Search

We present theoretical mass estimates of $^{26}$Al and $^{60}$Fe throughout the Galaxy, performed with a numerical chemical evolution model including detailed nucleosynthesis prescriptions for stable and radioactive nuclides. We compared the results for several sets of stellar yields taken from the literature, for massive, low and intermediate mass stars, nova systems (only for $^{26}$Al) and supernovae Type Ia.We then computed the total masses of $^{26}$Al and $^{60}$Fe in the Galaxy. We studied the bulge and the disc of the Galaxy in a galactocentric radius range 0-22 kpc. We assumed that the bulge region (within 2 kpc) evolved quickly suffering a strong star formation burst, while the disc formed more slowly and inside-out. We compared our results with the $^{26}$Al mass observed by the $\gamma$-ray surveys COMPTEL and INTEGRAL to select the best model. Concerning $^{60}$Fe, we do not have any observed mass value so we just performed a theoretical prediction for future observations. In conclusion, low, intermediate mass stars and Type Ia supernovae contribute negligibly to the two isotopes, while massive stars are the dominant source. The nova contribution is, however, necessary to reproduce the observations of $^{26}$Al. Our best model predicts $2.12$ M$_{\odot}$ of $^{26}$Al, in agreement with observations, while for $^{60}$Fe our best mass estimate is $\sim 1.05$ M$_{\odot}$. We also predicted the present injection rate of $^{26}$Al and $^{60}$Fe in the Galaxy and compared it with previous results, and we found a larger present time injection rate along the disc., Comment: accepted,10 pages, 6 figures

The recurrent nova RS Oph underwent a new outburst on August 8, 2021, reaching a visible brightness of V = 4.8 mag. Observations of the 2021 outburst made with the high resolution UVES spectrograph at the Kueyen-UT2 telescope of ESO-VLT in Paranal enabled detection of the possible presence of 7Be freshly made in the thermonuclear runaway reactions. The 7Be yields can be estimated in N(Be)/N(H) = 5.7 x 10^(-6), which are close to the lowest yields measured in classical novae so far. 7Be is short-lived and decays only into 7Li. By means of a spectrum taken during the nebular phase we estimated an ejected mass of about 1.1 x 10^(-5) Msun, providing an amount of about 4.4x 10^(-10) Msun of 7Li created in the 2021 event. Recurrent novae of the kind of RS Oph may synthesize slightly lower amount of 7Li per event as classical novae, but occur 10^3 times more frequently. The recurrent novae fraction is in the range of 10-30% and they could have contributed to the making of 7Li we observe today. The detection of 7Be in RS Oph provides further support to the recent suggestion that novae are the most effective source of 7Li in the Galaxy., Accepted 2022 September 17. Received 2022 September 16; in original form 2022 April 20. 12 pages, 13 figures

Support from the Centre National d’Etudes Spatiales (CNES), France. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Support of ESO, OCA, and CNES is acknowledged for the AMBRE project. Some of the calculations have been performed with the high-performance computing facility SIGAMM, hosted by OCA. CA acknowledges partial support by project PGC2018-095317-B-C21 financed by the MCIN/AEI FEDER ‘Una manera de hacer Europa’, and by project PID2021-123110NB-I00 financed by MCIN/AEI /10.13039/501100011033/FEDER, UE, Using a semi-analytical model of the evolution of the Milky Way, we show how secular evolution can create distinct overdensities in the phase space of various properties (e.g. age versus metallicity or abundance ratios versus age) corresponding to the thin and thick discs. In particular, we show how key properties of the Solar vicinity can be obtained by secular evolution, with no need for external or special events, like galaxy mergers or paucity in star formation. This concerns the long established double-branch behaviour of [alpha/Fe] versus metallicity and the recently found non-monotonic evolution of the stellar abundance gradient, evaluated at the birth radii of stars. We extend the discussion to other abundance ratios and we suggest a classification scheme, based on the nature of the corresponding yields (primary versus secondary or odd elements) and on the lifetimes of their sources (short-lived versus long-lived ones). The latter property is critical in determining the single- or double- branch behaviour of an elementary abundance ratio in the Solar neighbourhood. We underline the high diagnostic potential of this finding, which can help to separate clearly elements with sources evolving on different time-scales and help determining the site of e.g. the r-process(es). We define the ‘abundance distance’ between the thin and thick disc sequences as an important element for such a separation. We also show how the inside-out evolution of the Milky Way disc leads rather to a single-branch behaviour in other disc regions., Centre National d’Etudes Spatiales (CNES), Gaia Data Processing and Analysis Consortium DPAC, European Space Agency ESA, Centre National d’Etudes Spatiales PGC2018-095317-B-C21 CNES, Ministerio de Ciencia e Innovación MICINN, Agencia Estatal de Investigación PID2021-123110NB-I00 AEI

