Sample Of Stars Research Articles

Lithium Abundances from the LAMOST Medium-resolution Survey Data Release 9

Lithium is a fragile but crucial chemical element in the Universe, and exhibits interesting and complex behaviors. Thanks to the mass of spectroscopic data from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) medium-resolution survey (MRS), we can investigate the lithium abundances in a large and diverse sample of stars, which could bring vital help in studying the origin and evolution of lithium. In this work, we use the Li i 6707.8 Å line to derive the lithium abundance through a template-matching method. A catalog of precise lithium abundance is presented for 795,384 spectra corresponding to 455,752 stars from the LAMOST MRS Data Release 9. Comparing our results with those of external high-resolution references, we find good consistency with a typical deviation of σ A(Li) ∼ 0.2 dex. We also analyze the internal errors using stars that have multiple LAMOST MRS observations, which will reach as low as 0.1 dex when the signal-to-noise ratio of the spectra is >20. Besides, our result indicates that a small fraction of giant stars still exhibit a surprisingly high lithium content, and 967 stars are identified as Li-rich giants with A(Li) > 1.5 dex, accounting for ∼2.6% of our samples. If one takes into account the fact that nearly all stars deplete lithium during the main sequence, then the fraction of Li-rich stars may far exceed 2.6%. This new catalog covers a wide range of stellar evolutionary stages from pre-main sequence to giants, and will provide help to the further study of the chemical evolution of lithium.

On the Performances of Estimating Stellar Atmospheric Parameters from CSST Broad-band Photometry

Deriving atmospheric parameters of a large sample of stars is of vital importance to understand the formation and evolution of the Milky Way. Photometric surveys, especially those with near-ultraviolet filters, can offer accurate measurements of stellar parameters, with the precision comparable to that from low/medium resolution spectroscopy. In this study, we explore the capability of measuring stellar atmospheric parameters from Chinese Space Station Telescope (CSST) broad-band photometry (particularly in the near-ultraviolet bands), based on synthetic colors derived from model spectra. We find that colors from the optical and near-ultraviolet filter systems adopted by CSST show significant sensitivities to the stellar atmospheric parameters, especially the metallicity. According to our mock data tests, the precision of the photometric metallicity is quite high, with typical values of 0.17 and 0.20 dex for dwarf and giant stars, respectively. The precision of the effective temperature estimated from broad-band colors are within 50 K.

Evolved Massive Stars at Low Metallicity. VII. The Lower Mass Limit of the Red Supergiant Population in the Large Magellanic Cloud

The precise definition of the lower mass limit of red supergiant stars (RSGs) is an open question in astrophysics and does not attract much attention. Here, we assemble a spectroscopic evolved cool star sample with 6602 targets, including RSGs, asymptotic giant branch stars, and red giant branch stars, in the Large Magellanic Cloud based on Gaia DR3 and Sloan Digital Sky Survey IV/APOGEE-2. The reference spectrum of each stellar population is built according to the quantile range of relative intensity (1% ∼ 99%). Five different methods, e.g., χ 2, cosine similarity, machine learning (ML), equivalent width, and line ratio, are used in order to separate different stellar populations. ML and χ 2 provide the best and relatively consistent prediction of a certain population. The derived lower limit of the RSG population is able to reach the K s -band tip of the red giant branch (K s ≈12.0 mag), indicating a luminosity as low as about 103.5 L ⊙, which corresponds to a stellar radius of only about 100 R ⊙. Given the mass–luminosity relation of L/L⊙=f(M/M⊙)3 with f ≈ 15.5 ± 3 and taking into account the mass loss of faint RSGs up to now, the minimal initial mass of the RSG population would be about 6.1 ± 0.4 M ⊙, which is much lower than the traditional threshold of 8 M ⊙ for the massive stars. This is the first spectroscopic evidence, indicating that the lower mass limit of the RSG population is around 6 M ⊙. However, the destinies of such faint RSGs are still elusive and may have a large impact on stellar evolutionary and supernova models.

At least one in a dozen stars shows evidence of planetary ingestion.

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.

