Solar and Stellar Astrophysics · Cross-listed from physics.class-ph
Short-term solar eclipse predictions using Euclidean geometry and dynamical systems
Alin-Doru Aluas, Valerian-Alin Fodor and Virgilius-Aurelian Minuta
We propose a computationally inexpensive
algorithm to determine whether an opaque spherical body eclipses a luminous one, using only classical geometrical tools. We apply this method to the Sun-Earth-Moon system and predict solar eclipses, including their type, beginning, and duration, using the three-body problem. For predictions over a one-year period, the resulting errors are in the order of minutes.
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Solar and Stellar Astrophysics · Cross-listed from hep-ph
New bounds on light scalars from the tip of the red giant branch
Natnael Debru, Audrey Fung, Saniya Heeba et al. (+3 more)
Light, weakly coupled particles can be copiously produced in the hot and dense interior of
stars, and the resulting energy loss can leave observable imprints on entire stellar populations. For instance, additional energy loss from red giant cores delays helium ignition and brightens the tip of the red giant branch (TRGB). We revisit the TRGB bounds on light scalars coupled to electrons, of which the
Higgs portal is the prototypical example. In the degenerate cores of red giants, scalar emission is dominated by resonant conversion of longitudinal plasmons, which we compute using finite-temperature field theory. Rather than rescaling
neutrino emission rates at fixed
benchmark core conditions, we implement this emissivity in the MESA stellar
evolution code and self-consistently simulate the
evolution of red giants, including the backreaction of the scalar energy loss on the stellar structure. Comparing our predictions with the observed bolometric TRGB magnitudes of 27 Milky Way globular clusters, we exclude scalar-electron couplings $\alpha_{\phi ee} = g_e^2/4\pi > 1.6 \times 10^{-34}$ at 95% confidence for sub-keV masses, improving on previous bounds by nearly two orders of magnitude. In the context of the
Higgs portal, this corresponds to an exclusion on values of the mixing angle $\sin\theta > 2.2\times 10^{-11}$, providing the tightest bound for scalar masses in the $\sim 1\,\mathrm{eV} - 10\,\mathrm{keV}$ range.
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All authors Natnael Debru, Audrey Fung, Saniya Heeba, Hugo Schérer, Katelin Schutz, Aaron C. Vincent
Solar and Stellar Astrophysics · Cross-listed from physics.plasm-ph
Proton Heating Rates in the Inner Heliosphere: Helios Observations
Alaa Fayad, Anna Tenerani and Chadi Salem
Solar wind
protons exhibit a temperature anisotropy that deviates from the double-adiabatic prediction, suggesting an additional energy source. To investigate solar wind heating mechanisms, we analyze Helios 1 and 2 data and characterize the radial
evolution of the adiabatic invariants and anisotropic heating rates of fast wind
protons, considering both the bulk population and its core and beam components separately. Unlike previous studies, we account for
proton heat fluxes and deviations from the Parker spiral caused by large-amplitude fluctuations, which causes significant differences in the parallel heating rates compared to earlier results. Although earlier work has questioned the reliability of power laws to estimate heating rates and proposed as a more robust approach the investigation of the radial
evolution of adiabatic invariants, we show that the two approaches yield consistent results when applied to the same
dataset. Our analysis shows that all
proton populations considered require net perpendicular heating, consistent with earlier studies. In contrast, the parallel energy
evolution differs between populations. Core
protons require parallel heating, whereas beam
protons undergo parallel cooling although the total
proton population undergoes a net parallel cooling. This behavior is consistent with the combined action of
turbulence and core-beam kinetic instabilities, which together can drive preferential perpendicular heating while simultaneously produce parallel cooling in the fast solar wind. Core
proton parallel heating could instead be a signature of Alfvén wave decay.
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Solar and Stellar Astrophysics
Chromospheric sensitivity of stellar spectral lines: an unsupervised machine learning classification
Juan I. Peralta and Mariela C. Vieytes
Stellar
magnetic activity alters thousands of spectral lines, limiting high-precision radial-velocity measurements, abundance analyses, and planetary characterization. We present a preliminary classification of 6403 atomic lines in synthetic visible spectra from a sequence of NLTE semi-empirical dG2 atmospheric models with increasing chromospheric heating. Principal-component analysis shows that the dominant component traces overall response amplitude, while the second distinguishes early from late responders. DBSCAN applied in the full nine-dimensional response space identifies a dense stable core and an activity- sensitive non-core group comprising about 11% of the lines. The stable core provides candidate lines for activity-insensitive measurements, while sensitive lines provide candidate activity diagnostics. Sensitive transitions tend to have low lower-level energies, although the populations overlap, making lower-level energy a statistical discriminator rather than a line-by-line predictor. A spectral sensitivity map shows that small average variations can hide nonlinear or compensating responses, demonstrating the value of the complete line-response trajectory for classification.
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Solar and Stellar Astrophysics
An Open Cluster Origin for Most Solar-Type Binaries in the Solar Neighborhood and Implications for Primordial Planet Stability
Anna C. Childs and Aaron M. Geller
We present the first Gaia-calibrated estimate of the contribution of dynamically processed open clusters (OCs) to the nearby solar-type field binary population and investigate the implications for primordial
planet stability. We combine Gaia DR3 observations, empirical models of cluster formation and dissolution, and direct N-body simulations to constrain the fraction of field FGK-type binaries within 1 kpc that originated in OCs over the past 5 Gyr. We find that at least ~53% of solar-type field binaries formed in OCs with initial masses > 200 M_Sun, where dynamical processing becomes significant. We quantify the effects of stellar encounters and binary orbital
evolution on the stability of both circumbinary and circumstellar
planets by deriving empirical prescriptions for circumbinary
planet destabilization as a function of binary separation and for the fractional reduction of stable circumstellar coplanar phase space. These results provide a framework for evaluating how OC dynamical
evolution may influence the stability of
planets in binary systems and therefore contribute to observed
exoplanet demographics.
