. Abstract shortened to adhere to ArXiv limit

The evolutionary route to form planetary nebulae with central neutron star – white dwarf binaries [HEAP]

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http://arxiv.org/abs/2304.08827


We present a possible evolutionary pathway to form planetary nebulae (PNe) with close neutron star (NS)-white dwarf (WD) binary central stars. By employing a comprehensive binary population synthesis technique we find that the evolution involves two common envelope evolution (CEE) phases and a core collapse supernova explosion between them that forms the NS. Later the lower mass star engulfs the NS as it becomes a red giant, a process that leads to the second CEE phase and to the ejection of the envelope. This leaves a hot horizontal branch star that evolves to become a helium WD and an expanding nebula. Both the WD and the NS power the nebula. The NS in addition might power a pulsar wind nebula inside the expanding PN. From our simulations we find that the Galactic formation rate of NS-WD PNe is $1.8 \times 10^{-5} {\rm yr}^{-1}$ while the Galactic formation rate of all PNe is $0.42 {\rm yr}^{-1}$. There is a possibility that one of the observed Galactic PNe might be a NS-WD PN, and a few NS-WD PNe might exist in the Galaxy. The central binary systems might be sources for future gravitational wave detectors like LISA, and possibly of electromagnetic telescopes.

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I. Ablimit and N. Soker
Wed, 19 Apr 23
41/58

Comments: 8 pages, 4 figures, one appendix with 3 tables; Will be submitted to MNRAS, comments welcome

Combined Spectroscopic and Photometric Analysis of Flares in the Dwarf M Star EV Lacertae [SSA]

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http://arxiv.org/abs/2304.08578


We report results of an observing campaign to study the dwarf M flare star EV Lacertae. Between October 2021 and January 2022 we obtained concurrent B band photometry and low resolution spectroscopy of EV Lac on 39 occasions during 10 of which we observed flares with amplitude greater than 0.1 magnitude. Spectra were calibrated in absolute flux using concurrent photometry and flare-only spectra obtained by subtracting mean quiescent spectra. We measured B band flare energies between Log E = 30.8 and 32.6 erg. In the brightest flares we measured temporal development of flare flux in H I and He I emission lines and in the adjacent continuum and found that flux in the continuum subsided more rapidly than in the emission lines. Although our time resolution was limited, in our brightest flare we saw flux in the continuum clearly peaking before flux in the emission lines. We observed a progressive decrease in flare energy from H\b{eta} to H{\delta}. On average we found 37% of B band flare energy appeared in the H\b{eta} to H{\epsilon} emission lines with the remainder contributing to a rise in continuum flux. We measured black-body temperatures for the brightest flares between 10,500 +- 700 K and 19,500 +- 500 K and found a linear relationship between flare temperature and continuum flux at 4170 {\AA}. Balmer lines in flare-only spectra were well fitted by Gaussian profiles with some evidence of additional short-lived blue-shifted emission at the flare peak.

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D. Boyd, R. Buchheim, S. Curry, et. al.
Wed, 19 Apr 23
43/58

Comments: 12 pages, 13 figures, accepted for publication in the Journal of the AAVSO

On the seed population of solar energetic particles in the inner heliosphere [CL]

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http://arxiv.org/abs/2304.09098


Particles measured in large gradual solar energetic particle (SEP) events are believed to be predominantly accelerated at shocks driven by coronal mass ejections (CMEs). Ion charge state and composition analyses suggest that the origin of the seed particle population for the mechanisms of particle acceleration at CME-driven shocks is not the bulk solar wind thermal material, but rather a suprathermal population present in the solar wind. This suprathermal population could result from remnant material accelerated in prior solar flares and/or preceding CME-driven shocks. In this work, we examine the distribution of this suprathermal particle population in the inner heliosphere by combining a magnetohydrodynamic (MHD) simulation of the solar wind and a Monte-Carlo simulation of particle acceleration and transport. Assuming that the seed particles are uniformly distributed near the Sun by solar flares of various magnitudes, we study the longitudinal distribution of the seed population at multiple heliocentric distances. We consider a non-uniform background solar wind, consisting of fast and slow streams that lead to compression and rarefaction regions within the solar wind. Our simulations show that the seed population at a particular location (e.g., 1 au) is strongly modulated by the underlying solar wind configuration. Corotating interaction regions (CIRs) and merged interactions regions (MIRs) can strongly alter the energy spectra of the seed particle populations. In addition, cross-field diffusion plays an important role in mitigating strong variations of the seed population in both space and energy.

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N. Wijsen, G. Li, Z. Ding, et. al.
Wed, 19 Apr 23
52/58

Comments: 20 pages, 7 figures

Emerging planetary nebulae within 3D spiral patterns [SSA]

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http://arxiv.org/abs/2304.08668


We present the first 3D radiation-hydrodynamic simulations of the formation of planetary nebulae (PNe) emerging from 3D spiral patterns. We use the GUACHO code to create 3D spiral structures as a consequence of the distortions on the geometry of the intrinsically isotropic wind of an asymptotic giant branch (AGB) star produced by a companion star in a circular orbit. We found that the orbital period of the binary producing the 3D spiral pattern has consequences on the formation and shaping of the PN itself. Stellar systems with longer period create less entwined 3D spirals, producing PNe with rounder inner cavities, and prevent the expansion of jet towards the polar directions. The spiral fitting procedure used in the literature to predict the binary’s orbital period may be misleading in the case of proto-PNe and PNe as spiral patterns are diluted by their own thermal expansion down to the average AGB density profile within a few hundred years and are further disrupted by the action of jets. By adopting a phase of jet ejections between the AGB and post-AGB stages, we are able to recover the morphologies of proto-PNe and PNe that exhibit ring-like structures in their halos.

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V. Lora, J. Toalá, J. González-Carbajal, et. al.
Wed, 19 Apr 23
54/58

Comments: 12 pages, 12 figures, 1 table; Accepted to MNRAS

The cosmic waltz of Coma Berenices and Latyshev 2 (Group X). Membership, phase-space structure, mass, and energy distributions [SSA]

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http://arxiv.org/abs/2304.08618


Context. Open clusters (OCs) are fundamental benchmarks where theories of star formation and stellar evolution can be tested and validated. Coma Ber and Latyshev 2 (Group X) are the second and third OCs closest to the Sun, making them excellent targets to search for low-mass stars and ultra-cool dwarfs. In addition, this pair will experience a flyby in 10-16 Myr which makes it a benchmark to test OCs pair interactions. Aims. We aim at analysing the membership, luminosity, mass, phase-space (i.e., positions and velocities), and energy distributions for Coma Ber and Latyshev 2 and test the hypothesis of the mixing of their populations at the encounter time. Methods. We develop a new phase-space membership methodology and apply it to Gaia data. With the recovered members we infer the phase-space, luminosity and mass distributions using publicly available Bayesian inference codes. Then, with a publicly available orbit integration code and members’ positions and velocities, we integrate their orbits 20 Myr into the future. Results. In Coma Ber, we identify 302 candidate members distributed in the core and tidal tails. The tails are dynamically cold and asymmetrically populated. The stellar system called Group X is made of two structures: the disrupted OC Latyshev 2 (186 candidate members) and a loose stellar association called Mecayotl 1 (146 candidate members), both of them will fly by Coma Ber in $11.3\pm0.5$ Myr and $14.0\pm0.6$ Myr, respectively, and each other in $8.1\pm1.3$ Myr. Conclusions. We study the dynamical properties of the core and tails of Coma Ber and also confirm the existence of the OC Latyshev 2 and its neighbour stellar association Mecayotl 1. Although these three systems will experience encounters we find no evidence supporting the mixing of their populations.

