We present a substantial update to the MESA Isochrones and Stellar Tracks (MIST) library, extending the MIST model grids and isochrones down the white dwarf (WD) cooling sequence with realistic physics for WD cooling timescales. This work provides a large grid of MESA models for carbon-oxygen core WDs with hydrogen atmospheres (spectral type DA/DC), descended from full prior stellar evolution calculations. The model tracks, isochrones, and WD cooling timescale contours are available on the MIST project website and at doi:10.5281/zenodo.15242047. Our WD models provide a very large, publicly available grid with detailed physics for WD cooling timescales: realistic interior and envelope compositions, with element diffusion and heavy-element sedimentation, nuclear burning at the base of the WD hydrogen envelope, core crystallization, and C/O phase separation. As a large grid of open-source stellar evolution models, these WD models provide both out-of-the-box model tracks for comparison with observations and a framework for building further WD models to investigate variations in WD physics.

We update and expand the MESA Isochrones and Stellar Tracks (MIST) database to include variations in the alpha-capture elements, specifically [alpha/Fe] = -0.2, 0, +0.2, +0.4, and +0.6 for the full range of -3 <= [Fe/H] <= +0.5 already covered by MIST. Variations in [alpha/Fe] are included in a self-consistent manner from the stellar interior models to the synthetic spectra used to translate these models in the observational plane. We describe a number of updates to the physics utilized in these models as well as new information provided by the models. We validate the models with comparisons to other stellar evolution models including the previous generation of MIST and other models from the literature. MIST data products including stellar evolution tracks, isochrones, and bolometric correction tables can be obtained from the MIST project website, https://mist.science. All necessary files to reproduce MIST models are available from Zenodo.

We present a systematic Bayesian search for chemical fingerprints of planet engulfment in 113 solar twins and analogs with high-precision abundance measurements, 45 of which host known or candidate planets or brown-dwarf companions. We constructed a Bayesian framework with three sets of abundance models: random scatter, Galactic chemical evolution, and planet engulfment with bulk Earth or CM chondrite compositions. Through model comparisons, we identified three candidates whose abundance patterns strongly favor planet engulfment over the alternatives, with inferred engulfed masses of about 7.5-33 Earth masses. Our findings correspond to a nominal detection rate of 1-3

Context. Convection and rotation are both key processes in stellar evolution modelling. While standard mixing-length theory (MLT) provides a widely used modelling of convection, it neglects the effects of rotation on convective transport. Aims. We investigate how rotating mixing-length theory (R-MLT), which accounts for the influence of rotation on convection, affects the internal structure, convective mixing, and angular momentum transport in stellar models in comparison to the standard non-rotating MLT. Methods. Using the MESA stellar structure and evolution software, we model the main-sequence evolution of a 5 M-circle dot star, for three cases: non-rotating, rotating with standard MLT for modelling convection, and rotating with R-MLT in convection zones, with the initial rotation rate set to 20 percent of the critical (Keplerian) value at the surface for the rotating models. Results. We find that R-MLT reduces both the convective velocity and mixing length in the stellar core, leading to a smaller convective diffusion coefficient and a similar to 20 percent reduction in the extent of the convective overshooting region. While the overall size of the convective core remains nearly unchanged, R-MLT changes the resulting chemical gradient at the core-envelope boundary, shifting the peak of the Brunt-Vaisala frequency and modifying the angular momentum transport in that region. Conclusions. Including the effects of rotation in the treatment of convection through R-MLT introduces measurable structural and transport differences, underscoring the importance of incorporating rotation-convection coupling in models of stars.