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Solar and Stellar Astrophysics
Inflated Supermassive Stars as Little Red Dots and Progenitors of Supermassive Black Holes
Wenbin Lu
JWST has uncovered an abundant population of compact, red sources at high
redshifts, termed little red dots (LRDs). We study whether they could be explained by thermally relaxed, hydrogen-burning, metal-enriched supermassive
stars (SMSs). We construct 1D models in hydrostatic and thermal
equilibrium, including a radiation-pressure-dominated, CNO-burning core and an outer envelope with
metallicity-dependent opacity, non-adiabatic convection, and an effective treatment of super-Eddington surface layers. The luminosity is close to the Thomson-scattering Eddington limit. The Fe-opacity bump drives the formation of a strongly inflated, low-mass envelope, while hydrogen recombination terminates the envelope at a bound photosphere. For M=$10^4$ to $10^6$ Msun and metal mass fractions $Z=10^{-4}$ to $10^{-2}$, we find that the most metal-rich models (Z ~ $10^{-2}$) develop highly inflated envelopes and reach Teff ~ 7000 K. We suggest that such enriched SMSs could instead be assembled through runaway stellar collisions in compact
star clusters. The GR instability sets a maximum mass that depends on the core rotation rate. The nonrotating and rotating models have maximum masses $3\times10^5$ to $3\times 10^6$ Msun, and maximum luminosity of the order $10^{44}$ erg/s, comparable to the observed bright-end cutoff of the LRD luminosity function. Core hydrogen depletion can drive initially stable SMSs across the instability threshold after a lifetime of order 1 Myr. If each LRD leaves a black hole retaining most of its mass, the observed LRD abundance implies a present-day remnant density of order $10^{-2}\rm cMpc^{-3}$, consistent with the local abundance of supermassive black holes. Cool SMSs naturally produce weak X-ray and weak high-ionization lines. Non-LTE effects may significantly modify the Balmer features and the continuum opacity, and may lower Teff below our LTE value.
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Solar and Stellar Astrophysics
The Last Gasps of a Dying Star: ALMA Observations of the Pre-Planetary Nebula IRAS 06530-0213
Raghvendra Sahai, Wouter Vlemmings, Guillermo Quintana-Lacaci et al. (+16 more)
We present high angular-resolution ($\sim 0.{''}1 - 0.{''}5$) ALMA observations of millimeter-wave line and continuum emission (at $\sim0.44$ and $0.88$ mm) in the pre-planetary nebula IRAS 06530–0213 (IRAS 06530). These data show the presence of an extended circular ring – first evidence of the last thermal-pulse preceding the post-AGB phase in a carbon
star – and a central bipolar nebula (CBN) and
torus. The mass-loss rate of IRAS 06530's AGB progenitor decreased immediately after the thermal pulse, then rose again just before the post-AGB phase as evidenced by the presence of filamentary arc structures around the CBN. The arc stuctures are likely part of a 3-D Archimidean spiral structure generally attributed to the presence of a binary companion. But we do not find a compact continuum source at the location of IRAS 06530's central
star, such as that associated with the compact dusty disks typically found in disk-prominent post-AGB objects known to have binary companions. The expansion ages derived for the
torus and CBN imply that IRAS 06530's progenitor transitioned to a post-AGB
star $\lesssim700$ yr ago. The molecular mass of the ejecta in IRAS 06530 is dominated by the filamentary arc region with a mass $M_{H_2}=(0.12-0.25) M_{\odot}$. Compared with solar values, the
torus of IRAS 06530 appears to be significantly (modestly) enriched in $^{13}$C and $^{17}$O ($^{15}$N) as well – a pattern of rare-isotope enrichment inconsistent with standard nucleosynthesis models. From the luminosity of IRAS 06530 and the age of its detached shell, while it was still on the AGB, we infer that the mass of IRAS 06530's progenitor was $(1.6-3.4) M_{\odot}$.
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All authors Raghvendra Sahai, Wouter Vlemmings, Guillermo Quintana-Lacaci, Hyosun Kim, Javier Alcolea, Bruce Balick, Eric G. Blackman, Arancha Castro-Carrizo, Orsola de Marco, Joel H. Kastner, Eric Lagadec, Chin-Fei Lee, Miguel Santander-García, Carmen Sánchez Contreras, Toshiya Ueta, Albert A. Zijlstra, Valentin Bujarrabal, Laurence Sabin, Daniel Tafoya
Solar and Stellar Astrophysics
The "Other" Centuries-Long Record of Solar Magnetic Activity Cycles: Lessons From the Stars
Jason T. Wright, Travis S. Metcalfe, Kristof Petrovay et al. (+1 more)
Studies of space
climate and solar
magnetic activity and studies of stellar dynamos and
magnetic cycles are separated by discipline and by the quality of the data we have to work with: the Sun gives us detailed knowledge of a single
star, while the
stars give us comparatively sparse data across a range of (sometimes poorly known) masses and ages. This review, a collaboration among scientists with expertise in stellar astronomy, space
climate, and solar physics, seeks to provide a guide to what the Sun's and
stars'
magnetic activity records can tell us about how stellar dynamos operate on decadal, millennial, and stellar-evolutionary timescales. It reviews the historical Solar sunspot record, terrestrial cosmogenic isotope records, and decades-long chromospheric activity measurements of dozens of sun-like
stars across a range of masses, ages, and
metallicities near the solar value. Particular emphasis is placed on the Maunder minimum, and the hunt for similar events in the stellar record, especially the recently discovered grand minimum event ongoing in the
star HD 166620. These records show that solar-like dynamos are a common feature of Sun-like
stars, and
magnetic grand minimum events akin to the Maunder minimum might be very rare, with only one identified in 3,000
star-years of
magnetic activity records. Together, solar and stellar dynamo studies are bringing a still-fuzzy picture into focus in which stellar
magnetic activity weakens as
stars spin down over billions of years towards a critical Rossby number near the solar value, at which point stellar cycles begin to be frustrated. These periods of frustration manifest as
magnetic grand minima, and increase in frequency until they become permanent and
stars enter a period of very low and constant
magnetic activity.