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J. Olivares, N. Lodieu, V. Béjar, et. al.
Wed, 19 Apr 23
58/58

Comments: 25 pages, 19 figures, accepted for publication in Astronomy & Astrophysics

The Breakthrough Listen Search for Intelligent Life: Nearby Stars' Close Encounters with the Brightest Earth Transmissions [SSA]

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http://arxiv.org/abs/2304.07400


After having left the heliosphere, Voyager 1 and Voyager 2 continue to travel through interstellar space. The Pioneer 10, Pioneer 11, and New Horizons spacecraft are also on paths to pass the heliopause. These spacecraft have communicated with the Deep Station Network (DSN) radio antennas in order to download scientific data and telemetry data. Outward transmissions from DSN travel to the spacecraft and beyond into interstellar space. These transmissions have encountered and will encounter other stars, introducing the possibility that intelligent life in other solar systems will encounter our terrestrial transmissions. We use the beamwidth of the transmissions between DSN and interstellar spacecraft to perform a search around the past and future positions of each spacecraft obtained from the JPL Horizons System. By performing this search over the Gaia Catalogue of Nearby Stars (GCNS), a catalogue of precisely mapped stars within 100 pc, we determine which stars the transmissions of these spacecraft will encounter. We highlight stars that are in the background of DSN transmissions and calculate the dates of these encounters to determine the time and place for potential intelligent extraterrestrial life to encounter terrestrial transmissions.

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R. Derrick and H. Isaacson
Tue, 18 Apr 23
5/80

Comments: N/A

Detached and Continuous Circumstellar Matter in Type Ibc Supernovae from Mass Eruption [HEAP]

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http://arxiv.org/abs/2304.08378


Some hydrogen-poor supernovae (SNe) are found to undergo interaction with dense circumstellar matter (CSM) that may originate from mass eruption(s) just prior to core-collapse. We model the interaction between the remaining star and the bound part of the erupted CSM that eventually fall back to the star. We find that while fallback initially results in a continuous CSM down to the star, feedback processes from the star can push the CSM to large radii of $\gtrsim 10^{15}$ cm from several years after the eruption. In the latter case, a tenuous bubble surrounded by a dense and detached CSM extending to $\gtrsim 10^{16}$ cm is expected. Our model offers a natural unifying explanation for the diverse CSM structures seen in hydrogen-poor SNe, such as Type Ibn/Icn SNe that show CSM signatures soon after explosion, and the recently discovered Type Ic SNe 2021ocs and 2022xxf (“the Bactrian”) with CSM signatures seen only at late times.

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D. Tsuna and Y. Takei
Tue, 18 Apr 23
7/80

Comments: 6 pages, 4 Figures. To be submitted to PASJ letters in the weekend

Spectral classification of young stars using conditional invertible neural networks I. Introducing and validating the method [SSA]

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http://arxiv.org/abs/2304.08398


Aims. We introduce a new deep learning tool that estimates stellar parameters (such as effective temperature, surface gravity, and extinction) of young low-mass stars by coupling the Phoenix stellar atmosphere model with a conditional invertible neural network (cINN). Our networks allow us to infer the posterior distribution of each stellar parameter from the optical spectrum.
Methods. We discuss cINNs trained on three different Phoenix grids: Settl, NextGen, and Dusty. We evaluate the performance of these cINNs on unlearned Phoenix synthetic spectra and on the spectra of 36 Class III template stars with well-characterised stellar parameters.
Results. We confirm that the cINNs estimate the considered stellar parameters almost perfectly when tested on unlearned Phoenix synthetic spectra. Applying our networks to Class III stars, we find good agreement with deviations of at most 5–10 per cent. The cINNs perform slightly better for earlier-type stars than for later-type stars like late M-type stars, but we conclude that estimations of effective temperature and surface gravity are reliable for all spectral types within the network’s training range.
Conclusions. Our networks are time-efficient tools applicable to large amounts of observations. Among the three networks, we recommend using the cINN trained on the Settl library (Settl-Net), as it provides the best performance across the largest range of temperature and gravity.

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D. Kang, V. Ksoll, D. Itrich, et. al.
Tue, 18 Apr 23
8/80

Comments: 29 pages, 19 figures, Accepted for publication by Astronomy & Astrophysics on 10. April

Spectroscopic follow-up of black hole and neutron star candidates in ellipsoidal variables from Gaia DR3 [SSA]

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http://arxiv.org/abs/2304.07324


We present multi-epoch spectroscopic follow-up of a sample of ellipsoidal variables selected from Gaia DR3 as candidates for hosting quiescent black holes (BHs) and neutron stars (NSs). Our targets were identified as BH/NS candidates because their optical light curves — when interpreted with models that attribute variability to tidal distortion of a star by a companion that contributes negligible light — suggest that the companions are compact objects. From the likely BH/NS candidates identified in recent work accompanying Gaia DR3, we select 14 of the most promising targets for follow-up. We obtained spectra for each object at 2-10 epochs, strategically observing near conjunction to best-constrain the radial velocity semi-amplitude. From the measured semi-amplitudes of the radial velocity curves, we derive minimum companion masses of $M_{2,\min} \leq 0.5 ~ M_{\odot}$ in all cases. Assuming random inclinations, the typical inferred companion mass is $M_2 \sim 0.15 ~ M_{\odot}$. This makes it unlikely that any of these systems contain a BH or NS, and we consider alternative explanations for the observed variability. We can best reproduce the observed light curves and radial velocities with models for unequal-mass contact binaries with starspots. Some of the objects in our sample may also be detached main-sequence binaries, or even single stars with pulsations or starspot variability masquerading as ellipsoidal variation. We provide recommendations for future spectroscopic efforts to further characterize this sample and more generally to search for compact object companions in close binaries.

