Search

Self-enrichment is one of the leading explanations for chemical anomalies in globular clusters. In this scenario, various candidate polluter stars have been proposed to eject gas with altered chemical composition during the self-enrichment process. Most of the proposed polluters will also eject radioactive |$^{26}$| Al into the surroundings. Hence, any detection of |$^{26}$| Al in young massive star clusters (YMCs) would support the self-enrichment scenario if YMCs were indeed the progenitors of globular clusters. Observations of gamma-ray data from COMPTEL and INTEGRAL, as well as detections of |$^{26}$| AlF molecules by the Atacama Large Millimeter-submillimeter Array (ALMA), indicate the maturing of |$^{26}$| Al detection methods. Detection possibilities will be enhanced in the short- to mid-term by the upcoming launch of the Compton Spectrometer and Imager (COSI). The Square Kilometre Array (SKA) could in principle also detect radio recombination lines of the positronium formed from the decay products of |$^{26}$| Al. Here, we show for a sample of YMCs in the nearby Universe, where self-enrichment could plausibly take place. For some nearby galaxies, this could enhance |$^{26}$| Al by an order of one magnitude. Detecting |$^{26}$| AlF with ALMA appears feasible for many candidate self-enrichment clusters, although significant challenges remain with other detection methods. The Large Magellanic Cloud, with its YMC R136, stands out as the most promising candidate. Detecting a 1.8 MeV radioactive decay line of |$^{26}$| Al here would require at least 15 months of targeted observation with COSI, assuming ongoing self-enrichment in R136. [ABSTRACT FROM AUTHOR]

We present time-series near-infrared spectra for the classical Cepheid, CP Cephei, from the Astrophysical Research Consortium 3.5-m telescope and near-infrared spectrograph, TripleSpec , at Apache Point Observatory, NM, USA. Spectral observations were made at nine points through the minimum and partway up the ascending portion of the optical light curve for the star. Carbon monoxide (CO) was detected in absorption in the 2.3- |$\mu$| m region for each observation. We measured the strength of CO absorption using the 2-0 band head in the feature for each observation and confirm that the CO varies with pulsation. We show that these measurements follow the |$(J-K)$| colour curve, confirming that temperature drives the destruction of CO. By obtaining convolved filter magnitudes from the spectral data we found that the effect of the CO feature on K magnitudes is small, unlike the CO feature in the mid-infrared at 4.5 |$\mu$| m. The dissociation of CO in the near-infrared spectra tracks with the effect seen in the mid-infrared photometric measurements of a similar Galactic Cepheid. Confirmation of the varying CO feature illustrates the need for further investigations into the related mid-infrared period–colour–metallicity relation in order to address the impact of Cepheid metallicities on the Hubble tension. [ABSTRACT FROM AUTHOR]

We study the contribution of various astrophysical events asymptotic giant branch (AGB stars, core collapse and thermonuclear supernovae, neutron star mergers, and collapsars) to the abundances of elements both up to and heavier than the iron peak in a Local Group dwarf irregular galaxy, Wolf–Lundmark–Melotte (WLM). Its star formation history has been recently determined by observations with the JWST , and we use it to estimate the occurrence of the astrophysical sources. The rates of the gas accretion and the outflow are roughly determined based on the stellar metallicity distribution, the oxygen abundance of H  ii regions, and the gas fraction. As discussed in the literature, the difference in time-scales on which the astrophysical events release the nucleosynthesis products is seen in the occurrence of the events and the evolution of abundance ratios. WLM has an extended star formation history and massive stars are recently and currently formed. Thus, the contribution of rotating massive stars through the weak s-process appears in the abundance ratios of light trans-iron elements to iron at later time of the evolution. [ABSTRACT FROM AUTHOR]

We present a detailed study of the chemical diversity of the metal-poor Milky Way using data from the GALAH DR3 survey. Considering 17 chemical abundances relative to iron ([X/Fe]) for 9923 stars, we employ principal component analysis (PCA) and extreme deconvolution (XD) to identify 10 distinct stellar groups. This approach, free from chemical or dynamical cuts, reveals known populations, including the accreted halo, thick disc, thin disc, and in situ halo. The thick disc is characterized by multiple substructures, suggesting it comprises stars formed in diverse environments. Our findings highlight the limited discriminatory power of magnesium in separating accreted and disc stars. Elements such as Ba, Al, Cu, and Sc are critical in distinguishing disc from accreted stars, while Ba, Y, Eu, and Zn differentiate disc and accreted stars from the in situ halo. This study demonstrates the potential power of combining a latent space representation of the data (PCA) with a clustering algorithm (XD) in Galactic archaeology, in providing new insights into the Galaxy's assembly and evolutionary history. [ABSTRACT FROM AUTHOR]

We present an artificial neural network (ANN) model of photospheric lithium depletion in cool stars (⁠|$3000\lt T_{\rm eff}/{\rm K} \lt 6500$|⁠), producing estimates and probability distributions of age from |$^7$| Li 6708 Å equivalent width (LiEW) and effective temperature data inputs. The model is trained on the same sample of 6200 stars from 52 open clusters, observed in the Gaia -ESO spectroscopic survey, and used to calibrate the previously published analytical eagles model, with ages 2–6000 Myr and |$-0.3 \lt $| [Fe/H] |$\lt 0.2$|⁠. The additional flexibility of the ANN provides some improvements, including better modelling of the 'lithium dip' at ages |$\lt 50$|  Myr and |$T_{\rm eff}\sim 3500$|  K, and of the intrinsic dispersion in LiEW at all ages. Poor age discrimination is still an issue at ages >1 Gyr, confirming that additional modelling flexibility is not sufficient to fully represent the LiEW–age–T |$_{\text{eff}}$| relationship, and suggesting the involvement of further astrophysical parameters. Expansion to include such parameters–rotation, accretion, and surface gravity–is discussed, and the use of an ANN means these can be more easily included in future iterations, alongside more flexible functional forms for the LiEW dispersion. Our methods and ANN model are provided in an updated version 2.0 of the eagles software. [ABSTRACT FROM AUTHOR]

Hydrogen-deficient carbon (HdC) stars are rare, low-mass, chemically peculiar, supergiant variables believed to be formed by a double white dwarf (DWD) merger, specifically of a carbon/oxygen- (CO-) and a helium-white dwarf (He-WD). They consist of two subclasses – the dust-producing R Coronae Borealis (RCB) variables and their dustless counterparts the dustless HdCs (dLHdCs). Additionally, there is another, slightly cooler set of potentially related carbon stars, the DY Persei type variables which have some, but not conclusive, evidence of hydrogen-deficiency. Recent works have begun to explore the relationship between these three classes of stars, theorizing that they share an evolutionary pathway (a DWD merger) but come from different binary populations, specifically different total masses (⁠|$M_\text{tot}$|⁠) and mass ratios (q). In this work, we use the mesa modelling framework that has previously been used to model RCB stars and vary the merger parameters, |$M_\text{tot}$| and q , to explore how those parameters affect the abundances, temperatures, and luminosities of the resultant post-merger stars. We find that lower |$M_\text{tot}$| and larger q 's both decrease the luminosity and temperatures of post-merger models to the region of the Hertzsprung–Russell diagram populated by the dLHdCs. These lower |$M_\text{tot}$| and larger q models also have smaller oxygen isotopic ratios (⁠|$^{16}$| O/ |$^{18}$| O) which is consistent with recent observations of dLHdCs compared to RCBs. None of the models generated in this work can explain the existence of the DY Persei type variables, however this may arise from the assumed metallicity of the models. [ABSTRACT FROM AUTHOR]

We study metal enrichment originating from stellar wind and supernovae in low-metallicity clouds by performing three-dimensional radiation hydrodynamics simulations. We find that metals ejected from stellar wind are accumulated, leading to subsequent star formation in the nitrogen-enriched gas. During this early phase, the |${\rm N/O}$| ratios are similar to observed nitrogen-enriched galaxies (⁠|${\rm [N/O]}\gtrsim 0.5$|⁠). Then, once supernovae occur, the |${\rm N/O}$| ratios decrease significantly. If the duration of star formation is comparable to the time-scale of supernovae, the mass fraction of nitrogen-enriched stars reaches half the mass of star clusters. We suggest that the mass of the star cluster needs to exceed |$\sim \!10^6$|   M |$_{\odot }$| to have multiple populations due to stellar wind, considering the condition for massive star cluster formation and the timescales of stellar evolution. [ABSTRACT FROM AUTHOR]

Under the assumption of hierarchical galaxy formation, dwarf galaxies are the closest existing analogues to the high-redshift protogalaxies that merged to form the Milky Way. These low-mass systems serve as unique laboratories for studying nucleosynthetic channels given that the chemical compositions of their stars play a pivotal role in constraining their chemical enrichment history. To date, stellar abundances in dwarf galaxies have focused almost exclusively on elemental abundance ratios. While important, elemental abundances omit critical information about the isotopic composition. Here, we compute the Mg isotopic ratios of six accreted dwarf galaxy stars (low |$\alpha$|⁠) and seven Milky Way stars (high |$\alpha$|⁠) using a set of high-resolution (65 000 < R < 160 000) and high signal-to-noise ratio (⁠|$\rm {S/N} \gt 250$|⁠) optical spectra. We show, for the first time, that at a given [Fe/H] stars born in a dwarf galaxy differ in their Mg isotopic ratios from stars born in the Milky Way. However, when comparing isotopic ratios at a given [Mg/H] rather than [Fe/H], a powerful diagnostic emerges that suggests nucleosynthesis processes are consistent across different stellar environments. This universality of Mg isotopic abundances provides additional dimensionality for chemical evolution models and helps to constrain massive star nucleosynthesis across cosmic time. [ABSTRACT FROM AUTHOR]