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All authors Jason T. Wright, Travis S. Metcalfe, Kristof Petrovay, Hisashi Hayakawa
Solar and Stellar Astrophysics
Super-Chandrasekhar white dwarfs by the evolution of magnetized main-sequence stars: New mass-limits from STARS simulation
Zenia Zuraiq, Banibrata Mukhopadhyay, Achal Kumar et al. (+4 more)
We explore the time
evolution of the magnetized main-sequence
stars (MSs) to magnetized non-rotating white dwarfs (WDs) with a series of models, capturing modified Hertzsprung-Russell diagram. We use the Cambridge Stellar
evolution code,
STARS, with modifications by introducing
magnetic effects and cooling. We investigate the possible existence of stable, magnetized, massive, super-Chandrasekhar, approximately spherical WDs, away from Chandrasekhar's mass-radius curve. These we refer to as B-WDs. They are inferred from the observations of peculiar over-luminous type Ia
supernovae, e.g. SN2003fg. We show that the classical effects of
magnetic fields significantly impact MSs and their time
evolution to WDs. Moreover, the
magnetic field could be decisive in explaining the unusually large radius observed in some sub-Chandrasekhar WDs, e.g. SDSS J123204.19+522548.2, along with the finite temperature effect. We further investigate the stability of magnetized WDs, both below and above the Chandrasekhar limit and confirm the possibility of super-Chandrasekhar B-WDs with new mass limits that depend on the
magnetic field geometry, mass
accretion from a companion and cooling rates. Therefore, while the "Chandrasekhar limit" may be sacrosanct, its value severely depends on the underlying physics, here the
magnetic field.
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All authors Zenia Zuraiq, Banibrata Mukhopadhyay, Achal Kumar, Arnab Sarkar, Alexander J. Hackett, Projjwal Banerjee, Christopher A. Tout
Solar and Stellar Astrophysics
A Quantitative Method to Investigate the Spectral Class Time Evolution of Novae
Maria Kopsacheili, Martín Guerrero and Diego Alejandro Vasquez Torres
Novae are spectroscopically classified as Fe II or He/N according to the dominance of Fe II, or He and N emission lines in their pre-nebular spectra, while spectra exhibiting both are classified as hybrid. Evidence suggests that these spectral classes represent spectral
evolution. We investigate this scenario using a large spectroscopic
dataset and introduce a quantitative coefficient, $\kappa$, to characterise the relative strength of Fe II and He/N emission. The coefficient is defined as the ratio of the flux of the Fe II ($\lambda5169$) line to the mean flux of five He and N emission lines, with $\kappa>1$ indicating Fe II-dominated spectra and $\kappa<1$ indicating He/N-dominated spectra. We apply this method to 26 novae using spectra from the Astronomical Ring for Amateur Spectroscopy (ARAS) Database and compare the
evolution of $\kappa$ with optical light curves. Fifteen of the 24 classical novae and one of the two recurrent novae exhibit at least one transition between Fe II- and He/N-dominated phases, while temporal trends suggest this fraction could approach 90% with complete spectroscopic coverage. The $\kappa$ coefficient closely tracks the optical light curves and repeatedly crosses unity in novae exhibiting jitters, revealing non-monotonic spectral
evolution linked to brightness fluctuations. These results support the interpretation of Fe II, He/N, and hybrid spectra as evolutionary stages rather than distinct nova types and establish $\kappa$ as a quantitative tool for tracing nova spectral
evolution while reducing biases from incomplete spectroscopic coverage.
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Solar and Stellar Astrophysics
Multi-Epoch Stability in the Rotational Modulation of the Planetary-Mass Companion Ross 458C
Elena Manjavacas, Jared Bull, Paulo Miles-Paez et al. (+7 more)
Spectroscopic variability is detected in brown dwarfs across all spectral types, suggesting atmospheric patchiness in brown dwarf atmospheres. We present JWST/NIRSpec time series observations of the T8.0 planetary-mass companion Ross 458C. We compared our derived spectral variability and light curve to those obtained using HST/WFC3 observations more than 7.5 yr before and published by Manjavacas et al. (2019). We found that the light curve of Ross 458C is remarkably similar in the two epochs in terms of shape and variability amplitude potentially created by stable weather patterns. We measured a rotational period of 11.57+\-0.09 hr, demonstrating that the previously reported HST/WFC3 period of 6.75+\-1.58 hr is most likely a second-order harmonic produced by an unresolved double-peaked rotational modulation, likely due to the higher uncertainties of the HST/WFC3 light curve and the short time baseline of those observations. We measured the variability amplitude in the white light curve created using only the wavelength range covered by HST/WFC3 (1.10-1.63 micron), obtaining a value of 1.47+\-0.18%, which is consistent with that measured in the HST/WFC3 light curve.