A 500 pc volume-limited sample of hot subluminous stars. I. Space density, scale height, and population properties

We present the first volume-limited sample of spectroscopically confirmed hot subluminous stars out to 500 pc, defined using the accurate parallax measurements from the Gaia space mission data release 3 (DR3). The sample comprises a total of 397 members, with 305 ($ 77<!PCT!>$) identified as hot subdwarf stars, including 83 newly discovered systems. Of these, we observe that 178 ($ are hydrogen-rich sdBs, 65 are sdOBs ($ 21<!PCT!>$), 32 are sdOs ($ 11<!PCT!>$), and 30 are He-sdO/Bs ($ 10<!PCT!>$). Among them, 48 ($ 16<!PCT!>$) exhibit an infrared excess in their spectral energy distribution fits, suggesting a composite binary system. The hot subdwarf population is estimated to be 90<!PCT!> complete, assuming that most missing systems are these composite binaries located within the main sequence (MS) in the Gaia colour-magnitude diagram (CMD). The remaining sources in the sample include cataclysmic variables (CVs), blue horizontal branch stars (BHBs), hot white dwarfs (WDs), and MS stars. We derived the mid-plane density $ $ and scale height $ h z $ for the non-composite hot subdwarf star population using a hyperbolic sechant profile (sech$^2$). The best-fit values are $ $ stars/pc3 and $ h z 62$ pc. When accounting for the composite-colour hot subdwarfs and their estimated completeness, the mid-plane density increases to $ $ stars/pc3. This corrected space density is an order of magnitude lower than predicted by population synthesis studies, supporting previous observational estimates.

African Star Apple Juice Stored at Tropical Ambient and Refrigeration Temperatures: Effect on Physicochemical Characteristics, Antioxidant Properties and Microbiological

The present study was aimed at evaluating the physicochemical and antioxidant properties as well as microbiological quality of extracted juice from African star apple (Chrysophyllum albidum) stored under tropical ambient and refrigeration conditions. Juice was extracted from mashed star apple fruit cotyledons (after deseeding) and pasteurized in a water bath at 71.2 oC for 30 minutes before storage for four (4) weeks under tropical ambient (28±2 oC) and refrigeration (6±2 oC) conditions. The results showed that there was no fibre in the juice, the moisture was 78.51% and 79.13% for fresh African star apple (ASA) juice and sample stored under ambient conditions, respectively. It also showed pH of ASA juice at week 0 to be 3.52 and week 4 for both samples stored at refrigeration and ambient temperatures to be 2.85 and 2.28, respectively. There was no fecal coliform count in all the studied juice samples throughout the storage period, but total viable bacteria counts were 2.7x104 cfu/ml, 1.84x105 cfu/ml and 6.6x104 cfu/ml for fresh juice and juice stored for 4 weeks at ambient temperature and refrigeration conditions, respectively. Overall, storage conditions had insignificant impact on the antioxidant properties and free radical scavenging capacity of the fruit juice; the slight changes observed were linked to usual molecular reactions. In conclusion, storage under refrigeration conditions elongated the shelf life of the juice.

K2 results for “young” α-rich stars in the Galaxy

Context. The origin of apparently young α-rich stars in the Galaxy is still a matter of debate in Galactic archaeology, whether they are genuinely young or might be products of binary evolution, and mergers or mass accretion. Aims. Our aim is to shed light on the nature of young α-rich stars in the Milky Way by studying their distribution in the Galaxy thanks to an unprecedented sample of giant stars that cover different Galactic regions and have precise asteroseismic ages, and chemical and kinematic measurements. Methods. We analyzed a new sample of ∼6000 stars with precise ages coming from asteroseismology. Our sample combines the global asteroseismic parameters measured from light curves obtained by the K2 mission with stellar parameters and chemical abundances obtained from APOGEE DR17 and GALAH DR3, then cross-matched with Gaia DR3. We define our sample of young α-rich stars and study their chemical, kinematic, and age properties. Results. We investigated young α-rich stars in different parts of the Galaxy and we find that the fraction of young α-rich stars remains constant with respect to the number of high-α stars at ∼10%. Furthermore, young α-rich stars have kinematic and chemical properties similar to high-α stars, except for [C/N] ratios. Conclusions. Thanks to our new K2 sample, we conclude that young α-rich stars have similar occurrence rates in different parts of the Galaxy, and that they share properties similar to the normal high-α population, except for [C/N] ratios. This suggests that these stars are not genuinely young, but are products of binary evolution, and mergers or mass accretion. Under that assumption, we find the fraction of these stars in the field to be similar to that found recently in clusters. This suggests that ∼10% of the low-α field stars could also have their ages underestimated by asteroseismology. This should be kept in mind when using asteroseismic ages to interpret results in Galactic archaeology.