Context. Convection and rotation are both key processes in stellar evolution modelling. While standard mixing-length theory (MLT) provides a widely used modelling of convection, it neglects the effects of rotation on convective transport. Aims. We investigate how rotating mixing-length theory (R-MLT), which accounts for the influence of rotation on convection, affects the internal structure, convective mixing, and angular momentum transport in stellar models in comparison to the standard non-rotating MLT. Methods. Using the MESA stellar structure and evolution software, we model the main-sequence evolution of a 5 M⊙ star, for three cases: non-rotating, rotating with standard MLT for modelling convection, and rotating with R-MLT in convection zones, with the initial rotation rate set to 20 percent of the critical (Keplerian) value at the surface for the rotating models. Results. We find that R-MLT reduces both the convective velocity and mixing length in the stellar core, leading to a smaller convective diffusion coefficient and a ∼20 percent reduction in the extent of the convective overshooting region. While the overall size of the convective core remains nearly unchanged, R-MLT changes the resulting chemical gradient at the core–envelope boundary, shifting the peak of the Brunt–Väisälä frequency and modifying the angular momentum transport in that region. Conclusions. Including the effects of rotation in the treatment of convection through R-MLT introduces measurable structural and transport differences, underscoring the importance of incorporating rotation–convection coupling in models of stars.

We present a novel nuclear network implementation, GridFire, which has been developed with a focus on efficiency, ease of use, and automatic physical extension. In this first paper we provide a detailed overview of GridFire's numerics, performance characteristics, and a comparison to pre-existing nuclear network implementations pynucastro and MESA's net module. We find that generally GridFire performs similarly to and requires significantly less user input and setup than these current generation nuclear network codes. Further, GridFire has been developed with a flexible "view" based physics engine that allowing researchers to implement domain specific physics without modifying the underlying source code. GridFire has been released under an open-source license, GPL v3.0, and will eventually be incorporated into the forthcoming 4D-STAR stellar structure evolution code.

We present new stellar population models, alpha-MC, self-consistently taking into account nonsolar [alpha/Fe] abundances for both isochrones and stellar spectra. The alpha-MC models are based on alpha-enhanced MIST isochrones and C3K spectral libraries, which are publicly available in FSPS. Our new models cover a wide range of ages ( log(age/yr)=5.0-10.3 ), metallicities ([Fe/H] = [-2.5, +0.5] in steps of 0.25, [alpha/Fe] = -0.2, +0.0, +0.2, +0.4, +0.6), and wavelengths (0.1-2.5 mu m). We investigate the separate and combined effects of alpha-enhanced isochrones and stellar spectral libraries on simple stellar populations, including their broadband colors, spectral indices, and full spectra. We find that the primary effect of alpha-enhancement in isochrones is to lower the overall continuum levels and redden the continuum shapes, while alpha-enhancement in stellar spectra mainly affects individual spectral lines. At constant [Fe/H], alpha-enhancement has significant impacts on the broadband colors by similar to 0.1-0.4 mag across all ages (0.01-10 Gyr). The effects of alpha-enhancement on colors at fixed [Z/H] are smaller, by similar to 0.1-0.2 mag. The spectral indices involving alpha-elements, Ca4227 and Mg b, increase with [alpha/Fe] (both at fixed [Fe/H] and fixed [Z/H]) due to enhanced alpha-abundances. At constant [Fe/H], alpha-enhancement weakens most Fe-sensitive and hydrogen Balmer lines. Our new self-consistent alpha-enhanced models will be essential in deriving accurate physical properties of high-redshift galaxies, where alpha-enhancement is expected to be common.

CASTOR is a proposed wide-field (30 ' x30 '=0.25 deg(2)), high-resolution (FWHM similar to 0.15 ''), 1-m-diameter space telescope that is under development by the Canadian Space Agency and the National Research Council of Canada. Optimized for UV/blue-optical wavelengths, the telescope uses dichroics to enable imaging in three channels (and up to five bands) that cover the 0.15 to 0.55 mu m spectral region, simultaneously. CASTOR will also feature low- and low-medium-resolution spectroscopic capabilities through the use of a deployable grism for low-resolution (R less than or similar to 420) slit-less spectroscopy in its UV and u channels, and low-medium-resolution R similar to 1400 multi-object spectroscopy in a parallel field using a digital micro-mirror device. High-speed, precision photometry will be possible using dedicated CMOS detectors in each of its three channels. We present an overview of the mission, including the optical design, instruments and detectors, payload layout, satellite bus, orbit, and ground segment. We describe the mission's scientific capabilities and expected place within the astronomical landscape in the 2030s. The 5-year lifetime is baselined on a combination of legacy surveys, guest observer programs, and target-of-opportunity science. We summarize scientific plans for the mission in each of eight fields: cosmology, time domain and multi-messenger science, active galactic nuclei, galaxies, near-field cosmology, stellar astrophysics, exoplanets, and solar system studies. We conclude by describing ongoing development efforts, highlighting areas of particular relevance for NASA's Habitable Worlds Observatory.