In this study we combine asteroseismic, spectroscopic and kinematic information to perform a detailed analysis of a sample of 16 stars from the Kepler field. Our selection focuses on stars that appear to contradict Galactic chemical evolution models: young and $\alpha$-rich, old and metal-rich, as well as other targets with unclear classification in past surveys. Kinematics are derived from Gaia DR3 parallaxes and proper motions, and high-resolution spectra from HIRES/Keck are used to calculate chemical abundances for over 20 elements. This information is used to perform careful checks on asteroseismic masses and ages derived via grid-based modelling. Among the seven stars previously classified as young and $\alpha$-rich, only one seems to be an unambiguously older object masking its true age. We confirm the existence of two very old ($\geq$11 Gyr), super metal rich ($\geq$0.1 dex) giants. These two stars have regular thin disc chemistry and in-plane solar circle orbits which fit well in the picture of radial migration via the churning mechanism. The alternative explanation that these stars have younger ages would require mass-loss rates which strongly increases with increasing metallicity. Finally, we suggest further investigations to explore the suitability of Zn as a chemical clock in red giants., Comment: 10 pages, 7 figures, accepted for publication in MNRAS

A renewed interest about the origin of \emph{r}-process elements has been stimulated by the multi-messenger observation of the gravitational event GW170817, with the detection of both gravitational waves and electromagnetic waves corresponding to the merger of two neutron stars. Such phenomenon has been proposed as one of the main sources of the \emph{r}-process. However, the origin of the \emph{r}-process elements at different metallicities is still under debate. We aim at investigating the origin of the \emph{r}-process elements in the Galactic thin disc population. From the sixth internal data release of the \emph{Gaia}-ESO we have collected a large sample of Milky Way thin- and thick-disc stars for which abundances of Eu, O, and Mg are available. The sample consists of members of 62 open clusters, located at a Galactocentric radius from $\sim 5$ kpc to $\sim 20$ kpc in the disc, in the metallicity range $[-0.5, 0.4]$ and covering an age interval from 0.1 to 7 Gy, and about 1300 Milky Way disc field stars in the metallicity range $[-1.5, 0.5]$. We compare the observations with the results of a chemical evolution model, in which we varied the nucleosynthesis sources for the three considered elements. Our main result is that Eu in the thin disc is predominantly produced by sources with short lifetimes, such as magneto-rotationally driven SNe. There is no strong evidence for additional sources at delayed times. Our findings do not imply that there cannot be a contribution from mergers of neutron stars in other environments, as in the halo or in dwarf spheroidal galaxies, but such a contribution is not needed to explain Eu abundances at thin disc metallicities., 20 pages, accepted for publication in A&A

Since the advent of $Gaia$ astrometry, it is possible to identify massive accreted systems within the Galaxy through their unique dynamical signatures. One such system, $Gaia$-Sausage-Enceladus (GSE), appears to be an early "building block" given its virial mass $> 10^{10}\,\mathrm{M_\odot}$ at infall ($z\sim1-3$). In order to separate the progenitor population from the background stars, we investigate its chemical properties with up to 30 element abundances from the GALAH+ Survey Data Release 3 (DR3). To inform our choice of elements for purely chemically selecting accreted stars, we analyse 4164 stars with low-$��$ abundances and halo kinematics. These are most different to the Milky Way stars for abundances of Mg, Si, Na, Al, Mn, Fe, Ni, and Cu. Based on the significance of abundance differences and detection rates, we apply Gaussian mixture models to various element abundance combinations. We find the most populated and least contaminated component, which we confirm to represent GSE, contains 1049 stars selected via [Na/Fe] vs. [Mg/Mn] in GALAH+ DR3. We provide tables of our selections and report the chrono-chemodynamical properties (age, chemistry, and dynamics). Through a previously reported clean dynamical selection of GSE stars, including $30 < \sqrt{J_R~/~\mathrm{kpc\,km\,s^{-1}}} < 55$, we can characterise an unprecedented 24 abundances of this structure with GALAH+ DR3. Our chemical selection allows us to prevent circular reasoning and characterise the dynamical properties of the GSE, for example mean $\sqrt{J_R~/~\mathrm{kpc\,km\,s^{-1}}} = 26_{-14}^{+9}$. We find only $(29\pm1)\%$ of the GSE stars within the clean dynamical selection region. Our methodology will improve future studies of accreted structures and their importance for the formation of the Milky Way., 29 pages, 18 figures, 6 tables; publicshed in MNRAS; all code to recreate results (based on public data described in arXiv:2011.02505) and figures available at https://github.com/svenbuder/Accreted-stars-in-GALAH-DR3