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All authors Elena Manjavacas, Jared Bull, Paulo Miles-Paez, Natalia Oliveros-Gomez, Theodora Karalidi, Ben W. P. Lew, Zhoujian Zhang, Yifan Zhou, Daniel Apai, Xianyu Tan
Solar and Stellar Astrophysics · Cross-listed from astro-ph.EP
Asteroids Impacting the Solar System Planets and the Moon. II: Comparison with Observational Impact Records
Qifeng Cheng and Daniel Scolnic
Planetary impact rates are difficult to infer from observations alone because impacts are rare, observational records are target-dependent, and converting observed flashes, bolides, and craters to an intrinsic impact rate depends on uncertain selection effects and conversion parameters. Building on the simulations in Paper I, we examine whether observational systematics can explain the order-of-magnitude mismatch between observed and modeled impact rates on Earth, and whether comparable discrepancies extend to other Solar System bodies. We convert 12 observed impact records for Earth, the Moon, Mars, and Jupiter to a common pre-atmospheric impact rate for $D>10$ m, propagate uncertainties through the conversion chain, and compare the resulting rates with the intrinsic rates derived in Paper I. We find discrepancies for Earth (observation-to-model median ratio $2.2-21.0$), the Moon ($3.4-132.1$), Mars ($14.2-118.6$), and Jupiter ($2.6-47.7$), with the dominant source of the discrepancy differing by body. The simulated Jupiter-family comet (JFC) contribution substantially reduces the Earth discrepancy, suggesting that an additional dynamical source may help explain the gap. The lunar records disagree with each other by two orders of magnitude, with the discrepancy dominated by size-extrapolation uncertainties. The Mars mismatch is dominated by crater-to-impactor conversion. The Jupiter comparison depends mainly on uncertainties in the inferred number of bound impactors and in the observational completeness thresholds. Further investigation of this mismatch requires incorporating cometary modeling and tighter constraints on size-extrapolation scaling and improved observational completeness.
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Solar and Stellar Astrophysics
Searching for Massive Remnant Planetary System Hosts with White Dwarf Gaia XP Spectra
Lou Baya Ould Rouis, J.J. Hermes, Pierre Bergeron et al. (+5 more)
Remnant planetary systems around massive white dwarfs ($M_{\rm WD} > 0.8\,{\rm M}_\odot$) are intrinsically rare and remain poorly characterized. As the evolutionary endpoints of intermediate-mass B- and A-type
stars, these white dwarfs provide valuable constraints on the formation and survival of planetary systems around higher-mass progenitors. In the absence of large, dedicated spectroscopic surveys, extremely-low-resolution Gaia XP spectra provide a powerful means of identifying candidate metal-polluted white dwarfs. We obtained follow-up observations with low-resolution optical spectroscopy (R=500-4000) to search primarily for Ca II H & K absorption in massive, metal-polluted white dwarf candidates selected from Gaia XP spectra to increase the sample of massive remnant planetary system hosts among objects with effective temperatures below $\sim15{,}000$ K. We find that Gaia XP spectra recover metal-polluted white dwarfs efficiently, confirming 82$\pm$5% recovery of photospheric metals (59 of 72 targets) in high-confidence candidates of our sample (with classifier probability $P_{\rm DZ} > 0.65$). However, Gaia photometric masses derived from $G$, $G_{BP}$, and $G_{RP}$ broad-band photometry are not sufficient to identify the most massive systems, as reliable mass determinations require detailed metal-enriched atmospheric fits. We present a selection of cool white dwarfs confirmed to be both massive and metal polluted, demonstrating that Gaia XP spectra can substantially expand the sample of white dwarf
exoplanet hosts. Our search led to the discovery of a new transiting debris system, SDSS J1624+5404, the 21st published system to date and eighth to show periodic transits.
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All authors Lou Baya Ould Rouis, J.J. Hermes, Pierre Bergeron, Simon Blouin, Stefan Arseneau, Tim Cunningham, Joseph A. Guidry, Ciarra Coston
Solar and Stellar Astrophysics · Cross-listed from astro-ph.IM
The optical high-resolution spectral archive of the HERMES spectrograph mounted on the 1.2m Mercator telescope
Hans Van Winckel, Saskia Prins, Gert Raskin et al. (+13 more)
Context. The HERMES spectrograph is a high-resolution, fibre-fed optical spectrograph of the 1.2m Mercator
telescope operated from the Roque de los Muchachos observatory in Spain. HERMES started its scientific operations in June 2009 and has been the workhorse instrument since then. Regular instrument updates have been crucial. They have helped to ensure the continued provision of high-quality spectra. This will continue both now and in the future. Aims. With this contribution we review over 16 years of HERMES operations and we launch and introduce the archive to the interna- tional community at large. We describe the overall performances of the HERMES spectrograph and list the most important instrument upgrades since the start of the operations. We release about 150 000 high-resolution spectra to the community and describe global properties of the datarelease. We use a standard propriety period of 1 year with some exceptions. Methods. We used the German Astrophysical Virtual Observatory (GAVO) DaCHS platform to present the archive in a Virtual Ob- servatory (VO) compatible form with both an access via a dedicated webinterface, and via VO-compliant tools like PyVO, TOPCAT, Aladin etc. We illustrate the use in several worked-out examples to search and download the fully wavelength-calibrated,
cosmic- cleaned and barycentric corrected 1D spectra. Results. With this contribution we provide the needed information of the data product and offer a reference paper for the users of the HERMES archive.
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All authors Hans Van Winckel, Saskia Prins, Gert Raskin, Jesus Perez Padilla, Wim Pessemier, Wim De Meester, Maarten Dirickx, Yves Frémat, Alain Jorissen, Holger Lehmann, Kwinten Missiaen, Maddalena Reggiani, Hugues Sana, Andrew Tkachenko, Bart Vandenbussche, Christoffel Waelkens
Solar and Stellar Astrophysics · Cross-listed from astro-ph.EP
Rotational Mapping and Regional Atmospheric Retrievals of Variable Brown Dwarfs: Application to Luhman 16B and SIMP 0136
Ruizhe Wang, Heather A. Knuton, Julie Inglis et al. (+1 more)
We present a
Bayesian framework for converting time-resolved spectroscopy into rotation-inferred regional spectra and atmospheric constraints for variable brown dwarfs. We derive an analytic mapping framework with evidence-optimized regularization and uncertainty propagation by marginalizing over physical parameters and model complexities. We provide methods for selecting characteristic spectral end-members from the inferred surface maps, and highlight the advantage of analyzing these rotation-inferred regional spectra over the disk-integrated time-resolved observations, while explicitly accounting for the
geometric degeneracies inherent to rotational mapping. We apply this framework to published JWST/NIRSpec rotational monitoring of Luhman 16B and SIMP 0136. For both objects, we identify dominant spectral regions and retrieve regional variations in cloud structure, thermal gradients, and chemistry that are consistent with cloud radiative feedback. In addition, we demonstrate the importance of limb darkening in deriving surface maps. These results establish a statistically controlled method for linking rotational spectral variability to atmospheric heterogeneity and enable future rotational mapping and regional atmospheric studies of giant
planet atmospheres.
