arXiv subjects

László Molnár

Publications and source records attributed to László Molnár.

At least 19 recordsLinked to original sources

arXiv2026

Integrated Mass Loss for Very Metal-poor Stars: Asterosesimic Red Giant Masses of K2 Globular Cluster NGC 5897

Mass loss in low-mass stars during the red giant branch (RGB) and early asymptotic giant branch (EAGB) phases plays a key role in shaping stellar evolution, yet its dependence on stellar parameters such as metallicity remains poorly constrained, with observational studies yielding conflicting trends. We present the first asteroseismic analysis of RGB and EAGB stars in NGC 5897, the most distant and metal-poor globular cluster observed by the Kepler space telescope during the K2 mission. We detected solar-like oscillations and derived the frequency of maximum power excess, $ν_{\rm max}$, for 20 RGB and 6 EAGB stars. Using asteroseismic scaling relations, we derived mean masses of $\overline{M}_{\rm RGB} = 0.74\pm0.01\,M_{\odot}$ and $\overline{M}_{\rm EAGB}=0.65\pm 0.03\,M_{\odot}$. The inferred integrated mass loss between the two phases is $ΔM_{\rm RGB-EAGB}=0.08\pm 0.03 \,M_{\odot}$. We present an updated mass-loss--metallicity relation for Type I globular clusters, extending it to the very metal-poor regime and supporting decreasing integrated RGB mass loss with decreasing metallicity.

astro-ph.SR↗

arXiv2026

Disco in the Dust: Reflected light at the bow shock around Betelgeuse's companion explains its observed luminosity

Recent detections of $α$ Orionis B, the putative companion to Betelgeuse, have been reported using multiple instruments and techniques. These include, most recently, a $>6σ$ detection using VLT/SPHERE reported by Montarges+2026. The authors infer a bright companion ($\sim10^{-3}\times$ Betelgeuse's luminosity) with a mass of $2-3\,M_\odot$ and $T_\text{eff}\approx10-12{,}000$\,K, loosely consistent with the uppermost bounds of Howell+2025's recent mass estimate from speckle-imaging. However, it is in tension by a factor of two with the reported mass-exclusion limits via non-detection from a recent HST far-UV campaign (Goldberg+2025). While mass identification from isochrone-fitting (conducted in all cases) is prone to uncertainty, the restrictive HST upper limit on FUV flux precludes the hot, blue emission of a $\gtrsim2\,M_\odot$ main-sequence star. This discrepancy is reconciled by the following hypothesis: these detections observe the reflection of Betelgeuse's own luminosity scattered off the companion's bow shock and wake as it traverses the dusty circumstellar medium. To evaluate the feasibility of this scenario, we draw from custom, filter-specific stellar models computed with MESA, as well as Athena++ simulations of the companion's bow shock in idealized conditions. Importantly, the expansive bow shock from a stellar-mass object necessarily subtends a sizable portion of Betelgeuse's outgoing flux. We find that optical luminosity ratios of $\sim10^{-3}-10^{-4}$ are straightforward to resolve within reasonable assumptions about the companion mass and circumstellar dust, and disfavor a hot $3\,M_\odot$ companion. We thereby reconcile competing mass hypotheses across observational campaigns through proper attribution of the observed brightness, motivating future multi-wavelength campaigns to further characterize this enigmatic system.