Whether considering rare astrophysical events on cosmological scales or unresolved stellar populations, accurate models must account for the integrated contribution from the entire history of star formation upon which that population is built. Here, we describe the second version of POSYDON , an open-source binary population synthesis code based on extensive grids of detailed binary evolution models computed using the MESA code, which follows both stars’ structures as a binary system evolves through its complete evolution from the zero-age main sequence, through multiple phases of mass transfer and supernovae, to their death as compact objects. To generate synthetic binary populations, POSYDON uses advanced methods to interpolate between our large, densely spaced grids of simulated binaries. In our updated version of POSYDON , we account for the evolution of stellar binaries across a cosmological range of metallicities, extending from 10 ^−4 to 2 Z _⊙ , including grids specifically focused on the Small and Large Magellanic Clouds (0.2 and 0.45 Z _⊙ ). In addition to describing our model grids and detailing our methodology, we outline several improvements to POSYDON . These include the incorporation of single stars in stellar populations, a treatment for stellar mergers, and a careful modeling of “reverse-mass transferring” binaries in which a once-accreting star later becomes a donor star. Our simulations are focused on binaries with at least one high-mass component, such as those that host neutron stars and black holes, and we provide postprocessing methods to account for the cosmological evolution of metallicity and star formation as well as rate calculations for transient events.

From >1000 orbits of HST imaging, we present deep homogeneous resolved star color–magnitude diagrams that reach the oldest main-sequence turnoff and uniformly measured star formation histories (SFHs) of 36 dwarf galaxies (−6 ≥ M V ≥ −17) associated with the M31 halo, and for 10 additional fields in M31, M33, and the Giant Stellar Stream. From our SFHs, we find: (i) The median stellar age and quenching epoch of M31 satellites correlate with galaxy luminosity and galactocentric distance. Satellite luminosity and present-day distance from M31 predict the satellite quenching epoch to within 1.8 Gyr at all epochs. This tight relationship highlights the fundamental connection between satellite halo mass, environmental history, and star formation duration. (ii) There is no difference between the median SFH of galaxies on and off the great plane of Andromeda satellites. (iii) ~50% of our M31 satellites show prominent ancient star formation (>12 Gyr ago) followed by delayed quenching (8–10 Gyr ago), which is not commonly observed among the MW satellites. (iv) A comparison with TNG50 and FIRE-2 simulated satellite dwarfs around M31-like hosts shows that some of these trends (dependence of SFH on satellite luminosity) are reproduced in the simulations while others (dependence of SFH on galactocentric distance, presence of the delayed-quenching population) are weaker or absent. We provide all photometric catalogs and SFHs as High-Level Science Products on MAST.

We present brutus, an open source Python package for quickly deriving stellar properties, distances, and reddenings to stars based on grids of stellar models constrained by photometric and astrometric data. We outline the statistical framework for deriving these quantities, its implementation, and various Galactic priors over the 3-D distribution of stars, stellar properties, and dust extinction (including R_V variation). We establish a procedure to empirically calibrate MIST v1.2 isochrones by using open clusters to derive corrections to the effective temperatures and radii of the isochrones, which reduces systematic errors on the lower main sequence. We also describe and apply a method to estimate photometric offsets between stellar models and observed data using nearby, low-reddening field stars. We perform a series of tests on mock and real data to examine parameter recovery with MIST under different modeling assumptions, illustrating that brutus is able to recover distances and other stellar properties using optical to near-infrared photometry and astrometry. The code is publicly available at https://github.com/joshspeagle/brutus.

