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Thermohaline mixing is one of the main processes in low-mass red giant stars that affect the transport of chemicals and, thus, the surface abundances along the evolution. The interplay of thermohaline mixing with other processes, such as downward overshooting from the convective envelope, needs to be carefully investigated. This study aims to understand the combined effects of thermohaline mixing and envelope overshooting. After implementing the thermohaline mixing process in the PARSEC stellar evolutionary code, we computed tracks and isochrones (with the TRILEGAL code) and compared them with observational data. To constrain the efficiencies of both processes, we performed detailed modelling that is suitable for globular clusters NGC 6397 and M4. Our results indicate that an envelope overshooting efficiency parameter, Λ_e = 0.6, and a thermohaline efficiency parameter, α_th = 50, are necessary to reproduce the red-giant-branch bump magnitudes and lithium abundances observed in these clusters. We find that both envelope overshooting and thermohaline mixing have a significant impact on the variation in ⁷Li abundances. Additionally, we also explore the effects of adopting solar-scaled or α-enhanced mixtures on our models. The ¹²C and the ¹²C/¹³C ratio are also effective indicators with which to probe extra mixing in red-giant-branch stars. However, their usefulness is currently limited by the lack of precise and accurate C-isotopes abundances.

The role of novae as producers of galactic lithium-7 (Li) has been suggested since the 1970s, and it has been reconsidered recently with the detection of beryllium-7 in their outbursts. At the same time, stellar models are moving forward to help us understand the discrepancy between the primordial Li abundance predicted by the standard Big Bang nucleosynthesis theory and the measured value of old dwarf stars. For this work, we followed the evolution of Li in the Galactic thin disc starting from a primordial value of A(Li)= 2.69 dex and applying Li depletion corrections of the stellar model with overshoot to our chemical evolution models. We used the upper envelope of the observational data to constrain the models. In addition to the dwarf main-sequence (MS) stars, our analysis included, for the first time, the early red-giant-branch (RGB) stars. In addition to the renowned Spite plateau of the MS stars at low metallicities, we also confirm the existence of a second A(Li) plateau of the early RGB stars, which can be explained by our model with the corrections from stellar models. Our best-fit model was obtained with an effective averaged Li yield Y-L(Nova) = 2.34 x 10(-5) M-circle dot during the whole lifetime of a nova. This reinforces the possibility that novae are the main galactic Li source, together with the stellar models' ability to resolve the 'cosmological Li problem' in this context.

Context; The Measuring at Intermediate Metallicity Neutron-Capture Elements (MINCE) project aims to provide high-quality neutron-capture abundances measurements for several hundred stars at an intermediate metallicity of -2.5 < [Fe/H] < -1.5. This project will shed light on the origin of the neutron-capture elements and the chemical enrichment of the Milky Way.

Aims: The goal of this work is to chemically characterize the second sample of the MINCE project and compare the abundances with the galactic chemical evolution model at our disposal.

Methods: We performed a standard abundance analysis based on one-dimensional (1D) local thermodynamic equilibrium (LTE) model atmospheres based on high-resolution and high-signal-to-noise-ratio (S/N) spectra from Ultraviolet and Visual Echelle Spectrograph (UVES).

Results: We provide the kinematic classification (i.e., thin disk, thick disk, thin-to-thick disk, halo, Gaia Sausage Enceladus, Sequoia) of 99 stars and the atmospheric parameters for almost all stars. We derived the abundances for light elements (from Na to Zn) and neutron-capture elements (Rb, Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, and Eu) for a subsample of 32 stars in the metallicity range of -2.5 < [Fe/H] < -1.00. In the subsample of 32 stars, we identified eight active stars exhibiting (inverse) P-Cygni profile and one Li-rich star, CD 28-11039. We find a general agreement between the chemical abundances and the stochastic model computed for the chemical evolution of the Milky Way halo for elements Mg, Ca, Si, Ti, Sc, Mn, Co, Ni, Zn, Rb, Sr, Y, Zr, Ba, La, and Eu .

Conclusions: The MINCE project has already significantly increased the number of neutron-capture elements measurements in the intermediate metallicity range. The results from this sample are in perfect agreement with the previous MINCE sample. The good agreement between the chemical abundances and the chemical evolution model of the Galaxy supports the nucleosynthetic processes adopted to describe the origin of the n-capture elements.