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All authors Ruizhe Wang, Heather A. Knuton, Julie Inglis, Xianyu Tan
Solar and Stellar Astrophysics · Cross-listed from astro-ph.GA
Stellar Yields of Rapidly Rotating Population III Stars for the High Redshift Universe
Devesh Nandal, Konstantinos Topalakis, Vasilisa Sergienko et al. (+6 more)
JWST has revealed rapid nitrogen enrichment in high
redshift galaxies, renewing the need for stellar yields that follow metal free
stars beyond the main sequence and across their final fates. We present Geneva stellar
evolution models of rapidly rotating Pop~III
stars with $5 \leq M_{\rm ini}/M_\odot \leq 200$ and $\upsilon_{\rm ini}/\upsilon_{\rm crit}=0.7$, evolved to the end of core O-burning. We calculate gross adopted ejecta masses using fate dependent remnant prescriptions spanning core collapse, pulsational pair instability, and complete pair instability. Our quantitative results focus on hydrostatically produced CNO material, while heavier species are treated as final-model reservoirs. Rotation produces primary CNO material by mixing newly synthesized C and O into H-burning layers, where CNO cycling generates nitrogen. The resulting abundance signature depends strongly on which stellar layers escape. Models leaving compact remnants can reach $\log({\rm N/O})=-0.49$ while remaining poor in Si/S/Ar/Ca-rich material. PISN models eject the largest nitrogen masses, $M_{\rm N}=1.8$–$2.5,M_\odot$, but also release $57$–$65,M_\odot$ of oxygen, lowering $\log({\rm N/O})$ to $-1.44$ to $-1.29$. Thus, high nitrogen yields do not imply high N/O ratios. This trend persists after IMF weighting, as increasingly top-heavy populations add oxygen and deep alpha material faster than they build a nitrogen dominated mixture. Our grid provides a new CNO-focused
prompt-enrichment
dataset for interpreting nitrogen-rich systems including GN-z11, CEERS-1019, and GS~3073.
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All authors Devesh Nandal, Konstantinos Topalakis, Vasilisa Sergienko, Doga Eker, Efe K. Celep, Danielle A. Berg, Daniel J. Whalen, Sophie Tsiatsiou, Raphael Hirschi
Solar and Stellar Astrophysics · Cross-listed from astro-ph.GA
Stellar ages from [C/N] in giant stars: applicability and limitations
Giada Casali, Luca Casagrande, Fiorenzo Vincenzo et al. (+5 more)
The [C/N] abundance ratio is a powerful age indicator for giant
stars, enabling age estimates for spectroscopic samples where traditional methods are limited. We calibrate a multivariate [C/N]-age-[Fe/H] relationship using 9,122 giant
stars observed by Kepler, with asteroseismic ages and APOGEE DR17 abundances. The calibration is performed separately for lower red giant branch (LRGB), upper RGB (URGB), and red clump (RC)
stars. We validate the relationships using independent samples from K2, TESS, and open clusters, finding good agreement with reference ages, particularly for LRGB
stars, with typical precision of ~30% for ages between ~2 - 10 Gyr. The performance degrades for URGB and RC
stars and low
metallicities, likely due to extra mixing processes, for young (<2 Gyr) and old (>10 Gyr)
stars, where the [C/N]-age correlation weakens. We show that the [C/N]-based ages reproduce known Milky Way features, including the age distribution across the [alpha/Fe]-[Fe/H] plane and the flaring of the Galactic disc. Compared to other chemical clocks, [C/N] provides more robust and precise age estimates within its domain of validity. Our results demonstrate that [C/N], combined with
metallicity, is an effective empirical tool for deriving stellar ages of giant
stars from spectroscopic surveys, particularly for LRGB
stars with [Fe/H] > -1, enabling Galactic archaeology studies beyond the reach of current asteroseismic samples.
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All authors Giada Casali, Luca Casagrande, Fiorenzo Vincenzo, Andrea Miglio, Melissa Ness, Grazina Tautvaišiene, Laura Magrini, Sven Buder
Solar and Stellar Astrophysics · Cross-listed from astro-ph.EP
Time-resolved JWST Retrieval Analysis of the Coldest Brown Dwarf: Temperature and Chemical Variations in WISE 0855-07
Harshil Kothari, Caroline V. Morley, Brittany E. Miles et al. (+12 more)
WISE J0855-07 is the coldest known brown dwarf (estimated Teff~250 K), offering a rare opportunity to probe atmospheric physics in the temperature and mass regime that overlaps directly with
exoplanets. At these temperatures, modest perturbations to the thermal structure and chemical abundances can produce measurable changes in the emergent mid-infrared spectrum, making time-resolved spectroscopy a powerful way to test whether the atmosphere is longitudinally and temporally homogeneous. Using James Webb Space
Telescope NIRSpec/G395M time-series spectra spanning ~3 to 5.2 {\mu}m over 11 hr, we analyze every third spectrum from the
dataset with a series of time-resolved atmospheric
retrievals using the Brewster
retrieval framework. Using this approach, we model epoch-to-epoch changes in the atmospheric state that drive the observed variability, including the thermal structure and key molecular abundances. From the time-series
retrievals, we find that the primary source of the observed spectral variability is driven by the variations in the thermal structure, which range from ~1 to <100 K from epoch to epoch, particularly between the pressures of ~0.4 and 10 bar. In addition, changes in the abundances of CO, and possibly PH3 and CO2, further modulate the spectrum within specific molecular features. These measurements provide a
retrieval-based view of atmospheric variability in an ultracold,
planet-like object, directly constraining how thermal and chemical structure evolve on observable timescales.