We present an analysis of high-resolution optical spectra recorded for 30 stars of the split extended main-sequence turnoff of the young (similar to 40 Myr) Small Magellanic Cloud globular cluster NGC 330. Spectra were obtained with the Michigan/Magellan Fiber System and Magellan Inamori Kyocera Echelle spectrographs located on the Magellan-Clay 6.5 m telescope. These spectra revealed the presence of Be stars, occupying primarily the cool side of the split main sequence. Rotational velocity (v sin i) measurements for most of the targets are consistent with the presence of two populations of stars in the cluster: one made up of rapidly rotating Be stars (< v sin i > approximate to 200 km s(-1)) and the other consisting of warmer stars with slower rotation (< v sin i > approximate to 50 km s(-1)). Core emission in the H delta photospheric lines was observed for most of the H alpha emitters. The shell parameter computed for the targets in our sample indicates that most of the observed stars should have inclinations below 75 degrees. These results confirm the detection of Be stars obtained through photometry but also reveal the presence of narrow H alpha and H delta features for some targets that cannot be detected with low-resolution spectroscopy or photometry. Asymmetry variability of H alpha line profiles on the timescales of a few years is also observed and could provide information on the geometry of the decretion disks. Observations revealed the presence of nebular H alpha emission, strong enough in faint targets to compromise the extraction of spectra and to impact narrow-band photometry used to assess the presence of H alpha emission.

We present NIRCam and NIRISS modules for DOLPHOT, a widely-used crowded field stellar photometry package. We describe details of the modules including pixel masking, astrometric alignment, star finding, photometry, catalog creation, and artificial star tests (ASTs). We tested these modules using NIRCam and NIRISS images of M92 (a Milky Way globular cluster), Draco II (an ultra-faint dwarf galaxy), and WLM (a star-forming dwarf galaxy). DOLPHOT's photometry is highly precise and the color-magnitude diagrams are deeper and have better definition than anticipated during original program design in 2017. The primary systematic uncertainties in DOLPHOT's photometry arise from mismatches in the model and observed point spread functions (PSFs) and aperture corrections, each contributing $\lesssim0.01$ mag to the photometric error budget. Version 1.2 of WebbPSF models, which include charge diffusion and interpixel capacitance effects, significantly reduced PSF-related uncertainties. We also observed minor ($\lesssim0.05$ mag) chip-to-chip variations in NIRCam's zero points, which will be addressed by the JWST flux calibration program. Globular cluster observations are crucial for photometric calibration. Temporal variations in the photometry are generally $\lesssim0.01$ mag, although rare large misalignment events can introduce errors up to 0.08 mag. We provide recommended DOLPHOT parameters, guidelines for photometric reduction, and advice for improved observing strategies. Our ERS DOLPHOT data products are available on MAST, complemented by comprehensive online documentation and tutorials for using DOLPHOT with JWST imaging data.

We present age estimates for over 8100 subgiant branch (SGB) stars in Omega Centauri (omega Cen) to study its star formation history. Our large data set, which combines multi-wavelength Hubble Space Telescope photometry with MUSE metallicities, provides an unprecedented opportunity to measure individual stellar ages. We do this by fitting each star's photometry and metallicity with theoretical isochrones that are embedded with an empirical [C + N + O]-[Fe/H] relation specific to omega Cen. The bulk of the stars have ages between 13 and 10 Gyr, with the mean stellar age being 12.08 +/- 0.01 Gyr and the median age uncertainty being 0.68 Gyr. From these ages we construct the most complete age-metallicity relation for omega Cen to date. We find that the mean age of stars decreases with increasing metallicity and find two distinct streams in the age-metallicity plane, hinting at different star formation pathways. We derive an intrinsic spread in the ages of 0.75 +/- 0.01 Gyr for the whole cluster, with the age spread showing a clear increase with metallicity. We verify the robustness of our age estimations by varying isochrone parameters and constraining our systematics. We find the C + N + O relation to be the most critical consideration for constraining the age-metallicity relation. We also present an SGB chromosome map with age information. In the future these stellar ages could be combined with chemical abundances to study age differences in subpopulations and uncover the chemical evolution history of this massive nuclear star cluster.

