arXiv subjects

Luca Casagrande

Publications and source records attributed to Luca Casagrande.

At least 19 recordsLinked to original sources

arXiv2026

Dynamically driven collapse of a thermally stable accretion disk in a nova-like system

While standard disk instability theory predicts thermal-steady, outburst-free disks in nova-like variables due to their high mass transfer rates, mass transfer variations are prevailingly invoked to explain the occasional flaring/fading phenomena observed in these systems. Here we report the observational evidence for a dynamical collapse of a thermally stable accretion disk, captured serendipitously by TESS during a fading episode of the VY Scl-type nova-like system MASTER OT J072703.91-631952.8, and traced by the emergence of an unusual negative superhump that evolves toward its orbital frequency. Simultaneously, the system underwent an anomalous eruptive event featuring a remarkably symmetric 45-day light-curve profile, indicative of a mild energy-release mechanism fundamentally distinct from documented eruptive events in cataclysmic variables. Notably, the concurrence of the eruption and the disk collapse is difficult to reconcile with the paradigm of mass transfer variations: the eruption implies enhanced mass transfer, whereas the disk collapse indicates a decline. The morphological disk evolution over $\sim 700$ days, characterized by both negative and positive superhumps, indicates a transition from a circular disk to an eccentric disk, followed by a tilted state and ultimately a minimal disk configuration. This evolutionary sequence provides evidence for a previously unrecognized dynamics-driven cycle operating in the thermally stable accretion disk of a VY Scl-type nova-like star.

astro-ph.SR↗

arXiv2026

Collective deformation of anisotropic particles with internal pulsation

Capturing the emergence of deformation waves in contractile living tissues is a challenge that has recently been tackled with models of actively deformable particles. Inspired by the anisotropic deformation of cardiomyocytes in cardiac tissues, we examine how the pulsation of elliptical particles affects their collective properties in dense assemblies. We introduce two types of deformation where the eccentricity of each particle is subject to a periodic drive, and examine the interplay between nematic order and synchronized deformation via a systematic phase diagram. We derive a hydrodynamic description through a coarse-graining procedure, and show that it qualitatively captures the main collective states of the microscopic dynamics. Overall, our model provides key insights into how an active anisotropic deformation yields waves that self-organize into various dynamical patterns.

cond-mat.soft↗

arXiv2026

Detailed Abundance Determination of Metal-Poor Stars with X-Shooter II. - Chemically Disentangling the Halo, Disk and GSE

We present a detailed chemical analysis of seven extremely metal-poor (EMP) star candidates observed with X-Shooter, combining them with 16 EMP candidates from Paper I. We measured abundances for 16 elements, showing excellent agreement with previously published results. The sample was further extended using high-resolution literature data for 315 metal-poor stars. The full sample was then kinematically separated into prograde disk, retrograde disk, Gaia-Sausage Enceladus (GSE) and halo classifications. Combining dynamics with chemistry, we demonstrate that the prograde disk exhibits a distinct negative linear trend in [Sc/Mg] with increasing metallicity, with a slope of -0.6 dex per dex. This contrasts with the halo trend at -0.04 dex per dex, a difference significant at the 3.95$σ$ level. Within the metallicity range -4.2 $\leq$ [Fe/H] $\leq$ -1.9, the prograde disk trend is driven by low [Mg/Fe] at lower metallicities, along with low [Sc/Fe] at higher metallicities. This could be due to reduced early Mg enrichment in the progenitor prograde disk, followed by subsequent Mg enrichment, possibly associated with a later gas accretion event. However, the physical origin of the higher-metallicity Sc depletion remains unexplained by current nucleosynthesis models. The result remains significant at the >3$σ$ level across kinematic classifications derived from a different Galactic potential. Additionally, we also identified an r-I star with enhanced Ti, moderately-enhanced Sc, and depleted in C (unrelated to its evolutionary state). These abundances suggest a massive jet-induced hypernova progenitor, though a measurement of Zn is needed to verify this.

astro-ph.GA↗

arXiv2026

Topology of pulsating active matter: Defect asymmetry controls emergent motility

In pulsating active matter, topological defects are motile despite the absence of any macroscopic flows and microscopic self-propulsion. We reveal that this motility arises from a ratchet effect: the mechanochemical coupling between local oscillations and repulsive interactions breaks both spatial and time-reversal symmetries, thus leading asymmetric rotating defects to drift under fluctuations. This mechanism regulates a crossover between spiral waves connecting slow defects and fiber-like waves connecting fast defects, in analogy with the onset of heart rhythm disorder in cardiac tissues. We rationalize this crossover in terms of a fluctuating hydrodynamics that captures how motile defects spontaneously nucleate and move within an ordered background.