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All authors Harshil Kothari, Caroline V. Morley, Brittany E. Miles, Melanie J. Rowland, Natasha Batalha, Michael C. Cushing, Andrew J. Skemer, James Mang, Brianna Lacy, Johanna M. Vos, Channon Visscher, Adam C. Schneider, Genaro Suarez, Mikayla J. Wilson, Allison M. McCarthy
Solar and Stellar Astrophysics
GIARPS simultaneous optical and infrared high-spectral-resolution observations of Cepheids I. Limb darkening from cross-correlated radial velocities
N. Nardetto, R. S. Rathour, M. C. Bailleul et al. (+17 more)
The Baade-Wesselink method, while theoretically applicable for calibrating the distance scale via Cepheids, is not currently employed in the
cosmic distance ladder. There are various versions of this method. In all these approaches, the projection factor used to convert the radial into the pulsation velocity remains the limiting quantity. By comparing for the first time simultaneous cross-correlated optical and H-band radial velocities of five Cepheids, we aim to better understand the
geometric part of the projection factor that is directly linked to the limb darkening of the
stars. The five Cepheids were observed with the HARPS-N and GIANO-B instruments mounted at the Telescopio Nazionale Galileo in the GIARPS configuration. A two-parameter linear fit was applied to the simultaneous radial velocity measurements of each
star in order to extract the amplitude ratio of both curves (fVH) as well as the difference in mean velocities. We find a mean value of fVH of 1.056 with a root mean square over the five
stars of 0.016, which means that the V-band radial velocity amplitudes are around 5% larger than the ones obtained in the H band. In addition, we find that the H-band radial velocity curves have an average (i.e., a gamma-velocity) of about 1 km/s blueshifted compared to the visible ones, except for one
star, X Cyg, which has a blueshift of 0.4 km/s. At first order, the fVH values are directly linked to the ratio of limb darkening coefficients in both bands (or equivalently the ratio of geometrical projection factors). The fVH values are found to be consistent with expectations from static stellar atmosphere models. This work shows that the differential limb darkening of Cepheids in visible and H bands, and consequently the geometrical part of the projection factor, follows what is expected from stellar atmosphere models.
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All authors N. Nardetto, R. S. Rathour, M. C. Bailleul, V. Hocdé, P. Kervella, G. Bras, W. Gieren, J. Storm, G. Pietrzynski, B. Zgirski, P. Wielgorski, A. Merand, A. Gallenne, E. Poretti, M. Rainer, L. Breuval, M. Duparc, B. Apostolova, W. Kiviaho, K. Sivkova
Solar and Stellar Astrophysics
Orbital and stellar parameter determination of eclipsing $\beta$ Cep pulsators
C. I. Eze, G. Handler, F. Kahraman Aliçavuş et al. (+2 more)
Eclipsing binaries provide precise constraints on stellar properties and
evolution, making those hosting $\beta$ Cep pulsators particularly valuable for characterising massive pulsating
stars. In this paper, thirteen eclipsing binaries with massive primary components are spectroscopically and photometrically analysed to derive the orbital and stellar parameters, and infer their possible evolutionary status. The systems were spectroscopically observed using SALT HRS, HERMES, CHIRON and a spectrograph at Skalnate Pleso Observatory (SPO), and photometrically observed using TESS. Radial velocities and atmospheric parameters are determined, binary systems are modelled, and their absolute parameters are derived using appropriate modelling tools. The rotational properties, circularisation, and synchronisation of the systems are also investigated, and the general properties of the sample are discussed. The sample shows one slow rotator, two circularised and synchronised fast rotating systems, as well as five circular and five eccentric systems with asynchronous fast rotation. The systems are predominantly SB1 or SB2 with faint companions, resulting in dynamical mass estimates at $5$ – $12\%$ precision and radius estimates at $1.5$ – $3.9\%$ precision. The secondary components appear to cut across a wide mass spectrum ranging from low-mass to intermediate mass systems. The eccentricity of the systems shows certain trends with the projected rotational velocity ($v \sin i$) although there is no universal correlation between them. Also, there could be circularisation without co-rotation or synchronisation even for circularised short-period close binary systems.
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All authors C. I. Eze, G. Handler, F. Kahraman Aliçavuş, T. Pawar, P. De Cat
Solar and Stellar Astrophysics
SN 2026dix: a nearby, transitional Type IIb/Ib supernova consistent with a warm supergiant progenitor
Tamás Szalai, Schuyler D. Van Dyk, Dominik Bánhidi et al. (+20 more)
Understanding the final
evolution stages of (very) massive
stars and their explosive outcomes, stripped-envelope
supernovae (SESNe), represent a long-term challenge for astrophysics. The latest results support a continuous distribution within the traditional SESN subclasses (IIb, Ib, Ic). The nearby ($D \approx 17.5$ Mpc) SN 2026dix seems to be another member of the recently identified group of transitional Type IIb/Ib explosions. A point source is located at the SN position within the uncertainties on multiple pre-explosion HST images. Together with post-explosion photometry and spectroscopy, it provides a good opportunity to study a rare type of SN in detail. We carried out a thorough comparative light-curve (LC) and spectral analysis of SN 2026dix. We also constructed its bolometric LC and modeled it semi-analytically. In addition, we constructed the spectral energy distribution of the presumed progenitor and compared this to model stellar atmospheres and binary stellar
evolution tracks. We infer that SN 2026dix arose from an explosion in an interacting binary system, consistent with the properties of a warm ($T_\textrm{eff} \approx 6750-$7750 K; spectral type F2 to A7), luminous ($\log(L_{\rm bol}/L_{\odot})\approx 4.9-5.3$) supergiant primary and a less luminous, less massive hot dwarf companion. The nature of the identified progenitor closely resembles that of some other known cases of SNe IIb and also well aligns with both the results of our semi-analytical LC modeling and the comparison of the LCs and spectra of SN 2026dix with the output of radiative-transfer models of an exploding
star with $M_\textrm{ini}$ = 18 $M_{\odot}$.