astro-ph.SR↗

arXiv2026

Asteroseismic Analysis of the Merger Product Red Giant in the $γ$ Persei System

Context. $γ$ Persei is a long-period eclipsing binary system ($P\approx 14.6$ years) containing a red giant primary, and it is well known for its multi-faceted classification as a visual and spectroscopic binary. Its brightness and binary nature together make it a valuable target for both photometric and spectroscopic studies, particularly in the context of asteroseismology and stellar evolution, as the primary star likely formed through a stellar merger. Aims. We aim to determine the seismic parameters $ν_{\rm max}$, $Δν$, and the oscillation amplitudes of the primary component, an evolved giant, to estimate its seismic mass $-$ which we can compare to its estimated dynamic mass. Methods. We use Transiting Exoplanet Survey Satellite (TESS) data obtained during Sectors 58, 85, and 86 and to complement the space-based observations, we incorporate high-resolution RV measurements acquired by the Stellar Observations Network Group (SONG) during two distinct epochs; 2017 and 2024. Results. We successfully detect solar-like oscillations in $γ$ Per and infer a seismic mass of $3.25\pm0.13$ M$_\odot$, which is slightly below the dynamical mass. We find the photometric oscillation amplitudes to be significantly lower than predicted from scaling relations, but in line with other high-mass red giants. We also find that radial velocity amplitudes along the Hertzsprung-Russell diagram cannot be fitted uniformly with current scaling relations.

astro-ph.SR↗

arXiv2026

Long-term optical and near-infrared photometric evolution of SN 2019vxm, an interacting Type IIn supernova

The diversity of Type IIn supernovae is largely driven by the properties of the circumstellar material (CSM) they explode into. We examine the temporal evolution of SN 2019vxm, an interacting supernova that belongs to the class of long-lasting Type IIn events, using multicolor photometry spanning the ultraviolet, optical and near-infrared wavelengths, including over 650 days of optical and 1500 days of IR coverage. The evolution of the spectral energy distribution and bolometric luminosity, as well as the effective temperature and radius of the photosphere, indicates that the supernova was initially surrounded by an optically thick CSM, which was heated and pushed outward by the forward shock of the impacting ejecta. About 80-100 days after the explosion the forward shock and the photosphere decouples, and we observe the receding photosphere of the H-recombination front within the now thinned CSM. Near-IR measurements reveal long-lasting, slowly cooling emission from circumstellar dust around SN 2019vxm and an IR rebrightening about one year after explosion, which we tentatively identify as a signature of an outer CSM region. We find that due to the moving photosphere and the transition from optically thick to partially thin inner CSM, modeling the explosion and subsequent interaction of the ejecta with the CSM to infer progenitor and CSM masses faces difficulties. Nevertheless, the inferred high masses and extremely high mass-loss rates point to a massive progenitor undergoing intense pre-supernova mass loss.

astro-ph.HE↗

arXiv2026

The Isaac Newton Telescope Monitoring Survey of Local Group Dwarf Galaxies-VIII. A Census of Long-Period Variable Stars across the Andromeda Dwarf Satellite System

We present a comprehensive catalog, in the Sloan $i$ and Harris $V$ filters, of long-period variable (LPV) stars in the spheroidal dwarf satellites of the Andromeda galaxy, based on a dedicated survey for variable stars in Local Group dwarf systems. Using photometric time-series data obtained with the Wide Field Camera (WFC) on the 2.5 m Isaac Newton Telescope (INT), we identify approximately 2800 LPV candidates across 17 Andromeda satellites, spanning a broad range in luminosity and variability amplitude. This study is accompanied by a public data release that includes two comprehensive catalogs, a catalog of the complete stellar populations for each galaxy and a separate catalog listing all identified LPV candidates. Both are available through CDS/VizieR and provide a valuable resource for investigating quenching timescales, stellar mass distributions, and the effects of mass-loss and dust production in dwarf galaxies. We derive updated structural parameters, including newly measured half-light radii, and determine distance moduli using the Tip of the Red Giant Branch (TRGB) method with Sobel-filter edge detection, yielding values between $23.38\pm0.06$ and $25.35\pm0.06$ mag.

astro-ph.GA↗

arXiv2025

New theoretical instability regions, period-luminosity relations and masses for blue large-amplitude pulsators