At metallicities lower than that of the Small Magellanic Cloud, it remains essentially unexplored how fossil magnetic fields, forming large-scale magnetospheres, could affect the evolution of massive stars, thereby impacting the fundamental building blocks of the early Universe. We extend our stellar evolution model grid with representative calculations of main-sequence, single-star models with initial masses of 20 and 60 M |$_\odot$|⁠ , including appropriate changes for low-metallicity environments (⁠|$Z = 10^{-3}$| – |$10^{-6}$|⁠). We scrutinize the magnetic, rotational, and chemical properties of the models. When lowering the metallicity, the rotational velocities can become higher and the tendency towards quasi-chemically homogeneous evolution increases. While magnetic fields aim to prevent the development of this evolutionary channel, the weakening stellar winds lead to less efficient magnetic braking in our models. Since the stellar radius is almost constant during a blueward evolution caused by efficient chemical mixing, the surface magnetic field strength remains unchanged in some models. We find core masses at the terminal-age main sequence between 22 and 52 M |$_\odot$| for initially 60 M |$_\odot$| models. This large difference is due to the vastly different chemical and rotational evolution. We conclude that in order to explain chemical species and, in particular, high nitrogen abundances in the early Universe, the adopted stellar models need to be under scrutiny. The assumptions regarding wind physics, chemical mixing, and magnetic fields will strongly impact the model predictions. [ABSTRACT FROM AUTHOR]

Context. Recent evidence from spectroscopic surveys points towards the presence of a metal-poor, young stellar population in the low- α, chemically thin disk. In this context, the investigation of the spatial distribution and time evolution of precise, unbiased abundances is fundamental to disentangle the scenarios of formation and evolution of the Galaxy. Aims. We study the evolution of abundance gradients in the Milky Way by taking advantage of a large sample of open star clusters, which are among the best tracers for this purpose. In particular, we used data from the last release of the Gaia-ESO survey. Methods. We performed a careful selection of open cluster member stars, excluding those members that may be affected by biases in spectral analysis. We compared the cleaned open cluster sample with detailed chemical evolution models for the Milky Way, using well-tested stellar yields and prescription for radial migration. We tested different scenarios of Galaxy evolution to explain the data, namely, the two-infall and the three-infall frameworks, which suggest the chemical thin disk is formed by one or two subsequent gas accretion episodes, respectively. Results. With the performed selection in cluster member stars, we still find a metallicity decrease between intermediate-age (1 < Age/Gyr < 3) and young (Age < 1 Gyr) open clusters. This decrease cannot be explained in the context of the two-infall scenario, even by accounting for the effect of migration and yield prescriptions. The three-infall framework, with its late gas accretion in the last 3 Gyr, is able to explain the low metallic content in young clusters. However, we have invoked a milder metal dilution for this gas infall episode relative to previous findings. Conclusions. To explain the observed low metallic content in young clusters, we propose that a late gas accretion episode triggering a metal dilution would have taken place, extending the framework of the three-infall model for the first time to the entire Galactic disk. [ABSTRACT FROM AUTHOR]

Context. The atmospheres of phosphorus-rich (P-rich) stars have been shown to contain between 10 and 100 times more P than our Sun. Given its crucial role as an essential element for life, it is especially necessary to uncover the origin of P-rich stars to gain insights into the still unknown nucleosynthetic formation pathways of P in our Galaxy. Aims. Our objective is to obtain the extensive chemical abundance inventory of four P-rich stars, covering a large range of heavy (Z > 30) elements. This characterization will serve as a milestone for the nuclear astrophysics community to uncover the processes that form the unique chemical fingerprint of P-rich stars. Methods. We performed a detailed 1D local thermodynamic equilibrium abundance analysis on the optical UVES spectra of four P-rich stars. The abundance measurements, complemented with upper-limit estimates, included 48 light and heavy elements. Our focus lay on the neutron-capture elements (Z > 30), in particular, on the elements between Sr and Ba, as well as on Pb, as they provide valuable constraints to nucleosynthesis calculations. In past works, we showed that the heavy-element observations from the first P-rich stars are not compatible with either classical s-process or r-process abundance patterns. In this work, we compare the obtained abundances with three different nucleosynthetic scenarios: a single i-process, a double i-process, and a combination of s- and i-processes. Results. We have performed the most extensive abundance analysis of P-rich stars to date, including the elements between Sr and Ba, such as Ag, which are rarely measured in any type of stars. We also estimated constraining upper limits for Cd I, In I, and Sn I. We found overabundances with respect to solar in the s-process peak elements, accompanied by an extremely high Ba abundance and slight enhancements in some elements between Rb and Sn. No global solution explaining all four stars could be found for the nucleosynthetic origin of the pattern. The model that produces the least number of discrepancies in three of the four stars is a combination of s- and i-processes, but the current lack of extensive multidimensional hydrodynamic simulations to follow the occurrence of the i-process in different types of stars makes this scenario highly uncertain. [ABSTRACT FROM AUTHOR]

This work aims to analyze some of the polluters proposed in the self-enrichment scenarios put forward to explain the multiple populations in globular clusters (GCs), extending previous studies. Three scenarios with different polluter stars were tested: asymptotic giant branch stars (AGBs), high-mass interacting binaries (IBs), and fast rotating massive stars (FRMSs). With abundance data available from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey and ΔY estimates from precise Hubble Space Telescope (HST) photometry, twenty-six clusters were studied, increasing the number of clusters in previous studies by more than a factor of three. We also included the study of the abundances of N, C, Mg, and Al, extending previous studies that mainly focused on the abundances of He, O, and Na. In addition, we constructed an empirical model to test whether one could explain the chemical signatures of the "enriched" population of GC stars with a fixed source and dilution process based on empirical data. In agreement with work by other authors, we found that the proposed polluters can generally predict the qualitative abundance patterns in GC stars and in some cases quantitatively predict some elements, but in most cases when we compare the model yields with the observations, we find that they cannot explain the entire set of observed abundance patterns. The empirical model succeeds in reproducing the abundances of Al for a given ΔY (and vice versa), showing that there is a direct relationship between Al and He, with one increasing proportionally to the other. However, the empirical model fails to reproduce the observed abundances of Na and N, in agreement with the results of previous works. The observed decoupling between the maximum abundances of CNO-cycle elements such as N and Na with those of Al and He provides new information and constraints for future models and could take us a step closer to understanding the origin of the peculiar abundance variations of GC stars. [ABSTRACT FROM AUTHOR]

We aim to constrain the chemo-dynamical properties of the Sagittarius (Sgr) dwarf galaxy using carbon abundances. At low metal- licities in particular, these properties reveal the early chemical evolution of a system, tracing the contributing supernovae (SNe) and how much of their ejecta eventually made it into the next stellar generation. Our sample from the Pristine Inner Galaxy Survey (PIGS) includes ~350 metal-poor ([Fe/H] < −1.5) stars in the main body of Sgr with good quality spectroscopic observations. Our metal-poor Sgr population has a larger velocity dispersion than metal-rich Sgr from the literature, which could be explained by outside-in star formation, extreme Galactic tidal perturbations, and/or the presence of a metal-rich disc and bar + metal-poor halo. The average carbon abundance [C/Fe] in Sgr is similar to that of other classical dwarf galaxies (DGs) and consistently lower than in the Milky Way by ~0.2–0.3 dex at low metallicities. The interstellar medium in DGs, including Sgr, may have retained yields from more energetic Population III and II supernovae (SNe), thereby reducing the average [C/Fe]. Additionally, SNe Ia producing more Fe than C would start to contribute at lower metallicity in DGs/Sgr than in the Galaxy. The presence of a [C/Fe] gradient for Sgr stars with [Fe/H] ≳ −2.0 (~6.8 × 10−4 dex arcmin−1) suggests that SNe la contributed to the system at those metallicities, especially in its inner regions. There is a low frequency of carbon-enhanced metal-poor (CEMP) stars in our Sgr sample. At higher metallicities and carbon abundances (i.e. mostly CEMPs), this may be due to photometric selection effects, but those are less likely to affect non-CEMP stars. Given the lower average [C/Fe] in DGs, we propose using the same CEMP definition ([C/Fe] > +0.7) as that applied to the Galaxy at large ends up underpredicting the number of CEMP stars in DGs. Burthermore, for Sgr, a cut at [C/Fe] ∽ +0.35 may be more appropriate, which brings the frequency of CEMP stars in agreement with that of the whole Galaxy. [ABSTRACT FROM AUTHOR]

Context. Neutron-capture elements represent an important nucleosynthetic channel in the study of the Galactic chemical evolution of stellar populations. For stellar populations behind significant extinction, such as those in the Galactic centre and along the Galactic plane, abundance analyses based on near-infrared (NIR) spectra are necessary. Previously, spectral lines from the neutron-capture elements, such as copper (Cu), cerium (Ce), neodymium (Nd), and ytterbium (Yb), have been identified in the H band, while yttrium (Y) lines have been identified in the K band. Aims. Due to the scarcity of spectral lines from neutron-capture elements in the NIR, the addition of useful spectral lines from other neutron-capture elements is highly desirable. The aim of this work is to identify and characterise a spectral line suitable for abundance determination from the most commonly used s-process element, namely barium. Methods. We observed the NIR spectra of 37 M giants in the solar neighbourhood at high spectral resolution and with a high signal-to-noise ratio using the IGRINS spectrometer on the GEMINI South telescope. The full H- and K-bands were recorded simultaneously at R = 45 000. Using a manual spectral synthesis method, we determined the fundamental stellar parameters for these stars and derived the barium abundance from the Ba line (6s5d 3D2 → 6s6p 3P2o) at λair = 23 253.56 Å in the K band. Results. We demonstrate that the Ba line in the K band at 2.33 μm (λ23 253.56) is useful for abundance analyses from the spectra of M giants. The line becomes progressively weaker at higher temperatures and is only useful in M giants and the coolest K giants at supersolar metallicities. Conclusions. We can now add Ba to the trends of the heavy elements Cu, Zn, Y, Ce, Nd, and Yb, which can be retrieved from high-resolution H- and K-band spectra. This opens up the study of nucleosynthetic channels, including the s-process and the r-process, in dust-obscured populations. Thus, these elements can be studied for heavily dust-obscured regions of the Galaxy, such as the Galactic centre. [ABSTRACT FROM AUTHOR]