Using data from the GALAH survey, we explore the dependence of elemental abundances on stellar age and metallicity among Galactic disc stars. We find that the abundance of most elements can be predicted from age and [Fe/H] with an intrinsic scatter of about 0.03 dex. We discuss the possible causes for the existence of the abundance-age-metallicity relations. Using a stochastic chemical enrichment scheme based on the size of Supernovae remnants, we show the intrinsic scatter is expected to be small, about 0.05 dex or even smaller if there is additional mixing in the ISM. Elemental abundances show trends with both age and metallicity and the relationship is well described by a simple model in which the dependence of abundance ([X/Fe]) on age and [Fe/H] are additively separable. Elements can be grouped based on the direction of their abundance gradient in the (age,[Fe/H]) plane and different groups can be roughly associated with three distinct nucleosynthetic production sites, the exploding massive stars, the exploding white dwarfs and the AGB stars. However, the abundances of some elements, like Co, La, and Li, show large scatter for a given age and metallicity, suggesting processes other than simple Galactic chemical evolution are at play. We also compare the abundance trends of main-sequence turn-off stars against that of giants, whose ages were estimated using asteroseismic information from the K2 mission. For most elements, the trends of main-sequence turn-off stars are similar to that of giants. The existence of abundance relations implies that we can estimate the age and birth radius of disc stars, which is important for studying the dynamic and chemical evolution of the Galaxy., Comment: 21 pages, 11 Figures

Large fractions of metals are missing from the observable gas-phase in the interstellar medium (ISM) because they are incorporated into dust grains, a phenomenon called dust depletion. The study of dust depletion in the ISM is important to investigate the origin and evolution of metals and cosmic dust. Here we aim at characterizing the dust depletion of several metals from the Milky Way to distant galaxies. We collect ISM metal column densities from absorption-line spectroscopy in the literature, and in addition, we determine Ti and Ni column densities from a sample of 70 damped Lyman-$\alpha$ absorbers (DLAs) towards quasars, observed with UVES/VLT. We use ISM relative abundances to estimate the dust depletion of 18 metals (C, P, O, Cl, Kr, S, Ge, Mg, Si, Cu, Co, Mn, Cr, Ni, Al, Ti, Zn and Fe) for different environments (the Milky Way, the Magellanic Clouds (MCs), DLAs towards quasars and towards gamma-ray bursts). We observe linear relations between the depletion of each metal and the strength of dust depletion, which we trace with the observed [Zn/Fe]. In the neutral ISM of the MCs we find small deviations from linearity observed as an overabundance of the $\alpha$-elements Ti, Mg, S and an underabundance of Mn. The deviations disappear if we assume that all OB stars observed towards the MCs in our sample have an $\alpha$-element enhancement and Mn underabundance. This may imply that the MCs have been recently enriched in $\alpha$-elements, potentially due to recent bursts of star formation. The observed strong correlations of the depletion sequences of the metals all the way from low metallicity QSO-DLAs to the Milky Way suggest that cosmic dust has a common origin, independently of the star formation history, which varies significantly between these different galaxies. This supports the importance of grain growth in the ISM as a significant process of dust production., Comment: 30 pages, 35 figures, 12 tables, Accepted for publication in A&A, Abstract abridged for arXiv

We aim to prepare the machine-learning ground for the next generation of spectroscopic surveys, such as 4MOST and WEAVE. Our goal is to show that convolutional neural networks can predict accurate stellar labels from relevant spectral features in a physically meaningful way. We built a neural network and trained it on GIRAFFE spectra with associated stellar labels from the sixth internal Gaia-ESO data release. Our neural network predicts the atmospheric parameters Teff and log(g) as well as the chemical abundances [Mg/Fe], [Al/Fe], and [Fe/H] for 30115 stellar spectra. The scatter of predictions from eight slightly different network models shows a high internal precision of the network results: 24 K for Teff, 0.03 for log(g), 0.02 dex for [Mg/Fe], 0.03 dex for [Al/Fe], and 0.02 dex for [Fe/H]. The network gradients reveal that the network is inferring the labels in a physically meaningful way from spectral features. Validation with benchmark stars and several scientific applications confirm that our network predictions are accurate for individual stars and recover the properties of different stellar populations in the Milky Way galaxy. Such a study provides very good insights into the application of machine-learning for the spectral analysis of large-scale spectroscopic surveys, such as WEAVE and 4MIDABLE-LR and -HR (4MOST Milky Way disk and bulge low- and high-resolution). The community will have to put a substantial effort into building proactive training sets for machine-learning methods to minimize the possible systematics., Submitted to A&A