cond-mat.soft↗

arXiv2026

GASTAG evolutionary tracks and isochrones from coupled 1D and 3D models: Systematic temperature offsets in red giants

Models of stellar structure and evolution describe the global and internal properties of stars throughout their lifetimes and are indispensable for studies of stellar clusters and Galactic evolution. However, most 1D evolutionary calculations rely on simplified treatment of convection, resulting in inaccurate near-surface structures and non-negligible uncertainties in the predicted fundamental parameters of low-mass stars. In a series of previous works, a novel approach was developed to couple 1D stellar interior models with 3D model atmospheres throughout the evolutionary calculation. This 1D-3D coupling method makes predicted stellar properties effectively independent of the mixing-length parameter. To expand this framework to ensemble studies of stars and age determinations of clusters, we present the GASTAG stellar evolutionary tracks and isochrones constructed using the 1D-3D coupling approach. Comparing effective temperatures from the APOGEE-Kepler catalog with GASTAG predictions, we find the theoretical temperatures are cooler by about 70 K near solar metallicity. Our isochrones are compared with observed color-magnitude diagrams of star clusters spanning from $\rm [Fe/H] = 0.3$ to $-1.9$. In all cases, the synthesized and observed diagrams agree excellently in the main-sequence, turn-off, and subgiant regions, while isochrones predict systematically cooler red giant branches. Taking these independent findings together reveals that the temperature mismatch is most likely due to deficiencies in stellar models. Because GASTAG is constructed using a method that substantially reduces uncertainties associated with surface boundary conditions and the mixing-length parameter, the difference between modeling and observation can be more confidently attributed to other ingredients in the models, such as $α$-element abundances or uncertainties in low-temperature opacities.

astro-ph.SR↗

arXiv2026

Empirical colour--effective temperature relations in the SDSS system from IRFM temperatures of GALAH and APOGEE stars

Reliable estimates of stellar effective temperature ($T_{\mathrm {eff}}$) are fundamental to stellar population studies and Galactic astrophysics. However, the majority of stars observed in modern large-scale photometric surveys lack spectroscopic measurements, making empirical colour--$T_{\mathrm {eff}}$ relations essential tools. In this work, we present updated empirical colour--$T_{\mathrm {eff}}$ calibrations based on Sloan Digital Sky Survey (SDSS) $ugriz$ photometry combined with 2MASS $JHK_{\mathrm s}$ data. Effective temperatures are determined on a homogeneous InfraRed Flux Method (IRFM) scale using a combined sample of 3902 GALAH and 2535 APOGEE stars with high-quality photometry and well-characterised atmospheric parameters. Using this dataset, we establish empirical relations between $T_{\mathrm {eff}}$ and colour indices constructed from SDSS and 2MASS combinations. We provide both colour--metallicity--$T_{\mathrm {eff}}$ and colour--$T_{\mathrm {eff}}$ relations for dwarfs and giants. The calibrations are derived using low-order polynomial models with iterative $3σ$ clipping. Their performance depends on the adopted colour index, with long-baseline colours such as $(g-K_{\mathrm s})_0$ and $(g-z)_0$ achieving internal precisions of $\sim$30--50~K. Comparisons with previous calibrations show general agreement, with differences attributable to sample selection, photometric zero-points, and functional form. The resulting relations provide a homogeneous and internally consistent framework for estimating $T_{\mathrm {eff}}$ from SDSS and 2MASS photometry alone, and are well suited for application to large photometric surveys lacking spectroscopic information.

astro-ph.SR↗

arXiv2026

Recalibration of SDSS photometric zero-points based on the InfraRed Flux Method temperature scale