We present a high-resolution chemical study of a representative sample of 21 luminous giant stars in Liller 1, a complex stellar system in the Galactic bulge, based on H-band spectra acquired with the Near-Infrared Spectrograph at KeckII. In this sample, we found fifteen stars with a subsolar iron abundance and enhanced [α/Fe] and [Al/Fe], likely older, having formed early and quickly from gas mainly enriched by type II supernovae, and six stars with supersolar iron and roughly solar-scaled [α/Fe] and [Al/Fe], likely younger, having formed at later epochs from gas also enriched by type Ia supernovae. Moreover, both subpopulations show enhanced [N/Fe], as in the bulge field, approximately solar-scaled [V/Fe], and depletion of [C/Fe] and 12C/13C with respect to the solar values, indicating the occurrence of significant mixing in the stellar interiors of these evolved stars. Our study also reveals that the subsolar subpopulation shows some structuring, and the presence of a third subcomponent with iron content and intermediate [α/Fe] enhancement, in between that of the metal-poor and metal-rich main subpopulations, has been statistically assessed, providing the chemical signature of both an extended star formation with multiple bursts and some self-enrichment. [ABSTRACT FROM AUTHOR]

Context. Dwarf galaxy streams encode vast amounts of information essential to understanding early galaxy formation and nucleosynthesis channels. Due to the variation in the timescales of star formation history in their progenitors, stellar streams serve as 'snapshots' that record different stages of galactic chemical evolution. Aims. This study focusses on the Cetus stream, stripped from a low-mass dwarf galaxy. We aim to uncover its chemical evolution history as well as the different channels of its element production from detailed elemental abundances. Methods. We carried out a comprehensive analysis of the chemical composition of 22 member stars based on their high-resolution spectra. We derived abundances for up to 28 chemical species from C to Dy and, for 20 of them, we account for the departures from local thermodynamic equilibrium (NLTE effects). Results. We confirm that the Cetus stream has a mean metallicity of [Fe/H] = −2.11 ± 0.21. All observed Cetus stars are α enhanced with [α/Fe] ≃ 0.3. The absence of the α-'knee' implies that star formation stopped before iron production in type Ia supernovae (SNe Ia) became substantial. Neutron capture element abundances suggest that both the rapid (r-) and the main slow (s-) processes contributed to their origin. The decrease in [Eu/Ba] from a typical r-process value of [Eu/Ba] = 0.7–0.3 with increasing [Ba/H] indicates a distinct contribution of the r- and s-processes to the chemical composition of different Cetus stars. For barium, the r-process contribution varies from 100 to 20% in different sample stars, with an average value of 50%. Conclusions. Our abundance analysis indicates that the star formation in the Cetus progenitor ceased after the onset of the main s-process in low- to intermediate-mass asymptotic giant branch stars but before SNe Ia played an important role. A distinct evolution scenario is revealed by comparing the abundances in the Ursa Minor dwarf spheroidal galaxy, showing the diversity in – and uniqueness of – the chemical evolution of low-mass dwarf galaxies. [ABSTRACT FROM AUTHOR]

Context. In stars, metallicity is usually traced using Fe, while in nebulae, O serves as the preferred proxy. Both elements have different nucleosynthetic origins and are not directly comparable. Additionally, in ionized nebulae, Fe is heavily depleted onto dust grains. Aims. We investigate the distribution of Fe gas abundances in a sample of 452 star-forming nebulae with [Fe III] λ4658 detections and their relationship with O and N abundances. Additionally, we analyze the depletion of Fe onto dust grains in photoionized environments. Methods. We homogeneously determined the chemical abundances with direct determinations of electron temperature (Te), considering the effect of possible internal variations of this parameter. We adopted a sample of 300 Galactic stars to interpret the nebular findings. Results. We find a moderate linear correlation (r = −0.59) between Fe/O and O/H. In turn, we report a stronger correlation (r = −0.80) between Fe/N and N/H. We interpret the tighter correlation as evidence that Fe and N are produced on similar timescales while Fe- dust depletion scales with the Fe availability. The apparently flat distribution between Fe/N and N/H in Milky Way stars supports this interpretation. We find that when 12+log(O/H)<7.6, the nebulae seem to reach a plateau value around log(Fe/O) ≈ −1.7. If this trend were confirmed, it would be consistent with a very small amount of Fe dust in these systems, similar to what is observed in high-z galaxies discovered by the James Webb Space Telescope (JWST). We derive a relationship that allows us to approximate the fraction of Fe trapped into dust in ionized nebulae. If the O-dust scales in the same way, its possible contribution in low-metallicity nebulae would be negligible. After analyzing the Fe/O abundances in J0811+4730 and J1631+4426, we do not see evidence of the presence of very massive stars with Minit > 300 M⊙ in these systems. Conclusions. The close relation observed between the N and Fe abundances has the potential to serve as a link between stellar and nebular chemical studies. This requires an expansion of the number of abundance determinations for these elements in both stars and star-forming nebulae, especially at low metallicities. [ABSTRACT FROM AUTHOR]

Context. The evolution and fate of massive stars are thought to be affected by rotationally induced internal mixing. The surface boron abundance is a sensitive tracer of this in early B-type main sequence stars. Aims. We test current stellar evolution models of massive main sequence stars which include rotational mixing through a systematic study of their predicted surface boron depletion. Methods. We construct a dense grid of rotating single star models using MESA, for which we employ a new nuclear network which follows all the stable isotopes up to silicon, including lithium, beryllium, boron, as well as the radioactive isotope aluminium-26. We also compile the measured physical parameters of the 90 Galactic early B-type stars with boron abundance information. We then compare each observed stars with our models through a Bayesian analysis, which yields the mixing efficiency parameter with which the star is reproduced the best, and the probability that it is represented by the stellar models. Results. We find that about two-thirds of the sample stars are well represented by the stellar models, with the best agreement achieved for a rotational mixing efficiency of ∼50% compared to the widely adopted value. The remaining one third of the stars, of which many are strongly boron depleted slow rotators, are largely incompatible with our models, for any rotational mixing efficiency. We investigate the observational incidence of binary companions and surface magnetic fields, and discuss their evolutionary implications. Conclusions. Our results confirm the concept of rotational mixing in radiative stellar envelopes. On the other hand, we find that a different boron depletion mechanism, and likely a different formation path, is required to explain about one-third of the sample stars. The large spread in the surface boron abundances of these stars may hold a clue to understanding their origin. [ABSTRACT FROM AUTHOR]

Context. The chemical evolution of neutron capture elements in the Milky Way is still a matter of debate. Although more and more studies investigate their chemical behaviour, there is still a lack of a significant large sample of abundances of a key heavy element: lead. Aims. Lead is the final product of the s-process nucleosynthesis channel and is one of the most stable heavy elements. The goal of this article is to present the largest catalogue of homogeneous Pb abundances, in particular for metallicities higher than −1.0 dex, and then to study the lead content of the Milky Way. Methods. We analysed high-resolution spectra from the ESO UVES and FEROS archives. Atmospheric parameters were taken from the AMBRE parametrisation. We used the automated abundance method GAUGUIN to derive lead abundances in 653 slow-rotating FGK-type stars from the 368.34 nm Pb I line. Results. We present the largest catalogue of Local Thermodynamic Equilibrium (LTE) and non-LTE lead abundances ever published with metallicities ranging from −2.9 to 0.6 dex and [Pb/Fe] from −0.7 to 3.3 dex. Within this sample, no lead-enhanced Asymptotic Giant Branch (AGB) stars were found, but nine lead-enhanced metal-poor stars ([Pb/Fe] > 1.5) were detected. Most of them were already identified as carbon-enhanced metal-poor stars with enrichments in other s-process species. The lead abundance of 13 Gaia Benchmark Stars are also provided. We then investigated the Pb content of the Milky Way disc by computing vertical and radial gradients and found a slightly decreasing [Pb/Fe] radial trend with metallicity. This trend together with other related ratios ([Pb/Eu], [Pb/Ba], and [Pb/α]) are interpreted thanks to chemical evolution models. The two-infall model closely reproduces the observed trends with respect to the metallicity. It is also found that the AGB contribution to the Pb Galactic enrichment has to be strongly reduced. Moreover, the contribution of massive stars with rather high rotational velocities should be favoured in the low-metallicity regime. [ABSTRACT FROM AUTHOR]

Context. The study of exoplanets at different evolutionary stages can shed light on their formation, migration, and evolution. The determination of exoplanet properties depends on the properties of their host stars. It is therefore important to characterise the host stars for accurate knowledge on their planets. Aims. Our final goal is to derive, in a homogeneous and accurate way, the stellar atmospheric parameters and elemental abundances of ten young TESS (Transiting Exoplanet Survey Satellite) transiting planet-hosting GK stars followed up with the HARPS-N (High Accuracy Radial velocity Planet Searcher for the Northern hemisphere) at TNG (Telescopio Nazionale Galileo) spectrograph within the Global Architecture of Planetary Systems (GAPS) programme. Methods. We derived stellar kinematic properties, atmospheric parameters, and abundances of 18 elements. Depending on stellar parameters and chemical elements, we used methods based on line equivalent widths and spectral synthesis. Lithium line measurements were used as approximate age estimations. We exploited chemical abundances and their ratios to derive information on planetary composition. Results. Elemental abundances and kinematic properties are consistent with the nearby Galactic thin disk. All targets show C/O<0.8 and 1.0