Blue large-amplitude pulsators (BLAPs) are a recently discovered group of hot pulsating stars whose evolutionary status remains uncertain. Their supposed progenitors are either $\simeq 0.3M_{\odot}$ shell H-burning stars or $\simeq 1.0M_{\odot}$ core He-burning stars, both relying on mass loss or a merger event in a (rarely observed) close interacting binary system. With the goal to understand the stellar masses of BLAPs, we therefore carried out a linear non-adiabatic analysis of a grid of models computed using mesa-rsp, with appropriate input stellar parameters $ZXMLT_{\rm eff}$ and convection parameter sets. We discuss the impact of stellar mass, metallicity, helium abundance and convection parameters on the theoretical instability regions of BLAPs. We also derive new theoretical period relations; our theoretical period relations using low stellar masses seem to be in better agreement with the observed period relations. Although only two BLAPS have been observed to be multi-periodic oscillator so far, we analyse theoretical $P_{1O}/P_F$ ratios and compare these values with other classical pulsators. Furthermore, we provide the first asteroseismic mass estimate for the triple-mode pulsator, OGLE-BLAP-030 which seems to be well-constrained in the range of $0.62-0.64 M_{\odot}$ with a high metallicity of $Z=0.07$, albeit with a few sources of uncertainty involved. This would place the BLAP star intermediate to the two proposed mass scenarios so far.

astro-ph.SR↗

arXiv2025

Benchmarking differential reddening in front of globular clusters

Interstellar extinction is a major obstacle in determining accurate stellar parameters from photometry near the Galactic disk. It is especially true for globular clusters at low galactic latitudes, which suffer from significant amounts of, and spatially variable reddening. Although differential reddening maps are available for tens of clusters, establishing and validating the absolute zero point of relative maps is a challenge. In this study, we present a new approach to determine and evaluate absolute reddening zero-points for Galactic globular clusters by combining three-dimensional reddening maps with Gaia DR3 RR Lyrae data. As a first case study, we investigate the low-latitude globular cluster M9. We compare the Gaia photometry and color data of the cluster member RR Lyrae stars to field RR Lyrae stars with accurate parallaxes and whose photometric metallicities match that of M9, as well as to theoretical models. We calculate the dereddened Gaia colors for the M9 stars based on three zero points. We confirm that the original SFD map appears to be overcorrecting the reddening for at least some RR Lyrae stars, albeit not excessively. In contrast, the 3D Bayestar map and the recalibrated version of the SFD map provide physically plausible reddenings, which we accept as lower and upper limits for M9, respectively. Our results provide a physically motivated reddening range for M9, and outline a methodology that can be directly extended to other globular clusters that are accessible to the Gaia mission, and to other multicolor sky surveys, such as the Rubin Observatory.

astro-ph.GA↗

arXiv2025

Rare Find: Discovery and chemo-dynamical properties of two s-process enhanced RR Lyrae stars

We report the serendipitous discovery of two RR Lyrae stars exhibiting significant s-process element enrichment, a rare class previously represented solely by TY Gruis. Our goal is to characterise these objects chemically and dynamically, exploring their origins and evolutionary histories. Using high-resolution spectroscopy from HERMES@AAT and UVES@VLT, we derived detailed chemical abundances of key s-process elements, carbon along with $α$-elements. We also employed Gaia DR3 astrometric data to analyse their kinematics, orbital properties, and classify their Galactic population membership. We compared observational results with theoretical asymptotic giant branch nucleosynthesis models to interpret their enrichment patterns. Both stars exhibit clear signatures of s-process enrichment, with significant overabundances in second-peak elements such as Ba and La compared to first-peak Y and Zr. Comparison with AGB nucleosynthesis models suggests their progenitors experienced pollution of s-process-rich material, consistent with early binary interactions. However, notable discrepancies in dilution factors highlight the need for more refined low-metallicity asymptotic giant branch (AGB) models. We also explore and discuss alternative scenarios, including sub-luminous post-AGB-like evolution or double episodes of mass transfer. Our findings confirm the existence of s-process-enhanced RR Lyrae stars and demonstrate the importance of combining chemical and dynamical diagnostics to unveil their complex evolutionary pathways. Future detailed binary evolution modelling and long-term orbital monitoring are essential to resolve their formation scenarios and assess the role of binarity in the evolution of pulsating variables.