PARSEC v2.0 rotating stellar tracks were previously presented for six metallicity values from subsolar to solar values, with initial rotation rates (ω_i, defined as the ratio of the angular velocity and its critical value) spanning from the non-rotating case to very near the critical velocity (i.e. ω_i = 0.99), and for initial masses covering the ∼0.7 M_⊙ to 14 M_⊙ interval. Furthermore, we provided the corresponding isochrones converted into several photometric systems for different inclination angles between the line-of-sight and the rotation axes, from 0° (pole-on) to 90° (equator-on). In this work, we expand this database with seven other metallicity sets, including five sets of low metallicity (Z = 0.0001 - 0.002) and two sets of super-solar values (up to Z = 0.03). We present the new stellar tracks, which comprise ∼3040 tracks in total (∼5500 including previous sets), along with the new corresponding rotating isochrones. We also introduce the possibility of creating isochrones by interpolation for values of rotating rates that were not available in the initial set of tracks. We compared a selection of our new models with rotating stellar tracks from the Geneva Stellar Evolution Code, and we assessed the quality of our new tracks by fitting the colour-magnitude diagram of the open cluster NGC 6067. We took advantage of the projected rotational velocity of member stars measured by Gaia to validate our results and examined the surface oxygen abundances in comparison with the observed data. All newly computed stellar tracks and isochrones can be retrieved via our dedicated web databases and interfaces.

Context. Metal-poor stars play a crucial role in understanding the nature and evolution of the first stellar generation in the Galaxy. Previously, asteroseismic characterisation of red-giant stars has relied on constraints from the global asteroseismic parameters and not the full spectrum of individual oscillation modes. Using the latter, we present for the first time the characterisation of two evolved very metal-poor stars including the detail-rich mixed-mode patterns. Aims. We will demonstrate that incorporating individual frequencies into grid-based modelling of red-giant stars enhances its precision, enabling detailed studies of these ancient stars and allowing us to infer the stellar properties of two very metal-poor [Fe/H] similar to -2.5 dex Kepler stars: KIC 4671239 and KIC 7693833. Methods. Recent developments in both observational and theoretical asteroseismology have allowed for detailed studies of the complex oscillation pattern of evolved giants. In this work, we employ Kepler timeseries and surface properties from high-resolution spectroscopic data within a grid-based modelling approach to asteroseismically characterise KIC 4671239 and KIC 7693833 using the BAyesian STellar Algorithm, BASTA. Results. Both stars show agreement between constraints from seismic and classical observables, an overlap unrecoverable when purely considering the global asteroseismic parameters. KIC 4671239 and KIC 7693833 were determined to have masses of 0.78(-0.03)(+0.04)and 0.83(-0.01)(+0.03)Mwith ages of12.1(-1.5)(+1.6)and 10.3(-1.4)(+0.6)Gyr, respectively. Particularly, for KIC 4671239 the rich spectrum of model frequencies closely matches the observed. Conclusions. A discrepancy between the observed and modelled nu max of similar to 10% was found, indicating a metallicity dependence of the nu max scaling relation. For metal-poor populations, this results in overestimations of the stellar masses and wrongful age inferences. Utilising the full spectra of individual oscillation modes lets us circumvent the dependence on the asteroseismic scaling relations through direct constraints on the stars themselves. This allows us to push the boundaries of state-of-the-art detailed modelling of evolved stars at metallicities far different from solar.

The first generation of ELT instruments includes an optical-infrared high resolution spectrograph, indicated as ELT-HIRES and recently christened ANDES (ArmazoNes high Dispersion Echelle Spectrograph). ANDES consists of three fibre-fed spectrographs ([U]BV, RIZ, YJH) providing a spectral resolution of similar to 100,000 with a minimum simultaneous wavelength coverage of 0.4-1.8 mu m with the goal of extending it to 0.35-2.4 mu m with the addition of an U arm to the BV spectrograph and a separate K band spectrograph. It operates both in seeing- and diffraction-limited conditions and the fibre-feeding allows several, interchangeable observing modes including a single conjugated adaptive optics module and a small diffraction-limited integral field unit in the NIR. Modularity and fibre-feeding allows ANDES to be placed partly on the ELT Nasmyth platform and partly in the Coude room. ANDES has a wide range of groundbreaking science cases spanning nearly all areas of research in astrophysics and even fundamental physics. Among the top science cases there are the detection of biosignatures from exoplanet atmospheres, finding the fingerprints of the first generation of stars, tests on the stability of Nature's fundamental couplings, and the direct detection of the cosmic acceleration. The ANDES project is carried forward by a large international consortium, composed of 35 Institutes from 13 countries, forming a team of almost 300 scientists and engineers which include the majority of the scientific and technical expertise in the field that can be found in ESO member states.

Context: Gravitational waves from black-hole (BH) merging events have revealed a population of extra-galactic BHs residing in short-period binaries with masses that are higher than expected based on most stellar evolution models - and also higher than known stellar-origin black holes in our Galaxy. It has been proposed that those high-mass BHs are the remnants of massive metal-poor stars.

Aims: Gaia astrometry is expected to uncover many Galactic wide-binary systems containing dormant BHs, which may not have been detected before. The study of this population will provide new information on the BH-mass distribution in binaries and shed light on their formation mechanisms and progenitors.