Gaia DR3 opens a new era of all-sky spectral analysis of stellar populations thanks to the nearly 5.6 million stars observed by the RVS and parametrised by the GSP-spec module. The all-sky Gaia chemical cartography allows a powerful and precise chemo-dynamical view of the Milky Way with unprecedented spatial coverage and statistical robustness. First, it reveals the strong vertical symmetry of the Galaxy and the flared structure of the disc. Second, the observed kinematic disturbances of the disc -- seen as phase space correlations -- and kinematic or orbital substructures are associated with chemical patterns that favour stars with enhanced metallicities and lower [alpha/Fe] abundance ratios compared to the median values in the radial distributions. This is detected both for young objects that trace the spiral arms and older populations. Several alpha, iron-peak elements and at least one heavy element trace the thin and thick disc properties in the solar cylinder. Third, young disc stars show a recent chemical impoverishment in several elements. Fourth, the largest chemo-dynamical sample of open clusters analysed so far shows a steepening of the radial metallicity gradient with age, which is also observed in the young field population. Finally, the Gaia chemical data have the required coverage and precision to unveil galaxy accretion debris and heated disc stars on halo orbits through their [alpha/Fe] ratio, and to allow the study of the chemo-dynamical properties of globular clusters. Gaia DR3 chemo-dynamical diagnostics open new horizons before the era of ground-based wide-field spectroscopic surveys. They unveil a complex Milky Way that is the outcome of an eventful evolution, shaping it to the present day (abridged)., Astronomy and Astrophysics (accepted, in press)

The recent Gaia Third Data Release contains a homogeneous analysis of millions of high-quality Radial Velocity Spectrometer (RVS) stellar spectra by the GSP-Spec module. This led to the estimation of millions of individual chemical abundances and allows us to chemically map the Milky Way. Among the published GSP-Spec abundances, three heavy-elements produced by neutron-captures in stellar interiors can be found: Ce, Zr and Nd. We use a sample of about 30,000 LTE Ce abundances, selected after applying different combinations of GSP-Spec flags. Thanks to the Gaia DR3 astrometric data and radial velocities, we explore the cerium content in the Milky Way and, in particular, in its halo and disc components. The high quality of the Ce GSP-Spec abundances is quantified thanks to literature comparisons. We found a rather flat [Ce/Fe] versus [M/H] trend. We also found a flat radial gradient in the disc derived from field stars and, independently, from about 50 open clusters, in agreement with previous studies. The [Ce/Fe] vertical gradient has also been estimated. We also report an increasing [Ce/Ca] vs [Ca/H] in the disc, illustrating the late contribution of AGB with respect to SN II. Our cerium abundances in the disc, including the young massive population, are well reproduced by a new three-infall chemical evolution model. Among the halo population, the M 4 globular cluster is found to be enriched in cerium. Moreover, eleven stars with cerium abundances belonging to the Thamnos, Helmi Stream and Gaia-Sausage-Enceladus accreted systems were identified from chemo-dynamical diagnostics. We found that the Helmi Stream could be slightly underabundant in cerium, compared to the two other systems. This work illustrates the high quality of the GSP-Spec chemical abundances, that significantly contributes to unveil the heavy elements evolution history of the Milky Way., 17 pages, 12 figures, accepted by A&A