astro-ph.SR↗

arXiv2025

Betelgeuse's Buddy: X-Ray Constraints on the Nature of $α$ Ori B

The $\sim$$2100$d Long Secondary Period of Betelgeuse's optical lightcurve and radial velocity motivated the prediction of a low-mass stellar companion, expected to be at maximal apparent separation from Betelgeuse around December 2024. We carried out Director's Discretionary Time observations with the Chandra X-ray Observatory to identify any X-ray emission from the companion and constrain its nature as either a compact object or young stellar object (YSO). Past X-ray observations occurred at the wrong phase of the companion's orbit for optimal detection prospects and/or lacked the deep exposure required to constrain the typical X-ray luminosities of YSOs. In our 41.85 ks exposure with Chandra, we do not detect an X-ray source at the position of Betelgeuse. For an estimated hydrogen column density $N_H$$=$$6\times10^{22}$ cm$^{-2}$, we place a limit on the X-ray luminosity of $L_X$$\lesssim$$2\times10^{30}$ erg s$^{-1}$ ($\lesssim$$4.7\times10^{-4}L_\odot$) in $0.5$$-$$8$ keV for a 10 MK plasma temperature spectral model, or $L_X$$\lesssim$$5\times10^{29}$ erg s$^{-1}$ ($\lesssim$$1.2\times10^{-4}L_\odot$) for an absorbed power law with photon index $Γ$$=$$2$. These limits robustly exclude an accreting compact object (white dwarf or neutron star) as the companion. Solar mass YSOs with an age similar to Betelgeuse ($\sim$10 Myr) display a range of X-ray luminosities ($10^{28-32}$ erg s$^{-1}$), and we can place upper bounds within this range for most absorbing columns. Based on these considerations, we conclude that the companion to Betelgeuse is likely a low-mass YSO.

astro-ph.SR↗

arXiv2025

Betelgeuse, Betelgeuse, Betelgeuse, Betel-buddy? Constraints on the dynamical companion to $α$ Orionis from HST

Recently, two independent analyses have asserted that the cause of the Long Secondary Period (LSP) observed in the variability spectrum of our nearest red supergiant, Betelgeuse ($α$ Ori), is an as-yet undetected, low-mass binary companion dubbed $α$ Ori B. In this paper, we present the results of a far-UV observational campaign using the STIS echelle spectrograph on the Hubble Space Telescope aimed at detecting spectral signatures of the companion. The four-quadrant tiling pattern and timing of the observations were optimized to isolate the companion, with observations taking place during a period of maximum angular and velocity separation between Betelgeuse and the putative companion. Spectral differencing between quadrants recovers no spectral features at the companion's velocity in excess of the background or Betelgeuse's chromosphere, i.e. a non-detection. Having determined that $α$ Ori B is most likely a Young Stellar Object (YSO) thanks to constraints from a complementary X-ray campaign with the Chandra X-ray Observatory in a companion paper, comparison of our data against canonical spectra from YSOs in the ULLYSES database allows us to confidently exclude masses above $\gtrsim1.5M_\odot$ and companion continuum or line emission in excess of $\approx10^{-14}$ erg s$^{-1}$ cm$^{-2}$ angstrom$^{-1}$ in the FUV ($\approx1200-1700$ angstroms). Future observational campaigns aware of the LSP phase are needed to place deeper constraints on the spectroscopic nature of $α$ Ori B.

astro-ph.SR↗

arXiv2025

Matching seismic masses for RR Lyrae-type and oscillating red horizontal-branch stars in M4