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P. Nagarajan, K. El-Badry, A. Rodriguez, et. al.
Tue, 18 Apr 23
12/80

Comments: 18 pages, 12 figures

Residual eccentricity of an Earth-like planet orbiting a red giant Sun [EPA]

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http://arxiv.org/abs/2304.07808


The late phases of the orbital evolution of an Earth-like planet around a Sun-like star are revisited considering the effect of the density fluctuations associated with convective motions inside the star. Such fluctuations produce a random perturbation of the stellar outer gravitational field that excites a small residual eccentricity in the orbit of the planet counteracting the effects of tides that tend to circularize the orbit. We compute the power spectrum of the outer gravitational field fluctuations of the star in the quadrupole approximation and study their effects on the orbit of the planet using a perturbative approach. The residual eccentricity is found to be a stochastic variable showing a Gaussian distribution. Adopting a model of the stellar evolution of our Sun computed with MESA, we find that the Earth will be engulfed close to the tip of the red giant branch evolution phase. We find a maximum mean value of the residual eccentricity of about 0.026 immediately before the engulfment. Considering an Earth-mass planet with an initial orbital semimajor axis sufficiently large to escape engulfment, we find that the mean value of the residual eccentricity is greater than 0.01 for an initial separation up to about 1.4 au. The engulfment of the Earth by the red giant Sun is found to be a stochastic process, in contrast to the deterministic character assumed in previous studies. If an Earth-like planet escapes engulfment, its orbit around its remnant white dwarf star will be moderately eccentric. Such a residual eccentricity on the order of a few hundredths can play a relevant role in sustaining the pollution of the white dwarf atmosphere by asteroids and comets as observed in several objects.

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A. Lanza, Y. Lebreton and C. Sallard
Tue, 18 Apr 23
15/80

Comments: 18 pages, 6 figures, 3 appendixes, accepted by Astronomy & Astrophysics

Precise Age for the Binary Star System 12 Com in the Coma Berenices Cluster [SSA]

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http://arxiv.org/abs/2304.07397


We present measurements of the interferometrically-resolved binary star system 12 Com and the single giant star 31 Com in the cluster Coma Berenices. 12 Com is a double-lined spectroscopic binary system consisting of a G7 giant and an A3 dwarf at the cluster turnoff. Using an extensive radial velocity dataset and interferometric measurements from PTI and the CHARA array, we measured masses $M_1 =2.64 \pm 0.07 M_\odot$ and $M_2 =2.10 \pm 0.03 M_\odot$. Interferometry also allows us to resolve the giant, and measure its size as $R_1 = 9.12 \pm 0.12 \pm 0.01 R_\odot$. With the measured masses and radii, we find an age of $533 \pm 41 \pm 42$ Myr. For comparison, we measure the radius of 31 Com to be $8.36 \pm 0.15 R_\odot$. Based on the photometry and radius measurements, 12 Com A is likely the most evolved bright star in the cluster, large enough to be in the red giant phase, but too small to have core helium burning. Simultaneous knowledge of 12 Com A’s mass and photometry puts strong constraints on convective core overshooting during the main sequence phase, which in turn reduces systematic uncertainties in the age. Increased precision in measuring this system also improves our knowledge of the progenitor of the cluster white dwarf WD1216+260.

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R. Lam, E. Sandquist, G. Schaefer, et. al.
Tue, 18 Apr 23
17/80

Comments: N/A

On the 5-Minute Oscillations of Photospheric and Chromospheric Swirls [SSA]

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http://arxiv.org/abs/2304.07970


Swirls are ubiquitous in the solar atmosphere. They are believed to be related to the excitation of different modes of magnetohydrodynamic waves and pulses, as well as spicules. However, statistical studies of their collective behaviour are rare. In this paper, we aim to study the collective, as well as the behaviour of individual photospheric and chromospheric swirls detected by the automated swirl detection algorithm (ASDA) from observations obtained by the Swedish 1-m Solar Telescope and the Hinode satellite. Detailed analysis of six different parameters of photospheric and chromospheric swirls is performed employing the wavelet analysis. Two clusters of periods with significant wavelet power, one from $3-8$ minutes and the other from $10-14$ minutes, have been found. The former coincides with the dominant period of the global $p$-mode spectrum. Wavelet and Fast Fourier Transform (FFT) analysis of example swirls also reveals similar periods. These results suggest that global $p$-modes might be important for triggering photospheric and thus chromospheric swirls. A novel scenario of global $p$-modes providing energy and mass fluxes to the upper solar atmosphere via generating swirls, Alfv\’en pulses and spicules is then proposed.

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J. Liu, D. Jess, R. Erdélyi, et. al.
Tue, 18 Apr 23
26/80

Comments: 8 figures and 3 tables, to be published in A&A

Variable stars in the residual light curves of OGLE-IV eclipsing binaries towards the Galactic Bulge [SSA]

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http://arxiv.org/abs/2304.08394


Context. The Optical Gravitational Lensing Experiment (OGLE) observed around 450,000 eclipsing binaries (EBs) towards the Galactic Bulge. Decade-long photometric observations such as these provide an exceptional opportunity to thoroughly examine the targets. However, observing dense stellar fields such as the Bulge may result in blends and contamination by close objects.
Aims. We searched for periodic variations in the residual light curves of EBs in OGLE-IV and created a new catalogue for the EBs that contain `background’ signals after the investigation of the source of the signal.
Methods. From the about half a million EB systems, we selected those that contain more than 4000 data points. We fitted the EB signal with a simple model and subtracted it. To identify periodical signals in the residuals, we used a GPU-based phase dispersion minimisation python algorithm called cuvarbase and validated the found periods with Lomb-Scargle periodograms. We tested the reliability of our method with artificial light curves.
Results. We identified 354 systems where short-period background variation was significant. In these cases, we determined whether it is a new variable or just the result of contamination by an already catalogued nearby one. We classified 292 newly found variables into EB, $\delta$ Scuti, or RR Lyrae categories, or their sub-classes, and collected them in a catalogue. We also discovered four new doubly eclipsing systems and one eclipsing multiple system with a $\delta$ Scuti variable, and modelled the outer orbits of the components.