Stellar Population Astrophysics (SPA) with TNG

Context. The age, evolution, and chemical properties of the Galactic disk can be effectively ascertained using open clusters. Within the large program Stellar Populations Astrophysics at the Telescopio Nazionale Galileo, we specifically focused on stars in open clusters, to investigate various astrophysical topics, from the chemical content of very young systems to the abundance patterns of lesser studied intermediate-age and old open clusters. Aims. We investigate the astrophysically interesting element fluorine (F), which has an uncertain and intriguing cosmic origin. We also determine the abundance of cerium (Ce), as F abundance is expected to correlate with the s-process elements. We intend to determine the trend of F abundance across the Galactic disk as a function of metallicity and age. This will offer insights into Galactic chemical evolution models, potentially enhancing our comprehension of this element’s cosmic origin. Methods. High-resolution near-infrared spectra were obtained using the GIANO-B spectrograph. The Python version of Spectroscopy Made Easy (PySME), was used to derive atmospheric parameters and abundances. The stellar parameters were determined using OH, CN, and CO molecular lines along with Fe I lines. The F and Ce abundances were inferred using two K-band HF lines (λλ 2.28, 2.33 µm) and two atomic H-band lines (λλ 1.66, and 1.71 µm), respectively. Results. Of all the clusters in our sample, only King 11 had not been previously studied through medium- to high-resolution spectroscopy, and our stellar parameter and metallicity findings align well with those documented in the literature. We have successfully inferred F and Ce abundances in all seven open clusters and probed the radial and age distributions of abundance ratios. This paper presents the first F Galactic radial abundance gradient. Our results are also compared with literature estimates and with Galactic chemical evolution models that have been generated using different F production channels. Conclusions. Our results indicate a constant, solar pattern in the [F/Fe] ratios across clusters of different ages, supporting the latest findings that fluorine levels do not exhibit any secondary behavior for stars with solar or above-solar metallicity. However, an exception to this trend is seen in NGC 6791, a metal-rich, ancient cluster whose chemical composition is distinct due to its enhanced fluorine abundance. This anomaly strengthens the hypothesis that NGC 6791 originated in the inner regions of the Galaxy before migrating to its present position. By comparing our sample stars with the predictions of Galactic chemical evolution models, we came to the conclusion that both asymptotic giant branch stars and massive stars, including a fraction of fast rotators that increase with decreasing metallicity, are needed to explain the cosmic origin of F.

The Gaia RVS benchmark stars

Context. The Gaia satellite has already provided the astronomical community with three data releases, and the Radial Velocity Spectrometer (RVS) on board Gaia has provided the radial velocity for 33 million stars. Aims. When deriving the radial velocity from the RVS spectra, several stars are measured to have large values. To verify the credibility of these measurements, we selected some bright stars with the modulus of radial velocity in excess of 500 km s−1 to be observed with SOPHIE at OHP and UVES at VLT. This paper is devoted to investigating the chemical composition of the stars observed with UVES. Methods. We derived atmospheric parameters using Gaia photometry and parallaxes, and we performed a chemical analysis using the MyGIsFOS code. Results. We find that the sample consists of metal-poor stars, although none have extremely low metallicities. The abundance patterns match what has been found in other samples of metal-poor stars selected irrespective of their radial velocities. We highlight the presence of three stars with low Cu and Zn abundances that are likely descendants of pair-instability supernovae. Two stars are apparently younger than 1 Ga, and their masses exceed twice the turn-off mass of metal-poor populations. This makes it unlikely that they are blue stragglers because it would imply they formed from triple or multiple systems. We suggest instead that they are young metal-poor stars accreted from a dwarf galaxy. Finally, we find that the star RVS721 is associated with the Gjoll stream, which itself is associated with the Globular Cluster NGC 3201.