The Milky Way is a mosaic of stars from different origins. In particular, metal-poor accreted star candidates offer a unique opportunity to better understand the accretion history of the Milky Way. In this work, we aim to explore the assembly history of the Milky Way by investigating accreted stars in terms of their ages, dynamical properties, and chemical abundances. We also aim to better characterize the impact of incorporating asteroseismic information on age and chemical abundance calculations of metal-poor accreted stars for which TESS data are available. In this study, we conducted an in-depth examination of 30 metal-poor accreted star candidates using TESS and Gaia data as well as MIKE spectra. We find satisfactory agreement between seismic surface gravity (log ɡ) values and values obtained using spectroscopy, demonstrating the reliability of spectroscopic data produced by our methodology. We find that while age determination is highly dependent on the log g and asteroseismic information used, the overall chemical abundance distributions are similar for different log ɡ. However, we find that calcium (Ca) abundances are more sensitive to the adopted log ɡ. Our study reveals that the majority of our stars have properties that are compatible with those reported for the Gai'a-Sausage-Enceladus, with a minority of stars that might be associated with Splash. We find an age distribution with a median of 11.3−4.1+1.3 Gyr when including asteroseismic information. Regarding some key chemical signatures, we note that these stars are metal poor ([Fe/H]) < −0.8), α rich ([α]/Fe] > 0.2), and copper poor ([Cu/Fe] < 0), with chemical abundances typical of accreted stars. These findings illustrate the importance of multidimensional analyses in unraveling the complex accretion history of the Milky Way. [ABSTRACT FROM AUTHOR]

Deep imaging of galaxy cluster fields have in recent years revealed tens of candidates for gravitationally lensed stars at redshifts z ≈ 1 − 6, and future searches are expected to reveal highly magnified stars from even earlier epochs. Multi-band photometric observations may be used to constrain the redshift, effective temperature Teff, and dust attenuation along the line of sight to such objects. When combined with an estimate of the likely magnification, these quantities may be converted into a constraint on the stellar luminosity and, for an adopted set of stellar evolutionary tracks, the initial stellar mass. Further characterisation is difficult, however, without spectroscopic observations, which at the typical brightness levels of high-redshift lensed stars becomes extremely challenging for even the largest existing telescopes. Here, we explore what spectral features one can realistically hope to detect in lensed stars with peak brightness in the range 26–28 AB mag, Teff = 4000 − 50 000 K, and redshifts z = 1 − 10, using spectroscopy with JWST and the forthcoming ELT. We find that a majority of detectable lines appear in the rest-UV range for stars with Teff ≥ 15 000 K. The strongest detectable spectral lines are the C IVλ1550 Å line and the Si IVλλ1393, 1403 Å-doublet at Teff = 30 000 K. For lower temperatures, the calcium H- and K-lines at Teff = 6000 K are among the most readily detectable. In limited wavelength ranges, ELT is expected to provide more sensitive spectroscopic observations, and with higher resolution than JWST. We find that variations in both mass-loss rate and metallicity lead to noticeable effects in the detectability of certain spectral lines with both JWST and ELT. [ABSTRACT FROM AUTHOR]

Multiple populations (MPs) in globular clusters (GCs) are stars that are distinct for their abundances of light elements. The MPs can be directly separated by measuring abundances of C, N, O, Na, Al, and Mg with spectroscopy or indirectly from photometric sequences created by the impact of different chemistry on band passes of particular filters, such as the HST pseudo-colours in the ultraviolet. An attempt to link HST pseudo-colour maps (PCMs) and spectroscopy was made by Marino et al. (2019, MNRAS, 487, 3815), using abundances mostly from our FLAMES survey. However, we found that an incomplete census of stars in common was used in their population tagging. We corrected the situation by building our own PCMs and matching them with our abundances in 20 GCs, plus two GCs from other sources, doubling the sample with spectroscopic abundances available. We found that the pseudo-colour (magF275W − 2 × magF336W + magF438) does not have a monotonic trend with Na abundances, enhanced by proton-capture reactions in MPs. Moreover, on average about 16% of stars with spectroscopic Na abundances show a discrepant tagging of MPs with respect to the HST photometry. Stars with second generation (SG) chemistry are mistaken for first generation (FG) objects according to HST photometry and vice versa. In general, photometric indices tend to overestimate the fraction of FG stars, in particular in low mass GCs. We offer a simple explanation for these findings. Finally, we publish all our PCMs (with more than 31 800 stars in 22 GCs) with star ID and coordinates; this is done to ensure easy verification and reproduction, as should be the case in scientific papers. [ABSTRACT FROM AUTHOR]

Context. Classical Cepheids (DCEPs) are crucial for calibrating the extragalactic distance ladder, ultimately enabling the determination of the Hubble constant through the period-luminosity (PL) and period-Wesenheit (PW) relations that they exhibit. Hence, it is vital to understand how the PL and PW relations depend on metallicity. This is the purpose of the C-MetaLL survey, within which this work is situated. The DCEPs are also very important tracers of the young populations placed along the Galactic disc. Aims. We aim to enlarge the sample of DCEPs with accurate abundances from high-resolution spectroscopy. In particular, our goal is to extend the range of measured metallicities towards the metal-poor regime to better cover the parameter space. To this end, we observed objects in a wide range of Galactocentric radii, allowing us to study in detail the abundance gradients present in the Galactic disc. Methods. We present the results of the analysis of 331 spectra obtained for 180 individual DCEPs with a variety of high-resolution spectrographs. For each target, we derived accurate atmospheric parameters, radial velocities, and abundances for up to 29 different species. The iron abundances range between 0.5 and −1 dex with a rather homogeneous distribution in metallicity. Results. The sample presented in this paper was complemented with that already published in the context of the C-MetaLL survey, resulting in a total of 292 pulsators whose spectra have been analysed in a homogeneous way. These data were used to study the abundance gradients of the Galactic disc in a range of Galactocentric radii (RGC) spanning the range of 5–20 kpc. Conclusions. For most of the elements, we have found a clear negative gradient, with a slope of −0.064 ± 0.003 dex kpc−1 for [Fe/H] case. Through a qualitative fit with the Galactic spiral arms, we show how our farthest targets (RGC > 10 kpc) trace both the Outer and Outer Scutum-Centaurus arms. The homogeneity of the sample will be of pivotal importance for the study of the metallicity dependence of the DCEP PL relations. [ABSTRACT FROM AUTHOR]

Context. The third data release of Gaia, has provided stellar parameters, metallicity [M/H], [α/Fe], individual abundances, broadening parameter from its Radial Velocity Spectrograph (RVS) spectra for about 5.6 million objects thanks to the GSP-Spec module, implemented in the Gaia pipeline. The catalogue also publishes the radial velocity of 33 million sources. In recent years, many spectroscopic surveys with ground-based telescopes have been undertaken, including the public survey Gaia-ESO, designed to be complementary to Gaia, in particular towards faint stars. Aims. We took advantage of the intersections between Gaia RVS and Gaia-ESO to compare their stellar parameters, abundances and radial and rotational velocities. We aimed at verifying the overall agreement between the two datasets, considering the various calibrations and the quality-control flag system suggested for the Gaia GSP-Spec parameters. Methods. For the targets in common between Gaia RVS and Gaia-ESO, we performed several statistical checks on the distributions of their stellar parameters, abundances and velocities of targets in common. For the Gaia surface gravity and metallicity we considered both the uncalibrated and calibrated values. Results. Overall, there is a good agreement between the results of the two surveys. We find an excellent agreement between the Gaia and Gaia-ESO radial velocities given the uncertainties affecting each dataset. Less than 25 out of the ≈2100 Gaia-ESO spectroscopic binaries are flagged as non-single stars by Gaia. For the effective temperature and in the bright regime (G ≤ 11), we found a very good agreement, with an absolute residual difference of about 5 K (±90 K) for the giant stars and of about 17 K (±135 K) for the dwarf stars; in the faint regime (G ≥ 11), we found a worse agreement, with an absolute residual difference of about 107 K (±145 K) for the giant stars and of about 103 K (±258 K) for the dwarf stars. For the surface gravity, the comparison indicates that the calibrated gravity should be preferred to the uncalibrated one. For the metallicity, we observe in both the uncalibrated and calibrated cases a slight trend whereby Gaia overestimates it at low metallicity; for [M/H] and [α/Fe], a marginally better agreement is found using the calibrated Gaia results; finally for the individual abundances (Mg, Si, Ca, Ti, S, Cr, Ni, Ce) our comparison suggests to avoid results with flags indicating low quality (XUncer = 2 or higher). These remarks are in line with the ones formulated by GSP-Spec. We confirm that the Gaia vbroad parameter is loosely correlated with the Gaia-ESO v sin i for slow rotators. Finally, we note that the quality (accuracy, precision) of the GSP-Spec parameters degrades quickly for objects fainter than G ≈ 11 or GRVS ≈ 10. Conclusions. We find that the somewhat imprecise GSP-Spec abundances due to its medium-resolution spectroscopy over a short wavelength window and the faint G regime of the sample under study can be counterbalanced by working with averaged quantities. We extended our comparison to star clusters using averaged abundances, using not only the stars in common, but also the members of clusters in common between the two samples, still finding a very good agreement. Encouraged by this result, we studied some properties of the open-cluster population, using both Gaia-ESO and Gaia clusters: our combined sample traces very well the radial metallicity and [Fe/H] gradients, the age-metallicity relations in different radial regions, and allows us to place the clusters in the thin disc. [ABSTRACT FROM AUTHOR]