We present the first spectroscopic estimates of the chemical abundance of M dwarf stars in a globular cluster (GC), namely 47 Tucanae. By exploiting NIRSpec on board the James Webb Space Telescope, we gathered low-resolution spectra for 28 stars with masses in the range ∼0.4–0.5 M ⊙. The spectra are strongly affected by the H2O water vapor bands, which can be used as indicators of oxygen abundance. The spectral analysis reveals that the target stars feature a different O abundance, with a difference of ∼0.40 dex between the first and the most polluted second population. The observed range is similar to that observed among red giant stars. This result reinforces previous findings based on the analysis of photometric diagrams, including the “chromosome maps,” providing a first, and more direct, evidence of light element variations in the M dwarfs’ mass regime. The observation that the multiple populations, with their variations in light elements, exhibit the same patterns from the lower main sequence all the way to the red giant branch further strengthens the notion that multiple stellar populations in GCs formed in a series of bursts of star formation.

Neutron star – black hole (NSBH) merger events bring us new opportunities to constrain theories of stellar and binary evolution and understand the nature of compact objects. In this work, we investigated the formation of merging NSBH binaries at solar metallicity by performing a binary population synthesis study of merging NSBH binaries with the newly developed code POSYDON. The latter incorporates extensive grids of detailed single and binary evolution models, covering the entire evolution of a double compact object progenitor. We explored the evolution of NSBHs originating from different formation channels, which in some cases differ from earlier studies performed with rapid binary population synthesis codes. In this paper, we present the population properties of merging NSBH systems and their progenitors such as component masses, orbital features, and BH spins, and we detail our investigation of the model uncertainties in our treatment of common envelope (CE) evolution and the core-collapse process. We find that at solar metallicity, under the default model assumptions, most of the merging NSBHs have BH masses in the range of 3 − 11 M⊙ and chirp masses within 1.5 − 4 M⊙. Independently of our model variations, the BH always forms first with dimensionless spin parameter ≲0.2, which is correlated to the initial binary orbital period. Some BHs can subsequently spin up moderately (χBH ≲ 0.4) due to mass transfer, which we assume to be Eddington limited. Binaries that experience CE evolution rarely demonstrate large tilt angles. Conversely, approximately 40% of the binaries that undergo only stable mass transfer without CE evolution contain an anti-aligned BH. Finally, accounting for uncertainties in both the population modeling and the NS equation of state, we find that 0 − 18.6% of NSBH mergers may be accompanied by an electromagnetic counterpart.

The James Webb Space Telescope (JWST) observations have been demonstrated to be efficient in detecting globular clusters' (GCs) multiple stellar populations in the low mass regime of M dwarfs. We present an overview, and first results, of different projects that can be explored by using the JWST observations gathered under the GO2560 for 47 Tucanae, a first program entirely devoted to the investigation of multiple populations in very low mass stars, which includes spectroscopic data for the faintest GC stars for which spectra are available. Our color-magnitude diagram (CMD) shows some substructures for ultracool stars, including gaps and breaks in slope. In particular, we observe both a gap and a minimum in the F322W2 luminosity function less than one magnitude apart, and discuss which one could be associated with the H-burning limit. We detect stars fainter than this minimum, very likely the brown dwarfs. We corroborate the ubiquity of the multiple populations across different masses, from ~0.1 solar masses up to red giants (~0.8 solar masses). The oxygen range inferred from the M dwarfs, both from the CMD and from the spectra of two M dwarfs associated with different populations, is similar to that observed in giants. We have not detected any difference between the fractions of stars in distinct populations across stellar masses >~0.1 solar masses. This work demonstrates the JWST's capability in uncovering multiple populations within M dwarfs and illustrates the possibility to analyse very low-mass stars in GCs approaching the H-burning limit and the brown-dwarf sequence.