Globular clusters offer a powerful way to test the properties of stellar populations and the late stages of low-mass stellar evolution. In this paper we study oscillating giant stars and overtone RR Lyrae-type pulsators in the nearest globular cluster, M4, with the help of high-precision, continuous light curves collected by the Kepler space telescope in the K2 mission. We determine the frequency composition of five RRc stars and model their physical parameters from linear pulsation models. We are able, for the first time, to compare seismic masses of RR Lyrae stars directly to the masses of the very similar red horizontal branch stars in the same stellar population, independently determined from asteroseismic scaling relations. We find average seismic masses of $0.648\pm0.028\,M_\odot$ for RR Lyrae stars and $0.657\pm0.034\,M_\odot$ for red horizontal-branch stars. While the accuracy of our RR Lyrae masses still relies on the accuracy of evolutionary mass differences of neighboring horizontal branch subgroups, this result strongly indicates that RRc stars may indeed exhibit high-degree, $\ell = 8$ and 9 non-radial modes, and modeling these modes can provide realistic mass estimates. We compare the seismic masses of our red horizontal branch and RR Lyrae stars to evolutionary models and to theoretical mass relations and highlight the limitations of these relations.

astro-ph.SR↗

arXiv2025

Empirical Globular Cluster Ridgeline Construction on Gaia Data

We present a new method and a corresponding code to compress the color magnitude diagram of a globular cluster into a representative curve, called a ridgeline, that can be more readily compared to isochrone models, among other applications. This compression method preserves the physical properties of the cluster, including the morphology of the CMD.

astro-ph.GA↗

arXiv2025

Three fast-spinning medium-sized Hilda asteroids uncovered by TESS

Hilda asteroids, which orbit in a 3:2 resonance with Jupiter, serve as key indicators of dynamical processes in the early solar system. Their spin rates, an important probe of these mechanisms, can constrain their density and collisional evolution, offering valuable insights into their origin. In this paper, we report on the identification of three fast-rotating Hilda asteroids with spin periods in the 3.2--3.7 h range using data from the Transiting Exoplanet Survey Satellite. These rotation periods are significantly shorter than the previous $\sim$5.0 h shortest rotation periods obtained from ground-based observations in the $\sim$10 km size range, and are comparable with the $\sim$3.0 h breakup limit of Hildas a few km in size, derived from the FOSSIL survey. These fast-rotating asteroids require either considerable cohesion (in the order of a few kPa), or densities $ρ$ $\gtrsim$1.5 $gm^{-3}$, in contrast to the typically assumed $ρ$ $\lesssim$1 $gm^{-3}$, to prevent rotational break-up. C-type asteroids, which are common in the outer main belt, have densities of $ρ$ $\approx$1.5 $gm^{-3}$ and are known to comprise a small but notable fraction of Hildas. The observed occurrence rate of the $\leq$4 h rotation periods may be explained by the 10-15% fraction of C-type asteroids, likely mixed into these populations from the outer main belt during giant planet dynamical interactions in the early solar system.

astro-ph.EP↗

arXiv2025

Asteroseismic mass and radius of the naked-eye red giant HD145250

We present the first asteroseismic analysis of the bright, nearby red giant star, HD145250. We calculate the global seismic quantities of the star from single-sector, 2-minute TESS photometry, and determine its mass and radius to be ~1.4 M$_\odot$ and ~16 R$_\odot$ using asteroseismic scaling relations. Our values agree with published non-seismic mass and radius estimates based on comparisons with stellar evolutionary models.

astro-ph.SR↗

arXiv2025

Search for binary-channel metal-rich RR~Lyrae candidates

The existence of dynamically young and metal-rich RR Lyrae stars challenges conventional notions of these variable stars. One possible scenario for their formation and evolution is via binary channels involving mass transfer. This study presents the detection of nine fundamental-mode RR Lyrae stars residing in the thin disk of the Milky Way with metallicities higher than [Fe/H] > -1.0 dex and showing proper motion anomalies. Our thin disk classification is based on kinematics and supported by $α$-element abundances, where possible. We searched for indications of the light-travel time effect (LTTE) in the available literature sources and the TESS photometric data of the stars but found no signs of periodic variations induced by companions within the expected period range. This could be because of a lack of observations as well as sparse measurements and large gaps in the data. We propose a continued search for signs of binarity and a subsequent long-term follow-up of nine targets that satisfy all of our search criteria. Beyond these targets, we also report the detection of slow phase changes in the Blazhko star ST Pic, which could be compatible with the LTTE.