Context. In modern Galactic astronomy, stellar spectroscopy plays a pivotal role in complementing large photometric and astrometric surveys and enabling deeper insights to be gained into the chemical evolution and chemo-dynamical mechanisms at play in the Milky Way and its satellites. Nonetheless, the use of different instruments and dedicated pipelines in various spectroscopic surveys can lead to differences in the derived spectroscopic parameters. Aims. Efforts to homogenise these surveys onto a common scale are essential to maximising their scientific legacy. To this aim, we developed the SPECTROTRANSLATOR, a data-driven deep neural network algorithm that converts spectroscopic parameters from the base of one survey (base A) to that of another (base B). Methods. SPECTROTRANSLATOR is comprised of two neural networks: an intrinsic network, where all the parameters play a role in computing the transformation, and an extrinsic network, where the outcome for one of the parameters depends on all the others, but not the reverse. The algorithm also includes a method to estimate the importance that the various parameters play in the conversion from base A to B. Results. To demonstrate the workings of the algorithm, we applied it to transform effective temperature, surface gravity, metallicity, [Mg/Fe], and line-of-sight velocity from the base of GALAH DR3 into the APOGEE-2 DR 17 base. We demonstrate the efficiency of the SPECTROTRANSLATOR algorithm to translate the spectroscopic parameters from one base to another, directly using parameters by the survey teams. We were able to achieve a similar performance than previous works that have performed a similar type of conversion but using the full spectrum, rather than the spectroscopic parameters. This allowed us to reduce the computational time and use the output of pipelines optimised for each survey. By combining the transformed GALAH catalogue with the APOGEE-2 catalogue, we studied the distribution of [Fe/H] and [Mg/Fe] across the Galaxy and we found that the median distribution of both quantities present a vertical asymmetry at large radii. We attribute it to the recent perturbations generated by the passage of a dwarf galaxy across the disc or by the infall of the Large Magellanic Cloud. Conclusions. Several aspects still need to be refined, such as the question of the optimal way to deal with regions of the parameter space meagrely populated by stars in the training sample. However, SPECTROTRANSLATOR has already demonstrated its capability and is poised to play a crucial role in standardising various spectroscopic surveys onto a unified framework. [ABSTRACT FROM AUTHOR]

Context. The discrepancy between the predictions of Big Bang nucleosynthesis and the lithium abundance observed in the oldest stars of our Galaxy, known as the cosmological lithium problem, has long been regarded as a challenge to the fields of both cosmology and astrophysics. Aims. In light of recent theoretical advances concerning the transport of chemicals and angular momentum in Population I low-mass stars, we re-examine the stellar depletion hypothesis to explain the lithium plateau, which spans a wide range of metallicities over a specific range of stellar effective temperature. Methods. We computed stellar evolution models with the code STAREVOL, including the same input physics that enable self-consistent reproduction of the Li depletion in the Sun and stars in open clusters, while accounting for internal rotation consistent with asteroseismic constraints. In addition to atomic diffusion and parametric turbulence, which were considered in previous studies of Li depletion along the plateau, our models include rotation-induced hydrodynamical processes and additional parametric viscosity for the transport of angular momentum as well as penetrative convection with a rotational dependence, and magnetic braking. Results. As in the case of Pop I stars, the mixing obtained with the current prescriptions for vertical and horizontal shear turbulence induced by rotation is insufficient to reproduce the Li constraints, and parametric turbulence is required. Even if the nature of the turbulence has yet to be identified, we show that the compactness of Pop II low-mass dwarf stars shall naturally lead to similar Li depletion over a large domain in the [Fe/H]–Teff plane, resulting in a plateau with little dispersion. We calibrated the efficiency of the turbulence to fit the abundance of Li in Pop II stars selected from the GALAH DR3 spectroscopic survey and from an homogeneous reanalysis of abundances from the literature. This calibration also enables the reproduction of lithium and magnesium trends in post-turnoff stars of the globular cluster NGC 6752. The same stellar structure considerations consistently explain the observed change of Li depletion and the dispersion regime for [Fe/H] above −1.5 dex, that is, at the transition in metallicity between Pop II to Pop I stars. Conclusions. Our results provide new constraints to the physical processes that transport chemicals and angular momentum in stellar interiors. They offer a comprehensive way to reproduce the observed Li patterns in low-mass dwarf stars across the entire Galactic metallicity range covered by spectroscopic surveys, including the most Fe-poor regime, as supported by the Li value in the non-CEMP star that lies on the plateau at [Fe/H] below −5.8 dex. Our careful analysis of the other very metal-poor stars with lower Li abundances supports the environmental origin of the so-called meltdown regime. Finally, the expected plateau-to-scatter transition pattern further supports the stellar solution to the cosmological problem. [ABSTRACT FROM AUTHOR]

Context. Stellar ages are an important parameter in studies of the chemical evolution of the Galaxy. To better estimate these ages, various methods complementary to the conventional isochrone fitting method have been implemented in the past decade. Several recent studies have established the existence of a relationship between chemical clocks and stellar ages. The [Y/Mg] clock is a promising technique, but there are still several open questions, such as its validity for metal-poor stars and differences between the thin and thick disk populations. Aims. Our aim is to study the relationship between the [Y/Mg] chemical clock and stellar ages for a sample of solar-type disk stars and to provide the empirical dating relation(s) for the stellar age determination from their precise chemical abundances. We also studied the effect of metallicity and populations on this chemical clock. Methods. We derived precise stellar atmospheric parameters as well as the elemental abundances of Mg and Y through line-by-line differential spectroscopic analysis for a sample of 48 metal-poor solar-type stars based on high-quality, high-resolution ESO/HARPS spectra. From high-precision Gaia astrometric data, stellar masses and ages were estimated through isochrone fitting using Yonsei-Yale isochrones. A joint analysis of our sample, together with a sample of 185 solar twins and analogues from our previous works, was performed to calibrate the [Y/Mg] chemical clock in the Galactic disk for −0.71 < [Fe/H] < +0.34. Open clusters and stars with asteroseismic ages were used to validate our relations. Results. Two different populations are clearly seen in the [Mg/Fe]−[Fe/H] plane: the thick and thin disks. Thick disk stars show an age-metallicity relation, whereas the thin disk shows a flatter age–metallicity distribution. We find a strong, metallicity–dependent anti-correlation between the [Y/Mg] ratio and the stellar ages of our sample. For the first time in the literature, we report similar correlations for thin and thick disk stars. Conclusions. We find that the [Y/Mg] relation(s) found here for solar-type stars in a wide metallicity range are compatible with those found for solar twins in the literature. Our relation provides high accuracy and precision (0.45 and 0.99 Gyr, respectively) comparable with the best accuracy achieved for solar twins to date. [ABSTRACT FROM AUTHOR]

Context. The properties of nearby stars bear the imprint of the formation and evolution of the Milky Way (MW). Reconstructing its history requires the determination of precise ages for large samples of stars over long periods. Aims. The present study aims to address the evolution of the MW disc in the region where the Sun and nearby Sun-like stars formed. Methods. The evolution of the disc composition in that region during the last 6 Gyr was inferred from the mean abundances of various chemical elements in nearby Sun-like stars. Their age was estimated from their mean chromospheric activity index using an empirical age–activity relationship derived from stellar rotation period measurements in intermediate-age open clusters. The mean abundances versus age of the sample stars were compared with chemical evolution models of metal-rich gaseous discs experiencing an infall of pristine gas after a quenching period of star formation. Results. The chemical composition of the sample stars reveals two distinct evolutionary trends. Light α elements and iron-peak elements show increasing abundances relative to iron with age. In contrast, the abundance ratios of s-process elements decay with age. Models that best fit the mean abundances of the sample stars as a function of age concur to a gas infall and a concomitant burst of star formation that occurred between 6.2 and 5.5 Gyr ago. Conclusions. This timeline is consistent with a scenario where the first close pericentric passage of the Sagittarius (Sgr) dwarf galaxy ~5.7 Gyr ago induced an infall of metal-poor gas onto the MW disc and a major burst of star formation. The most massive stars that formed in this event rapidly released α elements via type II supernovae explosions, while intermediate-mass stars returned s-process elements on much longer timescales. The first encounter of the Sgr galaxy with the MW played an important role in determining the long-term evolution of the interstellar medium (ISM) composition in the region of the disc where the Sun and Sun-like stars formed, thus explaining the observed correlations between their chemical abundances and their age. [ABSTRACT FROM AUTHOR]

A common property of globular clusters (GCs) is to host multiple populations characterized by peculiar chemical abundances. Recent photometric studies suggest that the He content could vary between the populations of a GC by up to ΔHe ∼ 0.13, in mass fraction. The initial He content impacts the evolution of low-mass stars by ultimately modifying their lifetimes, luminosity, temperatures, and, more generally, the morphology of post-red giant branch (RGB) evolutionary tracks in the Hertzsprung-Russell diagram. We present new physically accurate isochrones with different initial He enrichments and metallicities, with a focus on the methods implemented to deal with the post-RGB phases. The isochrones are based on tracks computed with the stellar evolution code STAREVOL for different metallicities (Z = 0.0002, 0.0009, 0.002, and 0.008) and with a different He enrichment (from 0.25 to 0.6 in mass fraction). We describe the effect of He enrichment on the morphology of the isochrones, and we tested these by comparing the predicted number counts of horizontal branch and asymptotic giant branch stars with those of selected GCs. Comparing the number ratios, we find that our new theoretical ones agree with the observed values within 1σ in most cases. The work presented here sets the ground for future studies on stellar populations in GCs, in which the abundances of light elements in He-enhanced models will rely on different assumptions for the causes of this enrichment. The developed methodology permits the computation of isochrones from new stellar tracks with noncanonical stellar processes. The checked number counts ensure that, at least in this reference set, the contribution of the luminous late stages of stellar evolution to the integrated light of a GC is represented adequately [ABSTRACT FROM AUTHOR]

Aims. The line of sight toward Sk 143 (AzV 456), an O9.5 Ib star in the Small Magellanic Cloud (SMC), shows significant absorption from neutral atoms and molecules. We report a new study of this line of sight by means of high-resolution spectra obtained with the ESPRESSO spectrograph at the VLT of ESO. Methods. The absorption from neutral and ionized species is well characterized by a single component at vhel ≈ +132 km s−1 that was modeled with the ASTROCOOK code. Results. The rubidium Rb I 780.0 nm line is detected for the first time outside the Galaxy, and we derive [Rb/H] = −1.86 ± 0.09. As a result of the high resolution, the 85Rb and 87Rb isotope lines are also exceptionally well resolved. The 85Rb/87Rb isotope ratio is 0.46, which is opposite of the meteoritic value of 2.43. This implies that Rb is made through a dominant contribution of the r-process, which is dominant for the 87Rb isotope. We also confirm the presence of 7Li I 670.7 nm and set a limit on the isotopic ratio of 6Li/7Li < 0.1. Conclusions. The dominance of the 87Rb isotope implies that Rb is made through a dominant contribution of the r-process. At the low metallicity of the cloud of [Zn/H] = −1.28 ± 0.09, neutron rich material may have occurred in rotating metal-poor massive stars. Moreover, the low metallicity of the cloud leads to an absolute Li abundance of A(7Li) ≈ 2.2, which differs from the expectation from big bang nucleosynthesis. Because the gas-phase abundance is not affected by stellar depletion, the burning of Li inside the halo stars is probably not the solution for the cosmological 7Li problem. [ABSTRACT FROM AUTHOR]