Stellar chemical compositions can be altered by ingestion of planetary material1,2 and/or planet formation, which removes refractory material from the protostellar disk3,4. These 'planet signatures' appear as correlations between elemental abundance differences and the dust condensation temperature3,5,6. Detecting these planet signatures, however, is challenging owing to unknown occurrence rates, small amplitudes and heterogeneous star samples with large differences in stellar ages7,8. Therefore, stars born together (that is, co-natal) with identical compositions can facilitate the detection of planet signatures. Although previous spectroscopic studies have been limited to a small number of binary stars9-13, the Gaia satellite14 provides opportunities for detecting stellar chemical signatures of planets among co-moving pairs of stars confirmed to be co-natal15,16. Here we report high-precision chemical abundances for a homogeneous sample of ninety-one co-natal pairs of stars with a well defined selection function and identify at least seven instances of planetary ingestion, corresponding to an occurrence rate of eight per cent. An independent Bayesian indicator is deployed, which can effectively disentangle the planet signatures from other factors, such as random abundance variation and atomic diffusion17. Our study provides evidence of planet signatures and facilitates a deeper understanding of the star-planet-chemistry connection by providing observational constraints on the mechanisms of planet engulfment, formation and evolution. By analysing the chemical abundance differences of pairs of co-moving stars born together, it is found that about 8% show chemical signatures that indicate ingestion of planetary material.

We present Augustus , a catalog of distance, extinction, and stellar parameter estimates for 170 million stars from 14 mag < r < 20 mag and with ∣ b ∣ > 10° drawing on a combination of optical to near-infrared photometry from Pan-STARRS, 2MASS, UKIDSS, and unWISE along with parallax measurements from Gaia DR2 and 3D dust extinction maps. After applying quality cuts, we find 125 million objects have “high-quality” posteriors with statistical distance uncertainties of ≲10% for objects with well-constrained stellar types. This is a substantial improvement over the distance estimates derived from Gaia parallaxes alone and in line with the recent results from Anders et al. We find the fits are able to reproduce the dereddened Gaia color–magnitude diagram accurately, which serves as a useful consistency check of our results. We show that we are able to detect large, kinematically coherent substructures in our data clearly relative to the input priors, including the Monoceros Ring and the Sagittarius Stream, attesting to the quality of the catalog. Our results are publicly available at doi: 10.7910/DVN/WYMSXV . An accompanying interactive visualization can be found at http://allsky.s3-website.us-east-2.amazonaws.com .

Context. Ultra-luminous X-ray sources (ULXs) are sources observed to have extreme X-ray luminosities exceeding the Eddington limit of a stellar-mass black hole (BH). A fraction of ULXs show X-ray pulsations, which are evidence for accreting neutron stars (NSs). Theoretical studies have suggested that NSs, rather than BHs, dominate the compact objects of intrinsic ULX populations, even though the majority of the observed sample is non-pulsating, implying that X-ray pulses from many NS ULXs are unobservable. Aims. We simulate populations of X-ray binaries covering a range of starburst ages spanning from 5 to 1000 Myr with the aim of comparing the properties of observed ULXs at the different ages. Additionally, we compare two models describing different assumptions for the physical processes governing binary evolution. Methods. We used the new population synthesis code POSYDON to generate multiple populations of ULXs spanning multiple burst ages. We employed a model for geometrically beamed emission from a super-Eddington accretion disk in order to estimate the luminosities of ULXs. Following theoretical predictions for the alignment of the spin axis of an NS with the accretion disk due to mass transfer, we estimated the required mass to be accreted by the NSs in the ULX populations so that the alignment suppresses observable X-ray pulses. Results. While we find that the properties of ULX populations are sensitive to model assumptions, there are certain trends that the populations follow. Generally, young and old stellar populations are dominated by BH and NS accretors, respectively. The donor stars go from being massive H-rich main-sequence stars in young populations (< 100 Myr) to low-mass post-main sequence H-rich stars in older populations (> 100 Myr), with stripped He-rich giant donors dominating the populations at around 100 Myr. In addition, we find that NS ULXs exhibit stronger geometrical beaming than BH ULXs, leading to an underrepresentation of NS accretors in observed populations. Coupled with our finding that X-ray pulses are suppressed in at least 60% of the NS ULXs, we suggest that the observed fraction of ULXs with detectable X-ray pulses is very small, in agreement with observations. Conclusions. We show that geometrical beaming and the mass-accretion phase are critical aspects of understanding ULX observations. Our results suggest that even though most ULXs have accreting NSs, those with observable X-ray pulses would be very few.