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R. Ádám, T. Hajdu, A. Bódi, et. al.
Tue, 18 Apr 23
30/80

Comments: 22 pages, 17 figures, 7 tables, accepted for publication in Astronomy & Astrophysics

Three-dimensional magnetic field imaging of protoplanetary disks using Zeeman broadening and linear polarization observations [EPA]

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http://arxiv.org/abs/2304.07346


Magnetic fields are predicted to have a crucial impact on the structure, evolution and chemistry of protoplanetary disks. However, a direct detection of the magnetic field towards these objects has yet to be achieved. In order to characterize protoplanetary disk magnetic fields, we investigate the impact of the Zeeman effect on the (polarized) radiative transfer of emission from paramagnetic molecules excited in protoplanetary disks. While the effects of the Zeeman effect are commonly studied in the circular polarization of spectral lines, we perform a comprehensive modeling also of the Zeeman-induced broadening of spectral lines and their linear polarization. We develop simplified radiative transfer models adapted to protoplanetary disks, which we compare to full three-dimensional polarized radiative transfer simulations. We find that the radiative transfer of circular polarization is heavily affected by the expected polarity-change of the magnetic field between opposite sides of the disk. In contrast, Zeeman broadening and linear polarization are relatively unaffected by this sign change due to their quadratic dependence on the magnetic field. We can match our simplified radiative transfer models to full polarization modeling with high fidelity, which in turn allows us to prescribe straight-forward methods to extract magnetic field information from Zeeman broadening and linear polarization observations. We find that Zeeman broadening and linear polarization observations are highly advantageous methods to characterize protoplanetary disk magnetic fields as they are both sensitive probes of the magnetic field and are marginally affected by any sign change of the disk magnetic field. Applying our results to existing circular polarization observations of protoplanetary disk spectral lines suggests that the current upper limits on the toroidal magnetic field strengths have to be raised.

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B. Lankhaar and R. Teague
Tue, 18 Apr 23
31/80

Comments: 22 pages, 10 figures, accepted to A&A

Empirical measurement of the dynamical ages of three globular clusters and some considerations on the use of the dynamical clock [GA]

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http://arxiv.org/abs/2304.08140


We have used the “dynamical clock” to measure the level of dynamical evolution reached by three Galactic globular clusters (namely, NGC 3201, NGC 6316 and NGC 6440). This is an empirical method that quantifies the level of central segregation of blue stragglers stars (BSSs) within the cluster half-mass radius by means of the $A^+{rh}$ parameter, defined as the area enclosed between the cumulative radial distribution of BSSs and that of a lighter population. The total sample with homogeneous determinations of $A^+{rh}$ now counts a gran-total of 59 clusters: 52 old GCs in the Milky Way (including the three investigated here), 5 old clusters in the Large Magellanic Cloud, and 2 young systems in the Small Magellanic Cloud. The three objects studied here nicely nest into the correlation between $A^+_{rh}$ and the central relaxation time defined by the previous sample, thus proving and consolidating the use of the dynamical clock as an excellent tracer of the stage of star cluster dynamical evolution in different galactic environments. Finally, we discuss the advantages of using the dynamical clock as an indicator of star cluster dynamical ages, compared to the present-day central relaxation time.

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F. Ferraro, B. Lanzoni, E. Vesperini, et. al.
Tue, 18 Apr 23
33/80

Comments: 16 pages and 8 figures, in press in the ApJ

Multiple Stellar Populations in Globular Clusters with JWST [SSA]

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http://arxiv.org/abs/2304.07770


I present the first evidence of multiple populations in the globular cluster (GCs) 47Tucanae based on images collected with the near-infrared camera (NIRCam) on board the James Webb Space Telescope (JWST). While NIRCam photometry is poorly sensitive to multiple populations among stars brighter than the main-sequence (MS) knee, the M-dwarfs more-massive than 0.1 solar masses define a wide F115W-F322W2 color range due to multiple populations. The star-to-star color differences are mostly due to the different amounts of water vapor (hence oxygen) that affect the spectra of M-dwarfs. The chromosome map unveils an extended first population (1P) composed of M-dwarfs with different metallicities and three main groups of second-population (2P) stars that are depleted in oxygen with respect to the 1P. I present the discovery of an MS of very-low-mass stars (masses smaller than 0.1 solar masses) and tentatively associated it with a sequence composed of O-rich stars alone.

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A. Milone
Tue, 18 Apr 23
38/80

Comments: Four pages and two figures. Proceedings of the IAUS 377: Early Disk-Galaxy Formation from JWST to the Milky Way. Kuala-Lumpur,February 6-10, 2023

Proposed Resolution to the Solar Open Magnetic Flux Problem [SSA]

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http://arxiv.org/abs/2304.07649


The solar magnetic fields emerging from the photosphere into the chromosphere and corona are comprised of a combination of “closed” and “open” fields. The closed magnetic field lines are defined as those having both ends rooted in the solar surface, while the open field lines are those having one end extending out into interplanetary space and the other rooted at the Sun’s surface. Since the early 2000’s, the amount of total unsigned open magnetic flux estimated by coronal models have been in significant disagreement with in situ spacecraft observations, especially during solar maximum. Estimates of total open unsigned magnetic flux using coronal hole observations (e.g., using extreme ultraviolet (EUV) or Helium (He) I) are in general agreement with the coronal model results and thus show similar disagreements with in situ observations. While several possible sources producing these discrepancies have been postulated over the years, there is still no clear resolution to the problem. This paper provides a brief overview of the problem and summarizes some proposed explanations for the discrepancies. In addition, two different ways of estimating the total unsigned open magnetic flux are presented, utilizing the Wang-Sheeley-Arge (WSA) model, and one of the methods produce surprisingly good agreement with in situ observations. The findings presented here suggest that active regions residing near the boundaries of mid-latitude coronal holes are the probable source of the missing open flux. This explanation also brings in line many of the seemly contradictory facts that have made resolving this problem so difficult.

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C. Arge, A. Leisner, S. Wallace, et. al.
Tue, 18 Apr 23
41/80

Comments: 14 pages, 5 figures

Chemical Compositions of Red Giant Stars in the Old Open Cluster NGC 7789 [SSA]

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http://arxiv.org/abs/2304.07359


We have gathered optical-region spectra, derived model atmosphere parameters, and computed elemental abundances for 15 red giant stars in the open cluster NGC 7789. We focus on the light element group CNOLi that provides clues to evolutionary changes associated with internal fusion events and chemical mixing. We confirm and extend an early report that NGC 7789 stars 193 and 301 have anomalously large Li abundances, and that these values are apparently unconnected to any other elements’ abundances in these stars. A companion study of He I lambda 10830 lines in both field stars and cluster members shows that star 301 has a strong He feature while star 193 does not. Possible explanations for the large Li abundances of these stars include helium flash-induced mixing events and binary interactions at some past or present times. In either case an internal eruption of energy could cause fresh synthesis of lithium via the Cameron-Fowler Beryllium transport mechanism. Rapid transport of lithium to the outer layers may have created significant chromospheric transient disturbances, producing enough helium ionization to allow for the strong lambda 10830 absorption in star 301.