Accurate photometric zero-points are essential for translating observed magnitudes into physical fluxes, from comparing with models to ensuring consistency across surveys. We determine the zero-points needed to place the Sloan Digital Sky Survey (SDSS) $ugriz$ system on its nominal AB definition, by exploiting the sensitivity of the Infrared Flux Method (IRFM) to broadband flux calibration. Using benchmark effective temperatures for over 6,000 FGK-type stars, we invert the method to identify the zero-point corrections required for SDSS photometry to reproduce the adopted temperature scale. The $r$ band is found to be very well standardized, while the $i$ and $z$ bands show offsets of a few hundredths of a magnitude, consistent with previous studies. We also find a small offset in the $g$ band. The largest discrepancy occurs in the $u$ band, where the derived offset depends strongly on the adopted filter transmission curves, in particular whether one uses the original definition commonly adopted in the literature or the updated measurements that account for the presence of a red leak. This effect introduces a colour-dependent zero-point offset that becomes apparent when using a sample of late-type stars. Independent comparisons with CALSPEC spectrophotometric standards and Gaia XP spectra broadly support the offsets derived from the IRFM analysis. Our results provide a revised set of SDSS zero-points anchored to the IRFM temperature scale and demonstrate that large stellar samples can be used to constrain photometric calibration. The methodology presented here offers a complementary approach to traditional spectrophotometric calibration and may prove useful for future large-scale surveys.

astro-ph.IM↗

arXiv2026

High-fidelity stellar extinction with Gaia and APOGEE -- I. The method and a new extinction curve

The scarcity of high-fidelity extinction measurements remains a bottleneck in deriving accurate stellar properties from Gaia parallaxes. In this work, we aim to derive precision extinction estimates for APOGEE DR19 stars, establishing a new benchmark for Galactic stellar population studies. We first determine reddening by comparing observed colorsr, etrieved from photometric surveys or standardized synthetic magnitudes from Gaia BP/RP spectra, to intrinsic colors predicted via an XGBoost model. The model is trained on minimally reddened stars to infer intrinsic colors and their associated uncertainties, using APOGEE stellar parameters (Teff, logg, [Fe/H], and [alpha/Fe]). The derived reddening values are then converted into extinctions using an anchor ratio of A_BP / A_RP = 1.694 +/- 0.004, derived from red-clump-like stars. Here, we provide extinction measurements in 39 filters across 10 photometric systems and introduce a new empirical extinction curve optimized for broadband passbands. Our extinction estimates (Av) outperform existing results (Bayestar19, StarHorse, SEDEX), achieving a typical precision of 0.03 mag in Av. Notably, we identify systematic deviations of up to 30% between monochromatic and passband-integrated extinction ratios at wavelengths greater than 700 nm. This result highlights the necessity of adopting passband-specific coefficients when correcting extinction to derive stellar parameters. The derived extinction and reddening data are available to the community for download through Zenodo.

astro-ph.SR↗

arXiv2026

Detailed Abundance Determination of Metal-Poor Stars with X-Shooter I. Unusual Chemistry in Halo Stars

We present a detailed chemical analysis study of 16 candidate metal-poor stars, previously identified with 2dF + AAOmega, using X-Shooter spectra and the Korg 1D local thermodynamic equilibrium spectral synthesis code. We confirm the earlier metallicity estimates and reveal six extremely metal-poor ([Fe/H] $< -3$) stars in the current sample. Two of these stars, including the most metal poor at [Fe/H] = $-3.89 \pm 0.07$, are kinematically associated with the Gaia-Sausage-Enceladus (GSE) accretion event, increasing the number of known GSE stars with [Fe/H] $< -3.5$ to eight. From the X-Shooter spectra we determine abundances for 16 elements, with the element-to-iron abundance ratios generally consistent with high-resolution studies of Galactic halo stars. Within the sample, we identify three peculiar stars: the first is a GSE nitrogen enhanced metal-poor ([N/Fe] $= 1.60 \pm 0.10$ and [C/Fe] $= 0.23 \pm 0.08$) star with unusually high Na ([Na/Fe] $= 2.26 \pm 0.07$) and Li (A(Li)$_{\rm 3DNLTE} = 1.90 \pm 0.08$) abundances, but lacking enhancements in [Al/Fe] or [Mg/Fe]. The second is a halo r-II star significantly enhanced in Sr ([Sr/Ba] $= 0.39 \pm 0.08$), suggesting mixture of r-process and s-process enrichment, uncommon for r-II stars. Whilst the third is a halo star very depleted in N ([N/Fe] $< -1.11$), with low C ([C/Fe] $= -0.33 \pm 0.08$) and otherwise 'normal' [X/Fe] abundances, suggesting enrichment with Type II supernova that proceeds enrichment from massive asymptotic giant branch stars. This study reveals the substantial degree of chemical diversity in the stellar populations which assembled the early Milky Way.