Density discrepancy between transit-timing variations and radial velocity: Insights from the host star composition

Context. The determination of planetary densities from the masses derived with the radial velocity (RV) and transit-timing variation (TTV) methods reveals discrepancies. Specifically, planets detected through RV exhibit higher densities than those detected through TTV, even though their radii are similar. Understanding the origins of these discrepancies is crucial and timely, especially with upcoming ground- and space-based missions dedicated to exoplanet research. Aims. We explored the possibility that the discrepant mass/densities in the TTV and RV populations might be linked to the properties of the environments in which these planets are formed. Methods. For the largest currently available sample of FGK-type stars hosting low-mass TTV and RV planets, we determined the host star abundances. Then, by employing a simple stoichiometric model, we used these abundances to estimate the iron-to-silicate mass fraction (firon) and the water-mass fraction (wf) of the protoplanetary disks. We also calculated the kinematic properties of the host stars. Results. We observed an indication that the hosts of TTV planets have slightly higher firon and lower wf values than their RV counterparts. This suggests that TTV planets (without considering their atmospheres) are denser than RV planets on average, which implies that larger atmospheres on TTV planets are required to account for their overall lower densities. However, we also note differences in the properties of the planets, such as their orbital periods, and variations in the quality of the spectroscopic data, which may have an impact on these results. Conclusions. Exploring the TTV-RV mass and/or density discrepancy through a chemical analysis of the host star holds promise for future research, particularly with larger sample sizes and higher-quality data. Meanwhile, the provided detailed host star abundances can be employed to study the composition of the planets within the current sample, thereby contributing to a better understanding of the aforementioned discrepancy.

Gaia’s brightest very metal-poor (VMP) stars

Context. Gaia DR3 has offered the scientific community a remarkable dataset of approximately one million spectra acquired with the radial velocity spectrometer (RVS) in the calcium II triplet region, which is well suited to identify very metal-poor (VMP) stars. However, over 40% of these spectra have no released parameters by Gaia’s GSP-Spec pipeline in the domain of VMP stars, whereas VMP stars are key tracers of early Galactic evolution. Aims. We aim to provide spectroscopic metallicities for VMP stars using Gaia RVS spectra, thereby producing a catalogue of bright VMP stars distributed over the full sky that can serve as the basis for studies of early chemical evolution throughout the Galaxy. Methods. We selected VMP stars using photometric metallicities from the literature and analysed the Gaia RVS spectra to infer spectroscopic metallicities for these stars. Results. The inferred metallicities agree very well with literature high-resolution metallicities, with a median systematic offset of 0.1 dex and standard deviation of ∼0.15 dex. The purity of this sample in the VMP regime is ∼80%, with outliers representing a mere ∼3%. Conclusions. We have built an all-sky catalogue of ∼1500 stars available, featuring reliable spectroscopic metallicities down to [Fe/H] ∼ −4.0, of which ∼1000 are VMP stars. More than 75% of these stars have either no spectroscopic metallicity value in the literature to date or have been flagged as unreliable in their literature spectroscopic metallicity estimates. This catalogue of bright (G < 13) VMP stars is three times larger than the current sample of well-studied VMP stars in the literature in this magnitude range, making it ideal for high-resolution spectroscopic follow-ups and studies of the properties of VMP stars in different parts of our Galaxy.

Hints of a disrupted binary dwarf galaxy in the Sagittarius stream

ABSTRACT In this work, we look for evidence of a non-unity mass ratio binary dwarf galaxy merger in the Sagittarius stream. Simulations of such a merger show that, upon merging with a host, particles from the less massive galaxy will often mostly be found in the extended stream and less so in the central remnant. Motivated by these simulations, we use the Apache Point Observatory Galactic Evolution Experiment Data Release 17 chemical data from approximately 1100 stars in both the Sagittarius remnant and stream to look for evidence of contamination from a second dwarf galaxy. We separate the Sagittarius data into its remnant and stream and compare the [Mg/Fe] content of the two populations. In particular, we select [Mg/Fe] to search for hints of unique star formation histories among our sample stars. Comparing the stream and remnant populations, we find regions that have distinct [Mg/Fe] distributions for fixed [Fe/H], in addition to distinct chemical tracks in [Mg/Fe]–[Fe/H] abundance space. We show that there are large regions of the tracks for which the probability of the two samples being drawn from the same distribution is very low (p < 0.05). Furthermore, we show that the two tracks can be fit with unique star formation histories using simple, one-zone galactic chemical evolution models. While more work must be done to discern whether the hypothesis presented here is true, our work hints at the possibility that Sagittarius may consist of two dwarf galaxy progenitors.