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N. Nagarajan, C. Sneden, M. Afsar, et. al.
Tue, 18 Apr 23
42/80

Comments: AJ, in press

The Stellar Spectra Factory (SSF) Based On SLAM [SSA]

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http://arxiv.org/abs/2304.08089


In this work, we present Stellar Spectra Factory (SSF), a tool to generate empirical-based stellar spectra from arbitrary stellar atmospheric parameters. The relative flux-calibrated empirical spectra can be predicted by SSF given arbitrary effective temperature, surface gravity, and metallicity. SSF constructs the interpolation approach based on the SLAM, using ATLAS-A library as the training dataset. SSF is composed of 4 data-driven sub-models to predict empirical stellar spectra. SSF-N can generate spectra from A to K type and some M giant stars, covering 3700 < Teff < 8700 K, 0 < logg < 6 dex, and -1.5 < [M/H] < 0.5 dex. SSF-gM is mainly used to predict M giant spectra with 3520 < Teff < 4000K and -1.5 < [M/H] < 0.4 dex. SSF-dM is for generating M dwarf spectra with 3295 < Teff < 4040K, -1.0 < [M/H] < 0.1 dex. And SSF-B can predict B-type spectra with 9000 < Teff < 24000K and -5.2< MG < 1.5 mag. The accuracy of the predicted spectra is validated by comparing the flux of predicted spectra to those with same stellar parameters selected from the known spectral libraries, MILES and MaStar. The averaged difference of flux over optical wavelength between the predicted spectra and the corresponding ones in MILES and MaStar is less than 5%. More verification is conducted between the magnitudes calculated from the integration of the predicted spectra and the observations in PS1 and APASS bands with the same stellar parameters. No significant systematic difference is found between the predicted spectra and the photomatric observations. The uncertainty is 0.08mag in r band for SSF-gM when comparing with the stars with the same stellar parameters selected from PS1. And the uncertainty becomes 0.31mag in i band for SSF-dM when comparing with the stars with the same stellar parameters selected from APASS.

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W. Ji, C. Liu and B. Zhang
Tue, 18 Apr 23
46/80

Comments: 16 pages, 13 figures

New variable sources revealed by DECam toward the LMC: the first 15 deg2 [SSA]

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http://arxiv.org/abs/2304.08133


The Dark Energy Camera (DECam) is a sensitive, wide field instrument mounted at the prime focus of the 4 m V. Blanco Telescope in Chile. Beside its main objectives, i.e. understanding the growth and evolution of structures in the Universe, the camera offers the opportunity to observe a 3 deg2 field of view in one single pointing and, with an adequate cadence, to identify the variable sources contained. In this paper, we present the result of a DECam observational campaign toward the LMC and give a catalogue of the observed variable sources. We considered all the available DECam observations of the LMC, acquired during 32 nights over a period of two years (from February 2018 to January 2020), and set up a specific pipeline for detecting and characterizing variable sources in the observed fields. Here, we report on the first 15 deg2 in and around the LMC as observed by DECam, testing the capabilities of our pipeline. Since many of the observed fields cover a rather crowded region of the sky, we adopted the ISIS subtraction package which, even in these conditions, can detect variables at a very low signal to noise ratio. All the potentially identified variable sources were then analyzed and each light curve tested for periodicity by using the Lomb-Scargle and Schwarzenberg-Czerny algorithms. Furthermore, we classified the identified sources by using the UPSILoN neural network. This analysis allowed us to find 70 981 variable stars, 1266 of which were previously unknown. We estimated the period of the variables and compared it with the available values in the catalogues. Moreover, for the 1266 newly detected objects, an attempted classification based on light curve analysis is presented.

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A. Franco, A. Nucita, F. Paolis, et. al.
Tue, 18 Apr 23
51/80

Comments: 11 pages, 7 figures

Probing the solar interior with lensed gravitational waves from known pulsars [SSA]

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http://arxiv.org/abs/2304.08220


When gravitational waves (GWs) from a spinning neutron star arrive from behind the Sun, they are subjected to gravitational lensing that imprints a frequency-dependent modulation on the waveform. This modulation traces the projected solar density and gravitational potential along the path as the Sun passes in front of the neutron star. We calculate how accurately the solar density profile can be extracted from the lensed GWs using a Fisher analysis. For this purpose, we selected three promising candidates (the highly spinning pulsars J1022+1001, J1730-2304, and J1745-23) from the pulsar catalog of the Australia Telescope National Facility. The lensing signature can be measured with $3 \sigma$ confidence when the signal-to-noise ratio (SNR) of the GW detection reaches $100 \, (f/300 {\rm Hz})^{-1}$ over a one-year observation period (where $f$ is the GW frequency). The solar density profile can be plotted as a function of radius when the SNR improves to $\gtrsim 10^4$.

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R. Takahashi, S. Morisaki and T. Suyama
Tue, 18 Apr 23
56/80

Comments: 12 pages, 12 figures; submitted to ApJ; a numerical code of the amplification factor for solar lensing is available at this http URL

Evidence for Misalignment Between Debris Disks and Their Host Stars [EPA]

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http://arxiv.org/abs/2304.07446


We place lower limits on the obliquities between debris disks and their host stars for 31 systems by comparing their disk and stellar inclinations. While previous studies did not find evidence for misalignment, we identify 6 systems with minimum obliquities falling between ~30{\deg}-60{\deg}, indicating that debris disks can be significantly misaligned with their stars. These high-obliquity systems span a wide range of stellar parameters with spectral types K through A. Previous works have argued that stars with masses below 1.2 $M_\odot$ (spectral types of ~F6) have magnetic fields strong enough to realign their rotation axes with the surrounding disk via magnetic warping; given that we observe high obliquities for relatively low-mass stars, magnetic warping alone is likely not responsible for the observed misalignment. Yet, chaotic accretion is expected to result in misalignments of ~20{\deg} at most and cannot explain the larger obliquities found in this work. While it remains unclear how primordial misalignment might occur and what role it plays in determining the spin-orbit alignment of planets, future work expanding this sample is critical towards understanding the mechanisms that shape these high-obliquity systems.

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S. Hurt and M. MacGregor
Tue, 18 Apr 23
57/80

Comments: Accepted to The Astrophysical Journal (ApJ)

Detection of magnetic galactic binaries in quasi-circular orbit with LISA [HEAP]

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http://arxiv.org/abs/2304.07294


Laser Interferometer Space Antenna (LISA) will observe gravitational waves from galactic binaries (GBs) of white dwarfs or neutron stars. Some of these objects are among the most magnetic astrophysical objects in the Universe. Magnetism, by secularly disrupting the orbit, can eventually affect the gravitational waves emission and could then be potentially detected and characterized after several years of observations by LISA. Currently, the data processing pipeline of the LISA Data Challenge (LDC) for GBs does not consider either magnetism or eccentricity. Recently, it was shown [Bourgoin et al. PRD 105, 124042 (2022)] that magnetism induces a shift on the gravitational wave frequencies. Additionally, it was argued that, if the binary’s orbit is eccentric, the presence of magnetism could be detected by LISA. In this work, we explore the consequences of a future data analysis conducted on quasi-circular and magnetic GB systems using the current LDC tools. We first show that a single eccentric GB can be interpreted as several GBs and this can eventually bias population studies deduced from LISA’s future catalog. Then, we confirm that for quasi-circular orbits, the secular magnetic energy of the system can be inferred if the signal-to-noise ratio of the second harmonic is high enough to be detected by traditional quasi-monochromatic source searching algorithms. LISA observations could therefore bring new insights on the nature and origin of magnetic fields in white dwarfs or neutron stars.