astro-ph.SR↗

arXiv2025

Filling the gap: the missing eclipses of $γ$ Persei from 2005 and from 2006

$γ$ Persei is a long-period ($P \approx 14.6$ yr) eclipsing binary system. Its period makes it a difficult target to fully understand: so far, only two primary eclipses are known in the literature, from 1990 and from 2019, whereas the 2005 one was missed due to its closeness to the Sun at the time. We aimed to fill in this gap by processing the quasi-continuous photometry collected by the Solar Mass Ejection Imager (SMEI) between 2003 and 2011, which was ideally positioned to observe such a bright targets. In order to do that, we first determined a color-dependent conversion formula from the SMEI measurements into {\it Gaia} \textit{G} magnitudes. We applied various corrections to the photometry and provide the longest continuous light curve of $γ$ Persei. We successfully detected the 2005 primary eclipse of the system, with the yearly observations ending during the egress of the companion. We predicted the position of a possible secondary eclipse by forward modeling the binary system with PHOEBE, and successfully recovered the secondary eclipse in the 2006 SMEI observations. The existence of the secondary eclipse puts strong constraints on the orbital configuration, which will be an important constraint for future studies of the system.

astro-ph.SR↗

arXiv2025

Three fast-rotating Jovian Trojans identified by TESS set new population density limits

Here we report on the identification of the three fastest rotating Jovian Trojans with reliable population assignment, using light curve data from the Transiting Exoplanet Satellite Survey mission, also confirmed by Zwicky Transient Facility data. For two of our targets the rotation periods are moderately below the previously accepted ~5 h Jovian Trojan breakup limit (4.26 and 4.75 h), however, the rotation period of (13383) was found to be P = 2.926 h, leading to a density estimate of $ρ$ $\approx$ 1.6 $g cm^{-3}$, higher than the generally accepted $\leq$ 1 $g cm^{-3}$ density limit of Jovian Trojans. If associated with lower densities, this rotation rate requires considerable cohesion in the order of a few kPa. The relatively high albedo (pV $\approx$ 0.11) and fast rotation suggest that (13383) may have undergone an energetic collision that spun up the body and exposed bright material to the surface.

astro-ph.EP↗

arXiv2025

A theoretical framework for BL Her stars IV. New period-luminosity relations in the Rubin-LSST filters

We present new theoretical light curves in the Rubin-LSST filters for a fine grid of BL Her models computed using MESA-RSP. We also derive new theoretical period-luminosity (PL) and period-Wesenheit (PW) relations in the Rubin-LSST filters with the goal to study the effect of convection parameters and metallicity on these relations. The grid of BL Her models was computed with the input stellar parameters: metallicity ($-2.0\; \mathrm{dex} \leq \mathrm{[Fe/H]} \leq 0.0\; \mathrm{dex}$), stellar mass ($0.5M_{\odot}-0.8M_{\odot}$), stellar luminosity ($50L_{\odot}-300L_{\odot}$), and effective temperature (across the full extent of the instability strip; in steps of 50K) and using four sets of convection parameters. Bolometric correction tables from MIST were used to transform the theoretical bolometric light curves of the BL Her models into the Rubin-LSST ugrizy filters. The PL relations of the BL Her models exhibit steeper slopes but smaller dispersion with increasing wavelengths in the Rubin-LSST filters. The PL and PW slopes for the complete set of BL Her models computed with radiative cooling (sets B and D) are statistically similar across the grizy filters. The BL Her models exhibit weak or negligible effect of metallicity on the PL relations for wavelengths longer than the g filter for both the cases of the complete set of models as well as the low-mass models. However, we find significant effect of metallicity on the PL relation in the u filter. Strong metallicity effects are observed in the PWZ relations involving the u filter and are found to have significant contribution from the high-metallicity BL Her models. Due to negligible metallicity effect for relations involving the Wesenheit indices $W(i,g-i)$, $W(z,i-z)$ and $W(y,g-y)$, we recommend these filter combinations for BL Her stars when observed with the Rubin-LSST to be used as reliable standard candles.

astro-ph.SR↗