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All authors Tamás Szalai, Schuyler D. Van Dyk, Dominik Bánhidi, Andrea P. Nagy, Réka Könyves-Tóth, Alexei V. Filippenko, Thomas G. Brink, WeiKang Zheng, Imre Barna Bíró, István Csányi, Zsófia Bora, Zsóka Horváth, Ágoston Horti-Dávid, András. P. Joó, Dávid Koller, Levente Kriskovics, Klára Lelkes, Katalin Nagy, Krisztián Sárneczky, Ádám Sódor, Róbert Szakáts, András Pál, József Vinkó
Solar and Stellar Astrophysics · Cross-listed from astro-ph.EP
JWST MEP - A World Under Spotty Starlight: Detection of CO2 and H2O in the Hot Saturn WASP-52b with JWST NIRSpec G395H
JWST GO 3969 Team: Yanbo Pan, Ryan J. MacDonald, Néstor Espinoza et al. (+20 more)
Exoplanets orbiting active
stars offer distinct challenges for atmospheric characterization with the JWST. Among such worlds, the hot Saturn WASP-52b (Teq $\sim$ 1300 K) orbits an active K-dwarf that complicates transmission spectroscopy via stellar contamination. Here, we present the first JWST NIRSpec G395H (2.8-5.2 $\mu$m) limb-averaged transmission spectrum of WASP-52b obtained through the JWST Morning/Evening Program (GO-3969), which aims to measure limb asymmetries across a sample of hot giant
exoplanets. Our spectrum reveals the first detection of CO2 in WASP-52b's atmosphere (ln B = 54 / >10$\sigma$), with a retrieved abundance of log CO2 = -5.09 (+1.09/-1.14), and confirmation of H2O (ln B = 5.9 / $\sim$3-4$\sigma$), with an abundance of log H2O = -3.41 (+1.04/-1.04). We find a steep near-infrared slope that cannot be explained solely by H2O absorption, necessitating unocculted starspots (ln B = 5.7 / $\sim$3-4$\sigma$), though with properties that vary across our data reductions. The shape and amplitude of the molecular bands additionally suggest high-altitude (<10 mbar) inhomogeneous clouds covering $\approx$40 $\pm$ 20% of the terminator (ln B = 1.9 / $\sim$2.5$\sigma$), which provides evidence for the morning-evening terminator differences that are consensus predictions of general circulation models. WASP-52b's atmospheric
metallicity can be sub-solar, solar, or super-solar, due to order-of-magnitude uncertainties in the molecular abundances caused by degeneracies between compositions, clouds, and starspots. However, chemical
equilibrium retrievals provide a similar statistical fit while favoring a tighter constraint with a super-solar
metallicity (M/H = 14.8 (+12.1/-5.9) $\times$ solar). These results highlight that chemical detections and aerosol properties may still be recovered for
planets orbiting active
stars via transmission spectroscopy.
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All authors JWST GO 3969 Team: Yanbo Pan, Ryan J. MacDonald, Néstor Espinoza, Bibiana Prinoth, Zafar Rustamkulov, Luis Welbanks, Daniel Kitzmann, Nicolas Crouzet, Anna Walde, Diana Powell, Eva-Maria Ahrer, Adam J. Burgasser, Duncan A. Christie, Wolf Cukier, Carlos Gascón, Måns Holmberg, Thomas Kennedy, Mercedes López-Morales, N. J. Mayne, Dominic Samra, Arjun B. Savel, Maria E. Steinrueck, Christopher P. Wirth
Solar and Stellar Astrophysics
Stability Analysis of the Proton Hammerhead Distribution Observed by Parker Solar Probe: Linear Theory and Fully Kinetic Simulations under Idealised Conditions
L. Pezzini, J. L. Verniero, F. Bacchini et al. (+3 more)
The non-adiabatic heating of the slow Solar Wind (SW) remains an open problem, with wave–particle interactions as a primary candidate mechanism. Novel in situ Parker Solar Probe (PSP) observations reveal strongly perpendicular anisotropic velocity distribution functions (VDFs), called "hammerhead", correlated with intense wave activity. These VDFs are systematically measured at the Heliospheric Current Sheet (HCS), making the hammerhead an important kinetic signature of the slow SW. In this work, we employ a fully kinetic particle-in-
cell approach, complemented by a linear Vlasov solver to cross-validate the simulation results, to investigate the stability of these VDFs, the timescales over which they evolve, and their interaction with
plasma waves. Our main findings indicate that the hammerhead distribution is primarily susceptible to drift-type instabilities, while energy is nonlinearly transferred back to the
plasma through a combination of Landau and cyclotron resonances, resulting in net heating in the parallel direction, preferentially energizing the beam
proton population. Crucially, these nonlinear interactions do not drastically alter the morphology of the distribution. This suggests the possibility that the hammerhead may be generated locally within the HCS in the inner heliosphere and subsequently advected outward, where it is eventually measured by PSP. This work lays the ground for future investigations into the kinetic physics of the HCS.