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E. Savalle, A. Bourgoin, C. Poncin-Lafitte, et. al.
Tue, 18 Apr 23
60/80

Comments: 18 pages, 6 figures

Mapping the distribution of OB stars and associations in Auriga [SSA]

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http://arxiv.org/abs/2304.08370


OB associations are important probes of recent star formation and Galactic structure. In this study, we focus on the Auriga constellation, an important region of star formation due to its numerous young stars, star-forming regions and open clusters. We show using \textit{Gaia} data that its two previously documented OB associations, Aur OB1 and OB2, are too extended in proper motion and distance to be genuine associations, encouraging us to revisit the census of OB associations in Auriga with modern techniques. We identify 5617 candidate OB stars across the region using photometry, astrometry and our SED fitting code, grouping these into 5 high-confidence OB associations using HDBSCAN. Three of these are replacements to the historical pair of associations – Aur OB2 is divided between a foreground and a background association – while the other two associations are completely new. We connect these OB associations to the surrounding open clusters and star-forming regions, analyse them physically and kinematically, constraining their ages through a combination of 3D kinematic traceback, the position of their members in the HR diagram and their connection to clusters of known age. Four of these OB associations are expanding, with kinematic ages up to a few tens of Myr. Finally, we identify an age gradient in the region spanning several associations that coincides with the motion of the Perseus spiral arm over the last $\sim$20 Myr across the field of view.

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A. Quintana, N. Wright and R. Jeffries
Tue, 18 Apr 23
63/80

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

MASTER OT J055845.55+391533.4: SU UMa star with a dip and long rebrightening [SSA]

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http://arxiv.org/abs/2304.07695


We analyzed Asteroid Terrestrial-impact Last Alert System (ATLAS), Zwicky Transient Facility (ZTF) and All-Sky Automated Survey for Supernovae (ASAS-SN) data of MASTER OT J055845.55+391533.4 and found that this object repeats superoutburst with a dip in the middle of the outburst followed by long and sometimes oscillating rebrightening, just like a WZ Sge-type dwarf nova or an AM CVn-type object. The mean supercycle was 298(8) d, too short for a WZ Sge star, but with only a few normal outbursts. We also observed the 2023 February-March superoutburst and established the superhump period of 0.05509(2) d. This period appears to exclude the possibility of an AM CVn star. Although the 2023 observations could not detect superhumps after the dip, the 2014, 2016 and 2021 data seem to suggest that low-amplitude superhumps were present during the rebrightening phase. We note that a dip during a superoutburst is a feature common to the unusual SU UMa-type dwarf nova MASTER OT J172758.09+380021.5 during some of its superoutbursts. These objects may comprise a new class of rebrightening phenomenon in SU UMa-type dwarf novae.

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T. Kato, H. Itoh, T. Vanmunster, et. al.
Tue, 18 Apr 23
64/80

Comments: 15 pages, 8 figures, VSOLJ Variable Star Bulletin No. 113

Far-infrared line emission from the outer Galaxy cluster Gy 3-7 with SOFIA/FIFI-LS: Physical conditions and UV fields [GA]

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http://arxiv.org/abs/2304.08127


(abridged) Far-infrared (FIR) line emission provides key information about the gas cooling and heating due to shocks and UV radiation associated with the early stages of star formation. Gas cooling via FIR lines might, however, depend on metallicity. We aim to quantify the FIR line emission and determine the spatial distribution of the CO rotational temperature, ultraviolet (UV) radiation field, and H2 number density toward the embedded cluster Gy 3-7 in the CMa-l224 star-forming region, whose metallicity is expected to be intermediate between that of the LMC and the Solar neighborhood. By comparing the total luminosities of CO and [O I] toward Gy 3-7 with values found for low- and high-mass protostars extending over a broad range of metallicities, we also aim to identify the possible effects of metallicity on the FIR line cooling within our Galaxy. We studied SOFIA/FIFI-LS spectra of Gy 3-7 covering several FIR lines. The spatial extent of CO high-J (J>14) emission resembles that of the elongated 160 um continuum emission detected with Herschel. The CO transitions from J=14-13 to J=16-15 are detected throughout the cluster and show a median rotational temperature of 170+/-30 K on Boltzmann diagrams. Comparisons to other protostars observed with Herschel show a good agreement with intermediate-mass sources in the inner Galaxy. Assuming an origin of the [O I] and high-J CO emission in UV-irradiated C-shocks, we obtained pre-shock H2 number densities of 10^4-5 cm-3 and UV radiation field strengths of 0.1-10 Habing fields. Far-IR line observations reveal ongoing star formation in Gy 3-7, dominated by intermediate-mass Class 0/I young stellar objects. The ratio of molecular-to-atomic far-IR line emission shows a decreasing trend with bolometric luminosities of the protostars. However, it does not indicate that the low-metallicity has an impact on the line cooling in Gy 3-7.

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N. Le, A. Karska, M. Figueira, et. al.
Tue, 18 Apr 23
71/80

Comments: 26 pages, 23 figures

GREX-PLUS Science Book [CEA]

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http://arxiv.org/abs/2304.08104


GREX-PLUS (Galaxy Reionization EXplorer and PLanetary Universe Spectrometer) is a mission candidate for a JAXA’s strategic L-class mission to be launched in the 2030s. Its primary sciences are two-fold: galaxy formation and evolution and planetary system formation and evolution. The GREX-PLUS spacecraft will carry a 1.2 m primary mirror aperture telescope cooled down to 50 K. The two science instruments will be onboard: a wide-field camera in the 2-8 $\mu$m wavelength band and a high resolution spectrometer with a wavelength resolution of 30,000 in the 10-18 $\mu$m band. The GREX-PLUS wide-field camera aims to detect the first generation of galaxies at redshift $z>15$. The GREX-PLUS high resolution spectrometer aims to identify the location of the water “snow line” in proto-planetary disks. Both instruments will provide unique data sets for a broad range of scientific topics including galaxy mass assembly, origin of supermassive blackholes, infrared background radiation, molecular spectroscopy in the interstellar medium, transit spectroscopy for exoplanet atmosphere, planetary atmosphere in the Solar system, and so on.