astro-ph.GA↗

arXiv2025

Rubin Data Preview 1: Extending the View of Unresolved Binary Stars in 47 Tucanae

Until now, the study of unresolved main sequence binary stars in globular clusters has been possible almost exclusively in their central regions with deep Hubble Space Telescope (HST) observations. We present the first detection of unresolved main-sequence binary stars in the outer field of 47 Tucanae using Rubin Observatory's Data Preview 1 (DP1). Our analysis exploits deep $i$ vs. $g-i$ colour-magnitude diagrams beyond the cluster's half-light radius, reaching almost to the tidal radius. The high-quality photometry allowed to identify unresolved binaries with mass ratios $q$ larger than 0.7. The derived binary fraction of $f_\mathrm{bin}(q>0.7) = 0.016 \pm 0.005$ stands in contrast to the significantly lower values in the cluster innermost regions, as measured from HST photometry. This result provides new empirical input for testing physical processes that drive the formation and evolution of binary stars in globular clusters. It also demonstrates Rubin's unique wide-field and high-precision photometric capabilities to address a broader range of outstanding questions in star cluster research. Future full data releases will enable to significantly expand the study of dense stellar systems across the Milky Way.

astro-ph.SR↗

arXiv2025

Asteroseismology of the G8 subgiant beta Aquilae with SONG-Tenerife, SONG-Australia and TESS

We present time-series radial velocities of the G8 subgiant star beta Aql obtained in 2022 and 2023 using SONG-Tenerife and, for the first time, SONG-Australia. We also analyse a sector of TESS photometry that overlapped with the 2022 SONG data. The resulting power spectrum clearly shows solar-like oscillations centred at 430 muHz. The TESS light curve shows the oscillations at lower signal-to-noise, reflecting the fact that photometric measurements are much more affected by the granulation background than are radial velocities. The simultaneous observations in velocity and photometry represent the best such measurements for any star apart from the Sun. They allowed us to measure the ratio between the bolometric photometric amplitude and the velocity amplitude to be 26.6 +/- 3.1 ppm/(m/s). We measured this ratio for the Sun from published SOHO data to be 19.5 +/- 0.7 ppm/(m/s) and, after accounting for the difference in effective temperatures of and the Sun, these values align with expectations. In both the Sun and beta Aql, the photometry-to-velocity ratio appears to be a function of frequency. We also measured the phase shift of the oscillations in beta Aql between SONG and TESS to be -113 +/- 7 deg, which agrees with the value for the Sun and also with a 3-D simulation of a star with similar properties to beta Aql. Importantly for exoplanet searches, we argue that simultaneous photometry can be used to predict the contribution of oscillations to radial velocities. We measured frequencies for 22 oscillation modes in beta Aql and carried out asteroseismic modelling, yielding an excellent fit to the frequencies. We derived accurate values for the mass and age, and were able to place quite strong constraints on the mixing-length parameter. Finally, we show that the oscillation properties of beta Aql are very similar to stars in the open cluster M67.

astro-ph.SR↗

arXiv2025

Cryoscope: A Cryogenic Infrared Survey Telescope in Antarctica

We present Cryoscope--a new 50 deg$^2$ field-of-view, 1.2 m aperture, $K_{dark}$ survey telescope to be located at Dome C, Antarctica. Cryoscope has an innovative optical-thermal design wherein the entire telescope is cryogenically cooled. Cryoscope also explores new detector technology to cost-effectively tile the full focal plane. Leveraging the dark Antarctic sky and minimizing telescope thermal emission, Cryoscope achieves unprecedented deep, wide, fast and red observations, matching and exceeding volumetric survey speeds from the Ultraviolet Explorer, Vera Rubin Observatory, Nancy Grace Roman Space Telescope, SPHEREx, and NEO Surveyor. By providing coverage beyond wavelengths of 2 $μ$m, we aim to create the most comprehensive dynamic movie of the most obscured reaches of the Universe. Cryoscope will be a dedicated discovery engine for electromagnetic emission from coalescing compact binaries, Earth-like exoplanets orbiting cold stars, and multiple facets of time-domain, stellar and solar system science. In this paper, we describe the scientific drivers and technical innovations for this new discovery engine operating in the $K_{dark}$ passband, why we choose to deploy it in Antarctica, and the status of a fifth-scale prototype designed as a Pathfinder to retire technological risks prior to full-scale implementation. We plan to deploy the Cryoscope Pathfinder to Dome C in December 2026 and the full-scale telescope by 2030.