Context. Recent works use a linear birth metallicity gradient to estimate the evolution of the [Fe/H] profile in the Galactic disk over time, and infer stellar birth radii (Rbirth) from [Fe/H] and age measurements. These estimates rely on the evolution of [Fe/H] at the Galactic center ([Fe/H](0, τ)) and the birth metallicity gradient (∇[Fe/H](τ)) over time – quantities that are unknown and inferred under key assumptions. Aims. In this work, we use the sample of Milky Way and Andromeda analogues from the TNG50 simulation to investigate the ability to recover [Fe/H](R, τ) in a variety of galaxies. Methods. Using stellar disk particles, we tested the assumptions required in estimating Rbirth, [Fe/H](0, τ), and ∇[Fe/H](τ) using recently proposed methods to understand when they are valid. Results. We show that ∇[Fe/H](τ) can be recovered in most galaxies to within 26% from the range in [Fe/H] across age, with better accuracy for more massive and stronger barred galaxies. We also find that the true central metallicity is unrepresentative of the genuine disk [Fe/H] profile; thus we propose to use a projected central metallicity instead. About half of the galaxies in our sample do not have a continuously enriching projected central metallicity, with a dilution in [Fe/H] correlating with mergers. Most importantly, galaxy-specific [Fe/H](R, τ) can be constrained and confirmed by requiring the Rbirth distributions of mono-age, solar neighborhood populations to follow inside-out formation. Conclusions. We conclude that examining trends with Rbirth is valid for the Milky Way disk and similarly structured galaxies, where we expect Rbirth can be recovered to within 20% assuming today's measurement uncertainties in TNG50. [ABSTRACT FROM AUTHOR]

Context. The existence of low-mass giants with large amounts of lithium (Li) in their surfaces has challenged stellar evolution for decades. One of the possibilities usually discussed in the literature to explain these Li-rich giants involves the interaction with a close binary companion, a scenario that predicts that, when compared against their non-enriched counterparts, Li-rich giants should preferentially be found as part of binary systems. Aims. We aim to assemble the largest possible sample of low-mass giants with well-measured Li abundances, to determine with high statistical significance the close binary fractions of Li-rich and Li-normal giants, and thus test the binary interaction scenario for the emergence of Li-rich giants. Methods. We developed a method that uses radial velocities (RVs) at three different epochs to quantify the degree of RV variability, which we used as a proxy for the presence of a close binary companion. The method was tested and calibrated against samples of known RV standard stars and known spectroscopic binaries. We then assembled a sample of 1418 giants with available RVs from RAVE, GALAH, and Gaia, as well as stellar parameters and Li abundances from GALAH, to which we applied our variability classification. We could determine an evolutionary state for 1030 of these giants. We also compared the results of our RV variability analysis with binarity indicators from the Gaia mission. Results. When applying our methodology to the control samples, we found that the accuracy of the classification is controlled by the precision of the RVs used in the analysis. For the set of RVs available for the giants, this accuracy is 80–85%. Consistent with seismic studies, the resulting sample of giants contains a fraction of Li-rich objects in the red clump (RC) that is twice as large as that in the first ascent red giant branch (RGB). Among RC giants, the fractions of Li-rich objects with a high RV variability and with no RV variability are the same as those for Li-normal objects, but we find some evidence that these fractions may be different for giants in the first-ascent RGB. Analysis of binary indicators in Gaia DR3 shows a smaller fraction of binary giants than our criteria, but no relation can be seen between Li enrichment and binarity either. Conclusions. Our RV variability analysis indicates that there is no preference for Li-rich giants in the RC to be part of binary systems, thus arguing against a binary interaction scenario for the genesis of the bulk of Li-rich giants at that evolutionary stage. On the other hand, Li-rich giants in the RGB appear to have a small but measurable preference for having close companions, something that deserves further scrutiny with more and better data. Additional measurements of the RVs of these giants at a higher RV precision would greatly help in confirming and more robustly quantifying these results. [ABSTRACT FROM AUTHOR]

We combine stellar orbits with the abundances of the heavy, r -process element europium and the light, |$\alpha$| -element, silicon to separate in situ and accreted populations in the Milky Way (MW) across all metallicities. At high orbital energy, the accretion-dominated halo shows elevated values of [Eu/Si], while at lower energies, where many of the stars were born in situ , the levels of [Eu/Si] are lower. These systematically different levels of [Eu/Si] in the MW and the accreted halo imply that the scatter in [Eu/ |$\alpha$| ] within a single galaxy is smaller than previously thought. At the lowest metallicities, we find that both accreted and in situ populations trend down in [Eu/Si], consistent with enrichment via neutron star mergers. Through compiling a large data set of abundances for 54 globular clusters (GCs), we show that differences in [Eu/Si] extend to populations of in situ /accreted GCs. We interpret this consistency as evidence that in r -process elements GCs trace the star formation history of their hosts, motivating their use as sub-Gyr timers of galactic evolution. Furthermore, fitting the trends in [Eu/Si] using a simple galactic chemical evolution model, we find that differences in [Eu/Si] between accreted and in situ MW field stars cannot be explained through star formation efficiency alone. Finally, we show that the use of [Eu/Si] as a chemical tag between GCs and their host galaxies extends beyond the Local Group, to the halo of M31 – potentially offering the opportunity to do Galactic Archaeology in an external galaxy. [ABSTRACT FROM AUTHOR]

In recent years, there has been a push to understand how chemical composition affects the magnetic activity levels of main sequence low-mass stars. Results indicate that more metal-rich stars are more magnetically active for a given stellar mass and rotation period. This metallicity dependence has implications for how the rotation periods and activity levels of low-mass stars evolve over their lifetimes. Numerical modelling suggests that at late ages more metal-rich stars should be rotating more slowly and be more magnetically active. In this work, we study the rotation and activity evolution of low-mass stars using a sample of Kepler field stars. We use the gyro-kinematic age dating technique to estimate ages for our sample and use the photometric activity index as our proxy for magnetic activity. We find clear evidence that, at late ages, more metal-rich stars have spun down to slower rotation in agreement with the theoretical modelling. However, further investigation is required to definitively determine whether the magnetic activity evolution occurs in a metallicity dependent way. [ABSTRACT FROM AUTHOR]

The chemical compositions of stars encode the history of the universe and are thus fundamental for advancing our knowledge of astrophysics and cosmology. However, measurements of elemental abundance ratios, and our interpretations of them, strongly depend on the physical assumptions that dictate the generation of synthetic stellar spectra. Three-dimensional radiation-hydrodynamic (3D RHD) box-in-a-star simulations of stellar atmospheres offer a more realistic representation of surface convection occurring in late-type stars than do traditional one-dimensional (1D) hydrostatic models. As evident from a multitude of observational tests, the coupling of 3D RHD models with line formation in nonlocal thermodynamic equilibrium (non-LTE) today provides a solid foundation for abundance analysis for many elements. This review describes the ongoing and transformational work to advance the state of the art and replace 1D LTE spectrum synthesis with its 3D non-LTE counterpart. In summary: 3D and non-LTE effects are intricately coupled, and consistent modeling thereof is necessary for high-precision abundances; such modeling is currently feasible for individual elements in large surveys. Mean 3D (〈3D〉) models are not adequate as substitutes. The solar abundance debate is presently dominated by choices and systematic uncertainties that are not specific to 3D non-LTE modeling. 3D non-LTE abundance corrections have a profound impact on our understanding of FGK-type stars, exoplanets, and the nucleosynthetic origins of the elements. [ABSTRACT FROM AUTHOR]

We present the stellar value-added catalogue based on the Dark Energy Spectroscopic Instrument (DESI) Early Data Release. The catalogue contains radial velocity and stellar parameter measurements for |$\simeq$| 400 000 unique stars observed during commissioning and survey validation by DESI. These observations were made under conditions similar to the Milky Way Survey (MWS) currently carried out by DESI but also include multiple specially targeted fields, such as those containing well-studied dwarf galaxies and stellar streams. The majority of observed stars have |$16\lt r\lt 20$| with a median signal-to-noise ratio in the spectra of |$\sim$| 20. In the paper, we describe the structure of the catalogue, give an overview of different target classes observed, as well as provide recipes for selecting clean stellar samples. We validate the catalogue using external high-resolution measurements and show that radial velocities, surface gravities, and iron abundances determined by DESI are accurate to 1 km s−1, 0.3 dex, and |$\sim$| 0.15 dex respectively. We also demonstrate possible uses of the catalogue for chemo-dynamical studies of the Milky Way stellar halo and Draco dwarf spheroidal. The value-added catalogue described in this paper is the very first DESI MWS catalogue. The next DESI data release, expected in less than a year, will add the data from the first year of DESI survey operations and will contain approximately 4 million stars, along with significant processing improvements. [ABSTRACT FROM AUTHOR]