Metallicity Distribution in the LMC and the SMC Based on the Tip-RGB Colors

The color index (J − K)0 of tip-red-giant branch (TRGB) is used to study the metallicity distribution in the Large and Small Magellanic Cloud. With the most complete and pure sample of red member stars so far, the areas are divided into 154 and 70 bins for the LMC and SMC, respectively, with similar number of stars by the Voronoi binning. For each bin, the position of TRGB on the near-infrared color–magnitude diagram, specifically (J − K)0/K 0, is determined by the poison-noise weighted method. Converting the color index of TRGB into metallicity, the metallicity gradients in the LMC and the SMC are obtained in four major directions. For the LMC, the gradient to the north is −0.006 ± 0.004 dex kpc−1, to the south −0.010 ± 0.005 dex kpc−1, to the east −0.006 ± 0.003 dex kpc−1, and to the west −0.010 ± 0.003 dex kpc−1. The farthest distance extends to 16 kpc. For the SMC, the gradients to the north, south, east, and west are −0.017 ± 0.031 dex kpc−1, −0.016 ± 0.007 dex kpc−1, −0.003 ± 0.002 dex kpc−1, and −0.004 ± 0.003 dex kpc−1, respectively. The farthest distance for the SMC extends to 27 kpc. The gradient is large from the center to 1 kpc.

Constructing the three-dimensional extinction density maps using V-net

ABSTRACT One of the major challenges we face is how to quickly and accurately create the three-dimensional (3D) density distributions of interstellar dust in the Milky Way using extinction and distance measurements of large samples of stars. In this study, we introduce a novel machine-learning approach that utilizes a convolution neural network, specifically a V-net, to infer the 3D distribution of dust density. Experiments are performed within two regions located towards the Galactic anticentre. The neural network is trained and tested using 10 000 simulations of dust density and line-of-sight extinction maps. Evaluation of the test sample confirms the successful generation of dust density maps from extinction maps by our model. Additionally, the performance of the trained network is evaluated using data from the literature. Our results demonstrate that our model is capable of capturing detailed dust density variations and can recover dust density maps while reducing the ‘fingers of god’ effect. Moving forward, we plan to apply this model to real observational data to obtain the fine distribution of dust at large and small scales in the Milky Way.

Stellar Cruise Control: Weakened Magnetic Braking Leads to Sustained Rapid Rotation of Old Stars

Despite a growing sample of precisely measured stellar rotation periods and ages, the strength of magnetic braking and the degree of departure from standard (Skumanich-like) spin-down have remained persistent questions, particularly for stars more evolved than the Sun. Rotation periods can be measured for stars older than the Sun by leveraging asteroseismology, enabling models to be tested against a larger sample of old field stars. Because asteroseismic measurements of rotation do not depend on starspot modulation, they avoid potential biases introduced by the need for a stellar dynamo to drive starspot production. Using a neural network trained on a grid of stellar evolution models and a hierarchical model-fitting approach, we constrain the onset of weakened magnetic braking (WMB). We find that a sample of stars with asteroseismically measured rotation periods and ages is consistent with models that depart from standard spin-down prior to reaching the evolutionary stage of the Sun. We test our approach using neural networks trained on model grids produced by separate stellar evolution codes with differing physical assumptions and find that the choices of grid physics can influence the inferred properties of the braking law. We identify the normalized critical Rossby number Rocrit/Ro⊙ = 0.91 ± 0.03 as the threshold for the departure from standard rotational evolution. This suggests that WMB poses challenges to gyrochronology for roughly half of the main-sequence lifetime of Sun-like stars.