astro-ph.IM↗

arXiv2025

C3PO IV: co-natal stars depleted in refractories are magnetically more active -- possible imprints of planets

Chemical abundance anomalies in twin stars have recently been considered tell-tale signs of interactions between stars and planets. While such signals are prevalent, their nature remains a subject of debate. On one hand, exoplanet formation may induce chemical depletion in host stars by locking up refractory elements. On the other hand, exoplanet engulfment can result in chemical enrichment, both processes potentially producing similar differential signals. In this study, we aim to observationally disentangle these processes by using the Ca II infrared triplet to measure the magnetic activity of 125 co-moving star pairs with high SNR, high-resolution spectra from the Magellan, Keck, and VLT telescopes. We find that co-natal star pairs in which the two stars exhibit significant chemical abundance differences also show differences in their magnetic activity, with stars depleted in refractories being magnetically more active. Furthermore, the strength of this correlation between differential chemical abundances and differential magnetic activity increases with condensation temperature. One possible explanation is that the chemical anomaly signature may be linked to planet formation, wherein refractory elements are locked into planets, and the host stars become more active due to more efficient contraction during the pre-main-sequence phase or star-planet tidal and magnetic interactions.

astro-ph.EP↗

arXiv2025

Internal Dynamics of Multiple Populations in 28 Galactic Globular Clusters: A Wide-Field study with Gaia and the Hubble Space Telescope

We present a detailed analysis of the internal dynamics of multiple stellar populations (MPs) in 28 Galactic Globular Clusters (GCs) across a wide field of view, extending from the innermost regions to the clusters' outskirts. Using astro-photometric catalogs from ground-based observations, Gaia, and the Hubble Space Telescope (HST), we identify first- (1P) and second-population (2P) stars, and study the internal dynamics of MPs using high-precision Gaia DR3 and HST proper motions. Our results reveal that while the 1P transitions from isotropy to slight tangential anisotropy toward the outer regions, 2P stars become increasingly radially anisotropic beyond the half-light radius. We also explore the connection between the dynamics of MPs and the clusters' structural and dynamical properties, finding statistically significant differences in the anisotropy profiles of dynamically young and non-relaxed clusters, particularly beyond the 1-2 half-light radii. In these regions, 1P stars transition from isotropic to slightly tangentially anisotropic motion, while 2P stars become more radially anisotropic. In contrast, dynamically older clusters, with mixed MPs, exhibit weaker relative differences. Furthermore, clusters with orbits closer to the Galactic center exhibit larger dynamical differences between 1P and 2P stars than those with larger peri-Galactic radii. These findings are consistent with a scenario where 2P stars form in a more centrally concentrated environment, where the interaction with the Milky Way tidal field plays a crucial role in the dynamical evolution of MPs, especially of 1P.

astro-ph.GA↗

arXiv2024

Survey of extended Main Sequence Turn-offs in Galactic Open Clusters: Stellar rotations from Gaia RVS spectra

The origin of extended main-sequence turn-offs (eMSTO) in star clusters younger than 2 Gyr still challenges our current understanding of stellar evolution. Exploiting data from Gaia Data Release 3 (DR3), we investigate eMSTOs in a large sample of 32 Galactic open clusters younger than 2.4 Gyr. We first validate Gaia rotational velocities from Radial Velocity Spectrometer (RVS) spectra by comparing them with literature values and assessing their correlation with magnetic activity measurements from LAMOST spectra. We detect a general positive correlation between turn-off color and projected stellar rotation, with slow-rotating stars predominantly found on the bluer side of the turn-off. Comparing our observations with theoretical models, we find that the eMSTO morphology is well-reproduced by a single population formed with a high rotation rate, and observed with rotation axis inclination ranging between 0$^\circ$ (pole-on) and 90$^\circ$ (edge-on). This contrasts with observations of Magellanic Clouds clusters, where a population of non-rotating stars appears to be ubiquitous in clusters younger than 700 Myr. However, we note that our interpretation, while successfully explaining the overall eMSTO morphology, cannot fully explain the observed projected rotational velocities. Additionally, two young clusters, NGC 3532 and NGC 2287, exhibit moderate evidence of a split main sequence in color and rotation, suggesting a possible small spread in the initial rotation rate. Finally, we advise caution in determining the ages of young clusters from non-rotating isochrones, as neglecting the effects of stellar rotation can impact the isochrone dating by up to factors of 5-20%.