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G. Team, A. Inoue, Y. Harikane, et. al.
Tue, 18 Apr 23
77/80

Comments: This document is the first version of a collection of scientific themes which can be achieved with GREX-PLUS. Each section in Chapters 2 and 3 is based on the presentation at the GREX-PLUS Science Workshop held on 24-25 March, 2022 at Waseda University

The Gaia-ESO Survey: homogenisation of stellar parameters and elemental abundances [SSA]

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http://arxiv.org/abs/2304.07720


The Gaia-ESO Survey is a public spectroscopic survey that has targeted $\gtrsim10^5$ stars covering all major components of the Milky Way from the end of 2011 to 2018, delivering its public final release in May 2022. Unlike other spectroscopic surveys, Gaia-ESO is the only survey that observed stars across all spectral types with dedicated, specialised analyses: from O ($T_\mathrm{eff} \sim 30,000-52,000$~K) all the way to K-M ($\gtrsim$3,500~K). The physics throughout these stellar regimes varies significantly, which has previously prohibited any detailed comparisons between stars of significantly different type. In the final data release (internal data release 6) of the Gaia-ESO Survey, we provide the final database containing a large number of products such as radial velocities, stellar parameters and elemental abundances, rotational velocity, and also, e.g., activity and accretion indicators in young stars and membership probability in star clusters for more than 114,000 stars. The spectral analysis is coordinated by a number of Working Groups (WGs) within the Survey, which specialise in the various stellar samples. Common targets are analysed across WGs to allow for comparisons (and calibrations) amongst instrumental setups and spectral types. Here we describe the procedures employed to ensure all Survey results are placed on a common scale to arrive at a single set of recommended results for all Survey collaborators to use. We also present some general quality and consistency checks performed over all Survey results.

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A. Hourihane, P. Francois, C. Worley, et. al.
Tue, 18 Apr 23
78/80

Comments: A&A accepted, minor revision, 36 pages, 38 figures

A statistical model of stellar variability. I. FENRIR: a physics-based model of stellar activity, and its fast Gaussian process approximation [SSA]

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http://arxiv.org/abs/2304.08489


The detection of terrestrial planets by radial velocity and photometry is hindered by the presence of stellar signals. Those are often modeled as stationary Gaussian processes, whose kernels are based on qualitative considerations, which do not fully leverage the existing physical understanding of stars. Our aim is to build a formalism which allows to transfer the knowledge of stellar activity into practical data analysis methods. In particular, we aim at obtaining kernels with physical parameters. This has two purposes: better modelling signals of stellar origin to find smaller exoplanets, and extracting information about the star from the statistical properties of the data. We consider several observational channels such as photometry, radial velocity, activity indicators, and build a model called FENRIR to represent their stochastic variations due to stellar surface inhomogeneities. We compute analytically the covariance of this multi-channel stochastic process, and implement it in the S+LEAF framework to reduce the cost of likelihood evaluations from $O(N^3)$ to $O(N)$. We also compute analytically higher order cumulants of our FENRIR model, which quantify its non-Gaussianity. We obtain a fast Gaussian process framework with physical parameters, which we apply to the HARPS-N and SORCE observations of the Sun, and constrain a solar inclination compatible with the viewing geometry. We then discuss the application of our formalism to granulation. We exhibit non-Gaussianity in solar HARPS radial velocities, and argue that information is lost when stellar activity signals are assumed to be Gaussian. We finally discuss the origin of phase shifts between RVs and indicators, and how to build relevant activity indicators. We provide an open-source implementation of the FENRIR Gaussian process model with a Python interface.

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N. Hara and J. Delisle
Tue, 18 Apr 23
79/80

Comments: Submitted to Astronomy \& Astrophysics

Physical and chemical complexity in high-mass star-forming regions with ALMA. I. Overview and evolutionary trends of physical properties [GA]

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http://arxiv.org/abs/2304.07237


In this study, we investigate how physical properties, such as the density and temperature profiles, evolve on core scales through the evolutionary sequence during high-mass star formation ranging from protostars in cold infrared dark clouds to evolved UCHII regions. We observed 11 high-mass star-forming regions with ALMA at 3 mm wavelengths. Based on the 3 mm continuum morphology and recombination line emission, tracing locations with free-free (ff) emission, the fragmented cores analyzed in this study are classified into either dust or dust+ff cores. In addition, we resolve three cometary UCHII regions with extended 3 mm emission that is dominated by free-free emission. The temperature structure and radial profiles (T~r^-q ) are determined by modeling molecular emission of CH3CN and CH313CN with XCLASS and by using the HCN-to- HNC intensity ratio as probes for the gas kinetic temperature. The density profiles (n~r^-p ) are estimated from the 3 mm continuum visibility profiles. The masses M and H2 column densities N(H2) are then calculated from the 3 mm dust continuum emission. Results. We find a large spread in mass and peak H2 column density in the detected sources ranging from 0.1-150 Msun and 10^23 – 10^26 cm-2 , respectively. Including the results of the CORE and CORE-extension studies (Gieser et al. 2021, 2022) to increase the sample size, we find evolutionary trends on core scales for the temperature power-~law index q increasing from 0.1 to 0.7 from infrared dark clouds to UCHII regions, while for the the density power-law index p on core scales, we do not find strong evidence for an evolutionary trend. However, we find that on the larger clump scales throughout these evolutionary phases the density profile flattens from p = 2.2 to p = 1.2. (abridged)

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C. Gieser, H. Beuther, D. Semenov, et. al.
Mon, 17 Apr 23
1/51

Comments: 21 pages, 10 figures, submitted to A&A

Diffusion Coefficients of $^{56}$Fe in C-O and O-Ne White Dwarfs [SSA]

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http://arxiv.org/abs/2304.07228


The diffusion coefficients of neutron rich nuclei in crystallizing white dwarf (WD) stars are essential microphysics input for modeling the evolution of the composition profile. Recently, molecular dynamics simulations have been used to compute diffusion coefficients for realistic mixtures of C-O and O-Ne WDs with many trace nuclides that could be important sedimentary heat sources such as $^{22}$Ne, $^{23}$Na, $^{25}$Mg, and $^{27}$Mg. In this brief note, I repeat these simulations but now include $^{56}$Fe. I find that for the large charge ratios involved in these mixtures the empirical law developed in our earlier work tends to under-predict diffusion coefficients in the moderately coupled regime by 30 to 40 percent. As this formalism is presently implemented in the stellar evolution code MESA, it is important for authors studying mixtures containing heavy nuclides like $^{56}$Fe to be aware of these systematics. However, the impact on astrophysics is expected to be small.