Strong metallicity-dependent winds dominate the evolution of core He-burning, classical Wolf–Rayet (cWR) stars, which eject both H and He-fusion products such as |$^{14}$| N, |$^{12}$| C, |$^{16}$| O, |$^{19}$| F, |$^{22}$| Ne, and |$^{23}$| Na during their evolution. The chemical enrichment from cWRs can be significant. cWR stars are also key sources for neutron production relevant for the weak s-process. We calculate stellar models of cWRs at solar metallicity for a range of initial Helium star masses (12–50  |$\rm M_{\odot }$|⁠), adopting recent hydrodynamical wind rates. Stellar wind yields are provided for the entire post-main sequence evolution until core O-exhaustion. While literature has previously considered cWRs as a viable source of the radioisotope |$^{26}$| Al, we confirm that negligible |$^{26}$| Al is ejected by cWRs since it has decayed to |$^{26}$| Mg or proton-captured to |$^{27}$| Al. However, in Paper I, we showed that very massive stars eject substantial quantities of |$^{26}$| Al, among other elements including N, Ne, and Na, already from the zero-age-main-sequence. Here, we examine the production of |$^{19}$| F and find that even with lower mass-loss rates than previous studies, our cWR models still eject substantial amounts of |$^{19}$| F. We provide central neutron densities (N |$_{n}$|⁠) of a 30  |$\rm M_{\odot }$| cWR compared with a 32  |$\rm M_{\odot }$| post-VMS WR and confirm that during core He-burning, cWRs produce a significant number of neutrons for the weak s-process via the |$^{22}$| Ne(⁠|$\alpha$|⁠ ,n) |$^{25}$| Mg reaction. Finally, we compare our cWR models with observed [Ne/He], [C/He], and [O/He] ratios of Galactic WC and WO stars. [ABSTRACT FROM AUTHOR]

To date, we have access to enormous inventories of stellar spectra that allow the extraction of atmospheric parameters and chemical abundances essential in stellar studies. However, characterizing such a large amount of data is complex and requires a good understanding of the studied object to ensure reliable and homogeneous results. In this study, we present a methodology to measure homogenously the basic atmospheric parameters and detailed chemical abundances of over 1600 thin disc main-sequence stars in the 100 pc solar neighbourhood, using APOGEE-2 infrared spectra. We employed the code tonalli to determine the atmospheric parameters using a prior on |$\log {g}$|⁠. The |$\log {g}$| prior in tonalli implies an understanding of the treated population and helps to find physically coherent answers. Our atmospheric parameters agree within the typical uncertainties (100 K in |$\mathrm{T_{eff}}$|⁠ , 0.15 dex in |$\log {g}$| and [M/H]) with previous estimations of ASPCAP and Gaia DR3. We use our temperatures to determine a new infrared colour–temperature sequence, in good agreement with previous works, that can be used for any main-sequence star. Additionally, we used the bacchus code to determine the abundances of Mg, Al, Si, Ca, and Fe in our sample. The five elements (Mg, Al, Si, Ca, Fe) studied have an abundance distribution centred around slightly subsolar values in agreement with previous results for the solar neighbourhood. The over 1600 main-sequence stars' atmospheric parameters and chemical abundances presented here are useful in follow-up studies of the solar neighbourhood or as a training set for data-driven methods. [ABSTRACT FROM AUTHOR]

The prevalence of light element enhancement in the most metal-poor stars is potentially an indication that the Milky Way has a metallicity floor for star formation around |$\sim 10^{-3.5}$| Z |$_{\odot }$|⁠. We propose that this metallicity floor has its origins in metal-enriched star formation in the minihaloes present during the Galaxy's initial formation. To arrive at this conclusion, we analyse a cosmological radiation hydrodynamics simulation that follows the concurrent evolution of multiple Population III star-forming minihaloes. The main driver for the central gas within minihaloes is the steady increase in hydrostatic pressure as the haloes grow. We incorporate this insight into a hybrid one-zone model that switches between pressure-confined and modified free-fall modes to evolve the gas density with time according to the ratio of the free-fall and sound-crossing time-scales. This model is able to accurately reproduce the density and chemo-thermal evolution of the gas in each of the simulated minihaloes up to the point of runaway collapse. We then use this model to investigate how the gas responds to the absence of H |$_{2}$|⁠. Without metals, the central gas becomes increasingly stable against collapse as it grows to the atomic cooling limit. When metals are present in the halo at a level of |$\sim 10^{-3.7}$|  Z |$_{\odot }$|⁠ , however, the gas is able to achieve gravitational instability while still in the minihalo regime. Thus, we conclude that the Galaxy's metallicity floor is set by the balance within minihaloes of gas-phase metal cooling and the radiation background associated with its early formation environment. [ABSTRACT FROM AUTHOR]

Newly-developed spectrographs with increased resolving powers, particularly those covering the near-IR range, allow the characterization of more and more absorption lines in stellar spectra. This includes the identification and confirmation of absorption lines and the calibration of oscillator strengths. In this study, we provide empirical values of |${{\rm log} gf}$| based on the abundances of classical Cepheids obtained with optical spectra to establish the consistency between optical and infrared abundance results. Using time series spectra of classical Cepheids obtained with WINERED spectrograph (0.97–1.35  |$\mu$| m, R |$\sim$| 28000), we demonstrate that we can determine the stellar parameters of the observed Cepheids, including effective temperature (⁠|${T_\mathrm{eff}}$|⁠), surface gravity (⁠|${{\rm log} g}$|⁠), microturbulence (⁠|$\xi$|⁠), and metallicity (⁠|${\rm {[{\mathrm{ M}}/\mathrm{ H}]}}$|⁠). With the newly calibrated relations of line-depth ratios, we can achieve accuracy and precision comparable to optical studies, with uncertainties of |$\sim$| 90 K and 0.108 dex for |${T_\mathrm{eff}}$|⁠ , and |${{\rm log} g}$|⁠ , respectively. Finally, we created a new atlas of absorption lines, featuring precise abundance measurements of various elements found in the atmosphere of Cepheids, including neutron-capture elements whose |${{\rm log} gf}$| values have been astrophysically calibrated. [ABSTRACT FROM AUTHOR]

This second paper presents an in-depth analysis of the composition of the planetary material that has been accreted on to seven white dwarfs with circumstellar dust and gas emission discs with abundances reported in Rogers et al. The white dwarfs are accreting planetary bodies with a wide range of oxygen, carbon, and sulphur volatile contents, including one white dwarf that shows the most enhanced sulphur abundance seen to date. Three white dwarfs show tentative evidence (2–3 |$\sigma$|⁠) of accreting oxygen-rich material, potentially from water-rich bodies, whilst two others are accreting dry, rocky material. One white dwarf is accreting a mantle-rich fragment of a larger differentiated body, whilst two white dwarfs show an enhancement in their iron abundance and could be accreting core-rich fragments. Whilst most planetary material accreted by white dwarfs display chondritic or bulk Earth-like compositions, these observations demonstrate that core-mantle differentiation, disruptive collisions, and the accretion of core-mantle differentiated material are important. Less than 1 per cent of polluted white dwarfs host both observable circumstellar gas and dust. It is unknown whether these systems are experiencing an early phase in the disruption and accretion of planetary bodies, or alternatively if they are accreting larger planetary bodies. From this work there is no substantial evidence for significant differences in the accreted refractory abundance ratios for those white dwarfs with or without circumstellar gas, but there is tentative evidence for those with circumstellar gas discs to be accreting more water rich material which may suggest that volatiles accrete earlier in a gas-rich phase. [ABSTRACT FROM AUTHOR]

Two decades on, the study of hypervelocity stars is still in its infancy. These stars can provide novel constraints on the total mass of the Galaxy and its dark matter distribution. However how these stars are accelerated to such high velocities is unclear. Various proposed production mechanisms for these stars can be distinguished using chemo-dynamic tagging. The advent of Gaia and other large surveys have provided hundreds of candidate hyper velocity objects to target for ground-based high-resolution follow-up observations. We conduct high-resolution spectroscopic follow-up observations of 16 candidate late-type hyper velocity stars using the Apache Point Observatory and the McDonald Observatory. We derive atmospheric parameters and chemical abundances for these stars. We measure up to 22 elements, including the following nucleosynthetic families: |$\alpha$| (Mg, Si, Ca, and Ti), light/odd-Z (Na, Al, V, Cu, and Sc), Fe-peak (Fe, Cr, Mn, Co, Ni, and Zn), and neutron capture (Sr, Y, Zr, Ba, La, Nd, and Eu). Our kinematic analysis shows one candidate is unbound, two are marginally bound, and the remainder are bound to the Galaxy. Finally, for the three unbound or marginally bound stars, we perform orbit integration to locate possible globular cluster or dwarf galaxy progenitors. We do not find any likely candidate systems for these stars and conclude that the unbound stars are likely from the the stellar halo, in agreement with the chemical results. The remaining bound stars are all chemically consistent with the stellar halo as well. [ABSTRACT FROM AUTHOR]

In this paper, a semisupervised machining learning technique had been utilized to analyse low-resolution stellar spectra from Large sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST) Data Release 9 (DR9). We identified approximately 111 000 potential very metal-poor stars. Estimation of their stellar parameters (⁠|$T_{\rm eff}$|⁠ , |${\rm log}\, \rm {g}$|⁠ , [Fe/H]) indicate that over 99 per cent are metal-poor ([Fe/H] < −1.0), comprising 32 631 very metal-poor ([Fe/H] < −2.0), 702 extremely metal-poor ([Fe/H] < −3.0) and 30 ultra metal-poor ([Fe/H] < −4.0) stars. Based on kinematic characteristics, stars were categorized into thick disc-like, thin disc-like, and halo-like groups. We analysed their metallicity distributions (MDs) with respect to vertical height (⁠|$|Z|$|⁠) and orbital eccentricity (e). Thick disc-like stars in current sample show a clear trend of decreasing metallicty with increasing |$|Z|$| or e for the ranges −3.0 |$\lt $| [Fe/H] |$\lt $| −1.2 and |$|Z|$| |$\lt $| 3 kpc. Conversely, thin disc-like stars in current sample exhibit a slight increase in the fraction of more metal-poor stars with |$|Z|$| for the ranges −3.0 |$\lt $| [Fe/H] |$\lt $| −1.2 and |$|Z|$| |$\lt$| 1 kpc, but no obvious correlation with e. Additionally, we confirmed the presence of two prominent substructures among halo-like stars. One exhibits a high eccentricity (⁠|$e\ \gt\ 0.8$|⁠) orbit and higher metallicity, while the other follows a retrograde orbit with moderate eccentricity (⁠|$e\sim 0.6$|⁠) and lower metallicity. We believe they are related to the merger events known as Gaia Sausage and Sequoia, respectively. Furthermore, our observations indicate that the Sequoia has lower eccentricity and metallicity compared to the Gaia Sausage. [ABSTRACT FROM AUTHOR]