astro-ph.GA↗

arXiv2024

The K2 Asteroseismic KEYSTONE sample of Dwarf and Subgiant Solar-Like Oscillators. I: Data and Asteroseismic parameters

The KEYSTONE project aims to enhance our understanding of solar-like oscillators by delivering a catalogue of global asteroseismic parameters (${Δν}$ and ${ν_{\rm max}}$) for 173 stars, comprising mainly dwarfs and subgiants, observed by the K2 mission in its short-cadence mode during campaigns 6-19. We derive atmospheric parameters and luminosities using spectroscopic data from TRES, astrometric data from $\textit{Gaia}$, and the infrared flux method (IRFM) for a comprehensive stellar characterisation. Asteroseismic parameters are robustly extracted using three independent methods, complemented by an iterative refinement of the spectroscopic analyses using seismic ${\log g}$ values to enhance parameter accuracy. Our analysis identifies new detections of solar-like oscillations in 159 stars, providing an important complement to already published results from previous campaigns. The catalogue provides homogeneously derived atmospheric parameters and luminosities for the majority of the sample. Comparison between spectroscopic ${T_{\rm eff}}$ and those obtained from the IRFM demonstrates excellent agreement. The iterative approach to spectroscopic analysis significantly enhances the accuracy of the stellar properties derived.

astro-ph.SR↗

arXiv2024

The GALAH survey: Tracing the Milky Way's formation and evolution through RR Lyrae stars

Stellar mergers and accretion events have been crucial in shaping the evolution of the Milky Way (MW). These events have been dynamically identified and chemically characterised using red giants and main-sequence stars. RR Lyrae (RRL) variables can play a crucial role in tracing the early formation of the MW since they are ubiquitous, old (t$\ge$10 Gyr) low-mass stars and accurate distance indicators. We exploited Data Release 3 of the GALAH survey to identify 78 field RRLs suitable for chemical analysis. Using synthetic spectra calculations, we determined atmospheric parameters and abundances of Fe, Mg, Ca, Y, and Ba. Most of our stars exhibit halo-like chemical compositions, with an iron peak around [Fe/H]$\approx -$1.40, and enhanced Ca and Mg content. Notably, we discovered a metal-rich tail, with [Fe/H] values ranging from $-$1 to approximately solar metallicity. This sub-group includes almost ~1/4 of the sample, it is characterised by thin disc kinematics and displays sub-solar $α$-element abundances, marginally consistent with the majority of the MW stars. Surprisingly, they differ distinctly from typical MW disc stars in terms of the s-process elements Y and Ba. We took advantage of similar data available in the literature and built a total sample of 535 field RRLs for which we estimated kinematical and dynamical properties. We found that metal-rich RRLs (1/3 of the sample) likely represent an old component of the MW thin disc. We also detected RRLs with retrograde orbits and provided preliminary associations with the Gaia-Sausage-Enceladus, Helmi, Sequoia, Sagittarius, and Thamnos stellar streams.

astro-ph.GA↗

arXiv2024

New Evidence of Binarity in Young α-Rich Turn-off and Subgiant Stars: Fast Rotation and Strong Magnetic Activity

Young α-rich (YAR) stars within the old Galactic thick disk exhibit a dual characteristic of relative youth determined with asteroseismology and abundance enhancement in α elements measured from high-resolution spectroscopy. The youth origin of YAR stars has been proposed to be binary evolution via mass transfer or stellar mergers. If that is the case, YAR stars should spin rapidly and thus be magnetically active, because they are mass and angular momentum gainers. In this study, to seek this binary footprint we select YAR stars on the main-sequence turn-off or the subgiant branch (MSTO-SGB) from APOGEE DR17, whose ages and projected rotation velocities (vsini) can be precisely measured. With APOGEE vsini and LAMOST spectra, we find that YAR stars are indeed fast rotators and magnetically active. In addition, we observe low [C/N] ratios and high Gaia RUWE in some YAR stars, suggesting that these MSTO-SGB stars probably have experienced mass transfer from red-giant companions. Our findings underscore that magnetic activity can serve as a valuable tool for probing the binary evolution for other chemically peculiar stars, such as red giants with lithium anomalies and carbon-enhanced metal-poor stars.

astro-ph.SR↗