Goodbye to Chi by Eye: A Bayesian Analysis of Photometric Binaries in Six Open Clusters

We present a robust methodology for identifying photometric binaries in star clusters. Using Gaia DR3, Pan-STARRS, and Two Micron All Sky Survey data, we self-consistently define the cluster parameters and binary demographics for the open clusters (OCs) NGC 2168 (M35), NGC 7789, NGC 6819, NGC 2682 (M67), NGC 188, and NGC 6791. These clusters span in age from ∼200 Myr (NGC 2168) to more than ∼8 Gyr (NGC 6791) and have all been extensively studied in the literature. We use the Bayesian Analysis of Stellar Evolution software suite to derive the age, distance, reddening, metallicity, binary fraction, and binary mass-ratio posterior distributions for each cluster. We perform a careful analysis of our completeness and also compare our results to previous spectroscopic surveys. For our sample of main-sequence stars with masses between 0.6 and 1 M ⊙, we find that these OCs have similar binary fractions that are also broadly consistent with the field multiplicity fraction. Within the clusters, the binary fraction increases dramatically toward the cluster centers, likely a result of mass segregation. Furthermore nearly all clusters show evidence of mass segregation within the single and binary populations. The OC binary fraction increases significantly with cluster age in our sample, possibly due to a combination of mass-segregation and cluster-dissolution processes. We also find a hint of an anticorrelation between binary fraction and cluster central density as well as total cluster mass, possibly due to an increasing frequency of higher-energy close stellar encounters that inhibit long-period binary survival and/or formation.

Exploring Be phenomena in OBA stars: A mid-infrared search

As early-type stars with a rotation speed close to their critical velocity, Be stars experience an event called the Be phenomenon. The material in their equator is ejected into outside space during the Be phenomenon and forms a circumstellar disk. The mechanism triggering these events remains poorly understood, and observations of these events are limited because the duration of these events ranges from months to years. Long-term epoch photometry in the infrared bands is expected to be ideal for detecting Be phenomena because the brightness variation is larger than that in the optical, and the effect of interstellar extinction is weaker as well. We conducted a systematic search for Be phenomena among Milky Way OBA stars in the mid-infrared. We examined the brightness and colour variations of known classical Be stars using the WISE W1 and W2 photometry bands to quantify their characteristics. Subsequently, we established a set of criteria to identify similar photometric variations in a large sample of OBA stars. We found 916 OBA stars that show Be phenomena in the past 13 yr, 736 of which are newly discovered. The peak-to-peak variations in magnitude and colour were found to be correlated, indicating that a decretion disk is common. The increase in colour was observed to be strongly correlated with the emission of the Hα line, providing further evidence of the association with circumstellar disks. The brightness variation of a star with Be phenomena can be up to 1.5 mag, and the colour variations can be up to 0.4 mag. The median durations for the disk build-up and decay phases are 474 and 524 days, respectively (durations shorter than 180 days are not sampled). The search for Be phenomena in the WISE bands greatly enlarges the number of stars showing disk variation, and it enables multi-band photometry analysis of these events with the help of current and future optical photometry surveys.

Abundance of strontium in the Galactic globular cluster 47 Tuc

Aims. We have determined Sr abundance in a sample of 31 red giant branch stars located in the Galactic globular cluster 47 Tuc with the aim to identify potential differences in the Sr abundance between first population (1P, Na-poor) and second population (2P, Na-rich) stars. Methods. We derived the Na and Sr abundances from the archival spectra obtained with the UVES spectrograph. To do this, we used 1D ATLAS9 model atmospheres and a 1D local thermodynamic equilibrium spectral synthesis method. Particular attention was paid to assessing the potential impact of CN line blending on the obtained Sr abundances. Furthermore, we evaluated the potential influence of convection on the Sr line formation by using 3D hydrodynamical model atmospheres computed with the CO5 BOLD code. Results. Our results suggest a weak correlation between the abundances of Sr and Na. Together with a similar correlation between the abundances of Zr and Na determined in our previous study, our analysis of Sr suggests that polluters that have enriched 2P stars with light elements may have produced some s-process elements as well. The mean Sr abundance determined in 31 red giant branch stars of 47 Tuc is ⟨[Sr/Fe]⟩ = 0.18 ± 0.08 (the error denotes the standard deviation due to the star-to-star abundance scatter). This value is within the range of the Sr abundance variation that is observed in Galactic field stars of similar metallicity. The mean [Sr/Zr] abundance ratio in our sample stars suggests that the two s-process elements could have been synthesized by either low-mass asymptotic giant branch stars (M = 1 − 4 M⊙) or massive (M = 10 − 20 M⊙) fast-rotating (vrot = 200 − 300 km s−1) stars.