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All authors L. Pezzini, J. L. Verniero, F. Bacchini, A. N. Zhukov, G. Arrò, R. A. Lòpez
Solar and Stellar Astrophysics · Cross-listed from astro-ph.HE
Core-collapse supernovae 2022prr, 2023ucy, and 2024ljc in the luminous infrared galaxy NGC 6745
K. K. Matilainen, E. Kankare, T. Nagao et al. (+19 more)
The core-collapse
supernovae (CCSNe) 2022prr, 2023ucy, and 2024ljc exploded within the central regions of the nearby luminous infrared
galaxy (LIRG) NGC6745. We present our follow-up data with the aim to characterise the spectrophotometric
evolution of these CCSNe, determine their host-
galaxy extinction, and to define their physical nature. The presented spectrophotometric data set covers the optical and near-infrared region for our three
supernovae (SNe). The data are analysed and compared to other hydrogen-rich CCSNe, and a host-
galaxy extinction value Av is derived based on broadband photometry for each of the targets. A spectral energy distribution (SED) for the host
galaxy is constructed, and a combination of different galactic components are fitted to the SED to estimate the intrinsic CCSN rate and the age of the starburst of NGC6745. 2022prr is a SN2009ip-like event, whose light curve
evolution consists of two consecutive luminous events A and B with peak magnitudes of Mr = -14.8 and -18.3 mag, respectively. The high degree of V and R-band polarisation (P=2.8%) near maximum light suggests interaction with highly aspherical circumstellar material. The spectral
evolution of the SN is dominated by narrow Balmer emission lines, which have a complex
evolution over time. 2022prr joins the growing sample of SN2009ip-like events that show early `flash ionisation' features of CIII, NIII, and HeII. 2023ucy is found to be a normal Type IIP SN. However, 2024ljc is a rapidly evolving Type IIb SN with a post-maximum r-band decline of roughly 3.2 mag by +41 d whereas normal IIb SNe decline typically by 1.5+/-0.3 mag during the same timescale. While the events exploded in a LIRG, the SNe are obscured by only moderate V-band host extinctions ranging from 0 to 1 mag. Based on the SED modelling we estimate an age of the host starburst to be 40Myr, and the intrinsic CCSN rate to be 0.4+/-0.1 SN/year.
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All authors K. K. Matilainen, E. Kankare, T. Nagao, T. Reynolds, A. Efstathiou, S. Mattila, C. R. Angus, A. Reguitti, Y.-Z. Cai, M. Fraser, L. Galbany, M. González-Bañuelos, C. P. Gutiérrez, T. Kangas, T. L. Killestein, T. Kravtsov, P. Lundqvist, S. Moran, A. Pastorello, A. Popowicz, I. Salmaso, M. Stritzinger
Solar and Stellar Astrophysics · Cross-listed from astro-ph.HE
COBALT-BLUE: a fast and accurate model for gravitational self-lensing binary systems
Danny J. Dixon, Adam Ingram, Matthew J. Middleton et al. (+5 more)
We present COBALT-BLUE, a fast public model for the optical light curve of a luminous
star in a non-accreting binary with a compact object. The model includes gravitational self-
lensing, Doppler beaming, ellipsoidal variations, eccentric orbital geometry, and wavelength-dependent limb darkening. In sufficiently edge-on systems, it predicts sharp periodic self-
lensing flares together with phase-locked orbital modulation outside the
flare. We improve upon earlier models by including non-linear limb darkening laws based on stellar atmosphere simulations to calculate the self-
lensing flare profile. This enables light curves to be self-consistently calculated in multiple wavebands from one set of physical parameters, thus offering the prospect of constraining binary parameters such as compact object mass from photometry alone if multiple self-
lensing flares are observed. We also include the option to utilise simpler limb darkening prescriptions to save computational expense. As a proof of principle, we fit our model to ZTF data of 14 candidate self-
lensing sources. The model describes the
flare morphology well for most candidates, but we find that the best fitting parameters are not physically plausible. We conclude that the observed
flares are most likely stellar
flares and not self-
lensing events. In future, we plan to use the model to systematically search optical survey data for signatures of binary motion.
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All authors Danny J. Dixon, Adam Ingram, Matthew J. Middleton, Adam McMaster, Grzegorz Wiktorowicz, Hugh Dickinson, Allison Crossland, Eric C. Bellm
Solar and Stellar Astrophysics
The independence of the mid-infrared RR Lyrae Period-Luminosity relation from metallicity from a study of three globular clusters in the Large Magellanic Cloud
Steve Ardern, Vicky Scowcroft and Stijn Wuyts
RR Lyrae are pulsating variable
stars tracing old ($>10$ Gyr) stellar populations, and exhibit a strong mid-infrared Period-Luminosity (PL) relation that can be calibrated with known parallaxes to infer distances. Here we present Period-Luminosity relations and distance moduli for three isolated globular clusters in the Large Magellanic Cloud: Reticulum, NGC 1841, and NGC 1466. Our analysis uses legacy Spitzer Space
Telescope images obtained by the Carnegie RR Lyrae Program, and an internally self-consistent sample restricted to RRab
stars, with cluster membership confirmed using Gaia DR3 proper motions and photometry. In the Spitzer 3.6~$\mu$m band, we simultaneously fit a PL for these clusters using a slope derived from Galactic Globular Clusters, yielding extinction-corrected distance moduli of $18.47\pm0.09$ mag for Reticulum, $18.29\pm0.09$ mag for NGC 1841, and $18.61\pm0.09$ mag for NGC 1466. The latter two are the first RR Lyrae PL-based distance moduli for these clusters, and all three are consistent with literature values from other techniques. Additionally we fit a PL with slope as a free parameter, and find that this LMC-derived PL is consistent with that derived from Galactic GCs. Simultaneously fitting a PLZ for the three clusters yields a
metallicity coefficient $c= -0.03\pm0.05~\mathrm{mag}~\mathrm{dex}^{-1}$ which can be considered a negligible dependence of the PL on
metallicity ($|c| <0.1$ mag dex$^{-1}$). Modelling an intrinsic width, $W$, to the PL/ PLZ yields a consistent value $W\approx0.1\pm0.02~\mathrm{mag}$, suggesting intrinsic width is not driven by
metallicity.
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