Over a quarter of white dwarfs have photospheric metal pollution, which is evidence for recent accretion of exoplanetary material. While a wide range of mechanisms have been proposed to account for this pollution, there are currently few observational constraints to differentiate between them. To investigate the driving mechanism, we observe a sample of polluted and non-polluted white dwarfs in wide binary systems with main-sequence stars. Using the companion stars' metallicities as a proxy for the white dwarfs' primordial metallicities, we compare the metallicities of polluted and non-polluted systems. Because there is a well-known correlation between giant planet occurrence and higher metallicity (with a stronger correlation for close-in and eccentric planets), these metallicity distributions can be used to probe the role of gas giants in white dwarf accretion. We find that the metallicity distributions of polluted and non-polluted systems are consistent with the hypothesis that both samples have the same underlying metallicity distribution. However, we note that this result is likely biased by several selection effects. Additionally, we find no significant trend between white dwarf accretion rates and metallicity. These findings suggest that giant planets are not the dominant cause of white dwarf accretion events in binary systems. [ABSTRACT FROM AUTHOR]

Context. The Gaia Collaboration has recently reported the detection of a 33 M⊙ black hole in a wide binary system located in the solar neighbourhood. Aims. Here we explore the relationship between this black hole, known as Gaia BH3, and the nearby ED-2 halo stellar stream. Methods. We studied the orbital characteristics of the Gaia BH3 binary and present measurements of the chemical abundances of ED-2 member stars derived from high-resolution spectra obtained with the VLT. Results. We find that the Galactic orbit of the Gaia BH3 system and its metallicity are entirely consistent with being part of the ED-2 stream. The characteristics of the stream, particularly its negligible spread in metallicity and in other chemical elements, as well as its single stellar population, suggest that it originated from a disrupted star cluster of low mass. Its age is comparable to that of the globular cluster M92 that has been estimated to be as old as the Universe. Conclusions. This is the first black hole unambiguously associated with a disrupted star cluster. We infer the plausible mass range for the cluster to be relatively narrow, between 2 × 103 M⊙ and 5.2 × 104 M⊙. This implies that the black hole could have formed directly from the collapse of a massive very metal-poor star, but that the alternative scenario of binary interactions inside the cluster environment also deserves to be explored. [ABSTRACT FROM AUTHOR]

Context. Lithium (Li) abundance is an age indicator for G, K, and M stellar types, as its abundance decreases over time for these spectral types. However, despite all of the observational efforts made over the past few decades, the role of rotation, stellar activity, and metallicity in the depletion of Li is still unclear. Aims. Our purpose is to investigate how Li depletion is affected by rotation and metallicity in G and K members of the roughly Pleiades-aged open cluster M35. Methods. We have collected an initial sample of 165 candidate members observed with the WIYN/Hydra spectrograph. In addition, we have taken advantage of three previous spectroscopic studies of Li in M35. As a result, we have collected a final sample of 396 stars observed with the same instrument, which we have classified as non-members, possible non-members, possible members, and probable members of the cluster. We have measured iron abundances, Li equivalent widths, and Li abundances for the 110 M35 members added to the existing sample by this study. Finally, rotation periods for cluster members have been obtained from the literature or derived from Zwicky Transient Facility light curves. Results. We have confirmed that fast G and K rotators are Li-rich in comparison with slow rotators of similar effective temperature. This trend, which is also seen in previous studies, is more evident when binaries are not taken into account. Furthermore, while we derived an average metallicity of [Fe/H] = −0.26 ± 0.09 from our spectra, the distribution of Li in M35 is similar to those observed for the Pleiades and M34 open clusters, which have solar metallicity and slightly different ages. In addition, we have shown that an empirical relationship proposed to remove the contribution of the Fe I line at 670.75 nm to the blended feature at 670.78 nm overestimates by 5–15 mÅ the contribution of this iron line for M35 members. Conclusions. M35 fast G and K rotators have depleted less Li than their slower counterparts. Furthermore, a 0.2−0.3 dex difference in metallicity appears to make little difference in the Li distributions of open clusters with ages between 100 and 250 Myr. [ABSTRACT FROM AUTHOR]

Context. The production of neutron-rich elements at neutron densities intermediate to those of the s- and r-processes, the so-called i-process, has been identified as possibly being responsible for the observed abundance pattern found in certain carbon-enhanced metal-poor (CEMP) stars. The production site may be low-metallicity stars on the asymptotic giant branch (AGB) where the physical processes during the thermal pulses are not well known. Aims. We investigate the impact of overshoot from various convective boundaries during the AGB phase on proton ingestion events (PIEs) and the neutron densities as a necessary precondition for the i-process as well as on the structure and continued evolution of the models. Methods. We therefore analyzed models of a 1.2 M⊙, Z = 5 × 10−5 star. A fiducial model without overshoot on the AGB (overshoot was applied during the pre-AGB evolution) serves as a reference. The same model was then run with various overshoot values and the resulting models were compared to one another. Light element nucleosynthesis is also discussed. Additionally, we introduce a new timescale argument to predict PIE occurrence to discriminate between a physical and a numerical reason for a nonoccurrence. A comparison to observations as well as previous studies was conducted before finally presenting the most promising choice of overshoot parameters for the occurrence of the i-process in low-mass, low-metallicity models. Results. The fiducial model reveals high neutron densities and a persistent split of the pulse-driven convection zone (PDCZ). Overshoot from the PDCZ results in either temporary or permanent remerging of the split PDCZ, influencing the star's structure and evolution. While both overshoot and non-overshoot models exhibit PIEs generating neutron densities suitable for the i-process, they lead to varied C/O and N/O ratios and notable Li enhancements. Comparison with previous studies and observations of CEMP-r/s stars suggests that while surface enhancements in our models may be exaggerated, abundance ratios align well. Though, for high values of overshoot from the PDCZ the agreement becomes worse. [ABSTRACT FROM AUTHOR]

Context. The oldest stars in the Milky Way are metal-poor with [Fe/H] < −1.0, displaying peculiar elemental abundances compared to solar values. The relative variations in the chemical compositions among stars is also increasing with decreasing stellar metallicity, allowing for the pure signature of unique nucleosynthesis processes to be revealed. The study of the r-process is, for instance, one of the main goals of stellar archaeology and metal-poor stars exhibit an unexpected complexity in the stellar production of the r-process elements in the early Galaxy. Aims. In this work, we report the atmospheric parameters, main dynamic properties, and the abundances of four metal-poor stars: HE 1523-0901, HD 6268, HD 121135, and HD 195636 (−1.5 > [Fe/H] > −3.0). Methods. The abundances were derived from spectra obtained with the HRS echelle spectrograph at the Southern African Large Telescope, using both local and non-local thermodynamic equilibrium (LTE and NLTE) approaches, with the average error between 0.10 and 0.20 dex. Results. Based on their kinematical properties, we show that HE 1523-0901 and HD 195636 are halo stars with typical high velocities. In particular, HD 121135 displays a peculiar kinematical behaviour, making it unclear whether it is a halo or an accreted star. Furthermore, HD 6268 is possibly a rare prototype of very metal-poor thick disk stars. The abundances derived for our stars are compared with theoretical stellar models and with other stars with similar metallicity values from the literature. Conclusions. HD 121135 is Al-poor and Sc-poor, compared to stars observed in the same metallicity range (−1.62 > [Fe/H] > −1.12). The most metal-poor stars in our sample, HE 1523-0901, HD 6268, and HD 195636, exhibit anomalies that are better explained by supernova models from fast-rotating stellar progenitors for elements up to the Fe group. Compared to other stars in the same metal-licity range, their common biggest anomaly is represented by the low Sc abundances. If we consider the elements beyond Zn, HE 1523-0901 can be classified as an r-II star, HD 6268 as an r-I candidate, and HD 195636 and HD 121135 exhibiting a borderline r-process enrichment between limited-r and r-I star. Significant relative differences are observed between the r-process signatures in these stars. [ABSTRACT FROM AUTHOR]

Context. An accurate 28P(p, γ)29S reaction rate is crucial to defining the nucleosynthesis products of explosive hydrogen burning in ONe novae. Using the recently released nuclear mass of 29S, together with a shell model and a direct capture calculation, we reanalyzed the 28P(p, γ)29S thermonuclear reaction rate and its astrophysical implication. Aims. We focus on improving the astrophysical rate for 28P(p, γ)29S based on the newest nuclear mass data. Our goal is to explore the impact of the new rate and associated uncertainties on the nova nucleosynthesis. Methods. We evaluated this reaction rate via the sum of the isolated resonance contribution instead of the previously used Hauser-Feshbach statistical model. The corresponding rate uncertainty at different energies was derived using a Monte Carlo method. Nova nucleosynthesis is computed with the 1D hydrodynamic code SHIVA. Results. The contribution from the capture on the first excited state at 105.64 keV in 28P is taken into account for the first time. We find that the capture rate on the first excited state in28 P is up to more than 12 times larger than the ground-state capture rate in the temperature region of 2.5 × 107 K to 4 × 108 K, resulting in the total 28P(p, γ)29S reaction rate being enhanced by a factor of up to 1.4 at ~1 × 109 K. In addition, the rate uncertainty has been quantified for the first time. It is found that the new rate is smaller than the previous statistical model rates, but it still agrees with them within uncertainties for nova temperatures. The statistical model appears to be roughly valid for the rate estimation of this reaction in the nova nucleosynthesis scenario. Using the 1D hydrodynamic code SHIVA, we performed the nucleosynthesis calculations in a nova explosion to investigate the impact of the new rates of 28P(p, γ)29S. Our calculations show that the nova abundance pattern is only marginally affected if we use our new rates with respect to the same simulations but statistical model rates. Finally, the isotopes whose abundance is most influenced by the present 28P(p, γ)29S uncertainty are 28Si, 33,34S, 35,37Cl, and 36Ar, with relative abundance changes at the level of only 3% to 4%. [ABSTRACT FROM AUTHOR]