Methods: As part of the validation efforts in preparation for the fourth Gaia data release (DR4), we analysed the preliminary astrometric binary solutions, obtained by the Gaia Non-Single Star pipeline, to verify their significance and to minimise false-detection rates in high-mass-function orbital solutions.

Results: The astrometric binary solution of one source, Gaia BH3, implies the presence of a 32.70 ± 0.82 M_⊙ BH in a binary system with a period of 11.6 yr. Gaia radial velocities independently validate the astrometric orbit. Broad-band photometric and spectroscopic data show that the visible component is an old, very metal-poor giant of the Galactic halo, at a distance of 590 pc.

Conclusions: The BH in the Gaia BH3 system is more massive than any other Galactic stellar-origin BH known thus far. The low metallicity of the star companion supports the scenario that metal-poor massive stars are progenitors of the high-mass BHs detected by gravitational-wave telescopes. The Galactic orbit of the system and its metallicity indicate that it might belong to the Sequoia halo substructure. Alternatively, and more plausibly, it could belong to the ED-2 stream, which likely originated from a globular cluster that had been disrupted by the Milky Way.

Context. Most of the studies on the determination of the chemical composition of metal-poor stars have been focused on the search of the most pristine stars, searching for the imprints of the ejecta of the first supernovae. Apart from the rare and very interesting r-enriched stars, few elements are measurable in the very metal-poor stars. On the other hand, a lot of work has been done also on the thin-disc and thick-disc abundance ratios in a metallicity range from [Fe/H]> -1.5 dex to solar. In the available literature, the intermediate metal-poor stars (-2.5<[Fe/H]< -1.5) have been frequently overlooked. The MINCE (Measuring at Intermediate metallicity Neutron-Capture Elements) project aims to gather the abundances of neutron-capture elements but also of light elements and iron peak elements in a large sample of giant stars in this metallicity range. The missing information has consequences for the precise study of the chemical enrichment of our Galaxy in particular for what concerns neutron-capture elements and it will be only partially covered by future multi object spectroscopic surveys such as WEAVE and 4MOST. Aims. The aim of this work is to study the chemical evolution of galactic sub-components recently identified (i.e. Gaia Sausage Enceladus (GSE), Sequoia). Methods. We used high signal-to-noise ratios, high-resolution spectra and standard 1D LTE spectrum synthesis to determine the detailed abundances. Results. We could determine the abundances for up to 10 neutron-capture elements (Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm and Eu) in 33 stars. The general trends of abundance ratios [n-capture element/Fe] versus [Fe/H] are in agreement with the results found in the literature. When our sample is divided in sub-groups depending on their kinematics, we found that the run of [Sr/Ba] versus [Ba/H] for the stars belonging to the GSE accretion event shows a tight anti-correlation. The results for the Sequoia stars, although based on a very limited sample, shows a [Sr/Ba] systematically higher than the [Sr/Ba] found in the GSE stars at a given [Ba/H] hinting at a different nucleosynthetic history. Stochastic chemical evolution models have been computed to understand the evolution of the GSE chemical composition of Sr and Ba. The first conclusions are that the GSE chemical evolution is similar to the evolution of a dwarf galaxy with galactic winds and inefficient star formation. Conclusions. Detailed abundances of neutron-capture elements have been measured in high-resolution, high signal-to-noise spectra of intermediate metal-poor stars, the metallicity range covered by the MINCE project. These abundances have been compared to detailed stochastic models of galactic chemical evolution.

The search for extraterrestrial intelligence is currently being pursued using multiple techniques and in different wavelength bands. Dyson spheres, megastructures that could be constructed by advanced civilizations to harness the radiation energy of their host stars, represent a potential technosignature, that in principle may be hiding in public data already collected as part of large astronomical surveys. In this study, we present a comprehensive search for partial Dyson spheres by analysing optical and infrared observations from Gaia, 2MASS, and WISE. We develop a pipeline that employs multiple filters to identify potential candidates and reject interlopers in a sample of five million objects, which incorporates a convolutional neural network to help identify confusion in WISE data. Finally, the pipeline identifies seven candidates deserving of further analysis. All of these objects are M-dwarfs, for which astrophysical phenomena cannot easily account for the observed infrared excess emission.

The ArmazoNes high Dispersion Echelle Spectrograph (ANDES) is the optical and near-infrared high-resolution echelle spectrograph envisioned for the Extremely Large Telescope (ELT). We present a selection of science cases, supported by new calculations and simulations, where ANDES could enable major advances in the fields of stars and stellar populations. We focus on three key areas, including the physics of stellar atmospheres, structure, and evolution; stars of the Milky Way, Local Group, and beyond; and the star-planet connection. The key features of ANDES are its wide wavelength coverage at high spectral resolution and its access to the large collecting area of the ELT. These features position ANDES to address the most compelling questions and potentially transformative advances in stellar astrophysics of the decades ahead, including questions which cannot be anticipated today.