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M. Caplan
Mon, 17 Apr 23
6/51

Comments: 3 pages, 1 figure, submitted to RNAAS

Investigating Gaia EDR3 parallax systematics using asteroseismology of Cool Giant Stars observed by Kepler, K2, and TESS I. Asteroseismic distances to 12,500 red-giant stars [SSA]

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http://arxiv.org/abs/2304.07158


Gaia EDR3 has provided unprecedented data that generate a lot of interest in the astrophysical community, despite the fact that systematics affect the reported parallaxes at the level of ~ 10 muas. Independent distance measurements are available from asteroseismology of red-giant stars with measurable parallaxes, whose magnitude and colour ranges more closely reflect those of other stars of interest. In this paper, we determine distances to nearly 12,500 red-giant branch and red clump stars observed by Kepler, K2, and TESS. This is done via a grid-based modelling method, where global asteroseismic observables, constraints on the photospheric chemical composition, and on the unreddened photometry are used as observational inputs. This large catalogue of asteroseismic distances allows us to provide a first comparison with Gaia EDR3 parallaxes. Offset values estimated with asteroseismology show no clear trend with ecliptic latitude or magnitude, and the trend whereby they increase (in absolute terms) as we move towards redder colours is dominated by the brightest stars. The correction model proposed by Lindegren et al. (2021) is not suitable for all the fields considered in this study. We find a good agreement between asteroseismic results and model predictions of the red clump magnitude. We discuss possible trends with the Gaia scan law statistics, and show that two magnitude regimes exist where either asteroseismology or Gaia provides the best precision in parallax.

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S. Khan, A. Miglio, E. Willett, et. al.
Mon, 17 Apr 23
11/51

Comments: 11 pages, 8 figures, Accepted for publication in A&A

Near-Core Acoustic Glitches are Not Oscillatory: Consequences for Asteroseismic Probes of Convective Boundary Mixing [SSA]

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http://arxiv.org/abs/2304.06770


Asteroseismology has been used extensively in recent years to study the interior structure and physical processes of main sequence stars. We consider prospects for using pressure modes (p-modes) near the frequency of maximum oscillation power to probe the structure of the near-core layers of main sequence stars with convective cores by constructing stellar model tracks. Within our mass range of interest, the inner turning point of p modes as determined by the JWKB approximation evolves in two distinct phases during the main sequence, implying a sudden loss of near-core sensitivity during the discontinuous transition between the two phases. However, we also employ non-JWKB asymptotic analysis to derive a contrasting set of expressions for the effects that these structural properties will have on the mode frequencies, which do not encode any such transition. We show analytically that a sufficiently near-core perturbation to the stellar structure results in non-oscillatory, degree-dependent perturbations to the star’s oscillation mode frequencies, contrasting with the case of an outer glitch. We also demonstrate numerically that these near-core acoustic glitches exhibit strong angular degree dependence, even at low degree, agreeing with the non-JWKB analysis, rather than the degree-independent oscillations which emerge from JWKB analyses. These properties have important implications for using p-modes to study near-core mixing processes for intermediate-mass stars on the main sequence, as well as for the interpretation of near-center acoustic glitches in other astrophysical configurations, such as red giants.

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C. Lindsay, J. Ong and S. Basu
Mon, 17 Apr 23
18/51

Comments: 14 pages, 5 figures, Accepted for publication in ApJ: April 12, 2023

Solar P-angle Alignment in GONG Dopplergrams [SSA]

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http://arxiv.org/abs/2304.07192


In helioseismic studies, an observational parameter of primary concern is the P-angle, the angle along which lies the solar axis of rotation for a given image. For the six observing sites employed by The Global Oscillation Network Group (GONG), this angle acts additionally as a marker of relative image orientation, allowing concurrent images to be precisely aligned and merged to provide the highest possible quality data. In this report, we present and investigate two methods of determining the P-angle via the rotational signature embedded in solar Dopplergram images by examining the large-scale structure of the observed velocity field. As with other studies, we find that the Dopplergram produces a time-varying ‘P-angle’ signature according to the presentation of various physical phenomena across the solar surface, but with the potential for sub-degree identification of the axis of rotation. However, close agreement between separate P-angle-finding techniques also reveals current limitations to P-angle determination that are imposed by the calibration state of the GONG-site Dopplergrams, leaving these P-angle-finding methods for GONG with errors on the scale of less than a degree between two site.

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A. Hughes, I. Gonzalez-Hernandez, S. McManus, et. al.
Mon, 17 Apr 23
22/51

Comments: 36 pages, 32 figures

A benchmark study of atomic models for the transition region against quiet Sun observations [SSA]

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http://arxiv.org/abs/2304.07038


The use of the coronal approximation to model line emission from the solar transition region has led to discrepancies with observations over many years, particularly for Li- and Na-like ions. Studies have shown that a number of atomic processes are required to improve the modelling for this region, including the effects of high densities, solar radiation and charge transfer on ion formation. Other non-equilibrium processes, such as time dependent ionisation and radiative transfer, are also expected to play a role. A set of models which include the three relevant atomic processes listed above in ionisation equilibrium has recently been built. These new results cover the main elements observed in the transition region. To assess the effectiveness of the results, the present work predicts spectral line intensities using differential emission measure modelling. Although limited in some respects, this differential emission measure modelling does give a good indication of the impact of the new atomic calculations. The results are compared to predictions of the coronal approximation and to observations of the average, quiet Sun from published literature. Significant improvements are seen for the line emission from Li- and Na-like ions, inter-combination lines and many other lines. From this study, an assessment is made of how far down into the solar atmosphere the coronal approximation can be applied, and the range over which the new atomic models are valid.

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R. Dufresne, G. Zanna and H. Mason
Mon, 17 Apr 23
23/51

Comments: Accepted by MNRAS, 16 pages, 3 figures

Optical characteristics and capabilities of the successive versions of Meudon and Haute Provence H$α$ heliographs (1954-2004) [IMA]

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http://arxiv.org/abs/2304.07055


H$\alpha$ heliographs are imaging instruments designed to produce monochromatic images of the solar chromosphere at fast cadence (60 s or less). They are designed to monitor efficiently dynamic phenomena of solar activity, such as flares or material ejections. Meudon and Haute Provence observatories started systematic observations in the frame of the International Geophysical Year (1957) with Lyot filters. This technology evolved several times until 1985 with tunable filters allowing to observe alternatively the line wings and core (variable wavelength). More than 6 million images were produced during 50 years, mostly on 35 mm films (catalogs are available on-line). We present in this paper the optical characteristics and the capabilities of the successive versions of the H$\alpha$ heliographs in operation between 1954 and 2004, and describe briefly the new heliograph (MeteoSpace) which will be commissioned in 2023 at Calern observatory.

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J. Malherbe
Mon, 17 Apr 23
25/51

Comments: N/A