Spectroscopic analysis of hot, massive stars in large spectroscopic surveys with de-idealized models

ABSTRACT Upcoming large-scale spectroscopic surveys with e.g. WEAVE (William herschel telescope Enhanced Area Velocity Explorer) and 4MOST (4-metre Multi-Object Spectroscopic Telescope) will provide thousands of spectra of massive stars, which need to be analysed in an efficient and homogeneous way. Usually, studies of massive stars are limited to samples of a few hundred objects, which pushes current spectroscopic analysis tools to their limits because visual inspection is necessary to verify the spectroscopic fit. Often uncertainties are only estimated rather than derived and prior information cannot be incorporated without a Bayesian approach. In addition, uncertainties of stellar atmospheres and radiative transfer codes are not considered as a result of simplified, inaccurate, or incomplete/missing physics or, in short, idealized physical models. Here, we address the question of ‘How to compare an idealized model of complex objects to real data?’ with an empirical Bayesian approach and maximum a posteriori approximations. We focus on application to large-scale optical spectroscopic studies of complex astrophysical objects like stars. More specifically, we test and verify our methodology on samples of OB stars in 30 Doradus region of the Large Magellanic Clouds using a grid of fastwind model atmospheres. Our spectroscopic model de-idealization analysis pipeline takes advantage of the statistics that large samples provide by determining the model error to account for the idealized stellar atmosphere models, which are included into the error budget. The pipeline performs well over a wide parameter space and derives robust stellar parameters with representative uncertainties.

Classification and parameterization of a large Gaia sample of white dwarfs using XP spectra

Context. The latest Gaia data release in July 2022, DR3, in addition to the refinement of the astrometric and photometric parameters from DR2, added a number of important data products to those available in earlier releases, including radial velocity data, information on stellar multiplicity, and XP spectra of a selected sample of stars. Gaia has proved to be an important search tool for white dwarf stars, which are readily identifiable from their absolute G magnitudes as low luminosity objects in the Hertzsprung–Russell (H–R) diagram. Each data release has yielded large catalogs of white dwarfs, containing several hundred thousand objects, far in excess of the numbers known from all previous surveys (∼40 000). While the normal Gaia photometry (G, GBP, and GRP bands) and astrometry can be used to identify white dwarfs with high confidence, it is much more difficult to parameterize the stars and determine the white dwarf spectral type from this information alone. Observing all stars in these catalogs with follow-up spectroscopy and photometry is also a huge logistical challenge with current facilities. Aims. The availability of the XP spectra and synthetic photometry presents an opportunity for a more detailed spectral classification and measurement of the effective temperature and surface gravity of Gaia white dwarfs. Methods. A magnitude limit of G < 17.6 was applied to the routine production of XP spectra for Gaia sources, which would have excluded most white dwarfs. Therefore, we created a catalog of 100 000 high-quality white dwarf identifications for which XP spectra were processed, with a magnitude limit of G < 20.5. Synthetic photometry was computed for all these stars, from the XP spectra, in Johnson, SDSS, and J-PAS, published as the Gaia Synthetic Photometry Catalog – White Dwarfs (GSPC-WD). We took this catalog and applied machine learning techniques to provide a classification of all the stars from the XP spectra. We have then applied an automated spectral fitting program, with χ-squared minimization, to measure their physical parameters (effective temperature and log g) from which we could estimate the white dwarf masses and radii. Results. We present the results of this work, demonstrating the power of being able to classify and parameterize such a large sample of ≈100 000 stars. We describe what we can learn about the white dwarf population from this dataset. We also explored the uncertainties in the process and the limitations of the dataset.