In this Thesis, we investigate the chemical and dust evolution of the different galactic environments we encounter during the cosmic history, from the high-redshift Universe to the Milky Way. The study of the evolution of galaxies is performed by means of detailed chemical evolution models that predict the abundances of single chemical elements in the interstellar medium as well as the condensation into dust of the chemical elements. In the first part of the Thesis, we concentrate on the study of moderate to high-redshift systems. We start focusing on high-redshift starburst galaxies, whose extreme conditions pose questions on the universality of the initial mass function (IMF) as well as on the processes regulating the ISM dust. For these reasons, we test the the impact of the IMF shape on high-redshift environments by applying the so-called Integrated Galactic IMF (IGIMF) theory in models specifically suited for starburst galaxies. In this way, we look at the interplay between the IMF and dust processes in shaping the observed gas abundance patterns as well as global dust quantities. This analysis highlights the degenerate effect of the IGIMF and dust on abundance patterns and suggests that the IGIMF can explain the dust masses observed in some high-redshift star forming objects. To get a more complete picture about dust through cosmic evolution, we also investigate how dust quantities evolve at larger volume scales. To this aim, we present a novel method to compute the redshift evolution of dust mass in galaxy clusters. This is done by integrating the predictions of chemical and dust evolution models for individual galaxies over the galaxy cluster luminosity function (LF), assuming suitable cosmological scenarios for the LF evolution. By applying this method, we reproduce the dust amounts observed in low and intermediate-redshift galaxy clusters and we answer to some questions about dust in cluster. In particular, we find that spiral galaxies are the most important dust producers within clusters and that galactic ejecta can account alone for the observed intracluster dust. In the second part of the Thesis, instead, we focus on study of the local Universe and in particular of the MW Galaxy. We start investigating the evolution of the MW thick and thin discs by comparing MW models with recent survey data. In particular, we discuss the formation of abundance gradients in the MW and the main physical parameters influencing this process, concluding that inside-out disc formation should act together with radial gas flows and variable efficiency of star formation. Moreover, we suggest that to reproduce the observed [α/Fe] dichotomy/bimodality (i.e., the presence of two distinct data sequences in the [α/Fe] vs. [Fe/H] diagram) at different Galactocentric distances, one should assume a prolonged gap between the formation of the thick and thin discs and a chemically enriched gas accretion in the innermost thin disc. Finally, we study the impact of different Type Ia SN yields on the evolution of Fe-peak elements in our Galaxy. To this aim, we apply to our chemical models for the MW a large compilation of Type Ia SN yields from the recent literature, sampling different explosion mechanisms. The obtained results are compared with those obtained with classical Type Ia SN prescriptions adopted in previous studies. In addition, we allow combinations of of Type Ia SN yields from different progenitor classes to assess their role in terms of the chemical enrichment. We find that the chemical abundance patterns strongly depend not only on the explosion mechanism but also on other conditions. Moreover, the comparison with the observed abundance trends suggests that a combination of different classes of explosion is necessary to reproduce the data. In this Thesis, we investigate the chemical and dust evolution of the different galactic environments we encounter during the cosmic history, from the high-redshift Universe to the Milky Way. The study of the evolution of galaxies is performed by means of detailed chemical evolution models that predict the abundances of single chemical elements in the interstellar medium as well as the condensation into dust of the chemical elements. In the first part of the Thesis, we concentrate on the study of moderate to high-redshift systems. We start focusing on high-redshift starburst galaxies, whose extreme conditions pose questions on the universality of the initial mass function (IMF) as well as on the processes regulating the ISM dust. For these reasons, we test the the impact of the IMF shape on high-redshift environments by applying the so-called Integrated Galactic IMF (IGIMF) theory in models specifically suited for starburst galaxies. In this way, we look at the interplay between the IMF and dust processes in shaping the observed gas abundance patterns as well as global dust quantities. This analysis highlights the degenerate effect of the IGIMF and dust on abundance patterns and suggests that the IGIMF can explain the dust masses observed in some high-redshift star forming objects. To get a more complete picture about dust through cosmic evolution, we also investigate how dust quantities evolve at larger volume scales. To this aim, we present a novel method to compute the redshift evolution of dust mass in galaxy clusters. This is done by integrating the predictions of chemical and dust evolution models for individual galaxies over the galaxy cluster luminosity function (LF), assuming suitable cosmological scenarios for the LF evolution. By applying this method, we reproduce the dust amounts observed in low and intermediate-redshift galaxy clusters and we answer to some questions about dust in cluster. In particular, we find that spiral galaxies are the most important dust producers within clusters and that galactic ejecta can account alone for the observed intracluster dust. In the second part of the Thesis, instead, we focus on study of the local Universe and in particular of the MW Galaxy. We start investigating the evolution of the MW thick and thin discs by comparing MW models with recent survey data. In particular, we discuss the formation of abundance gradients in the MW and the main physical parameters influencing this process, concluding that inside-out disc formation should act together with radial gas flows and variable efficiency of star formation. Moreover, we suggest that to reproduce the observed [α/Fe] dichotomy/bimodality (i.e., the presence of two distinct data sequences in the [α/Fe] vs. [Fe/H] diagram) at different Galactocentric distances, one should assume a prolonged gap between the formation of the thick and thin discs and a chemically enriched gas accretion in the innermost thin disc. Finally, we study the impact of different Type Ia SN yields on the evolution of Fe-peak elements in our Galaxy. To this aim, we apply to our chemical models for the MW a large compilation of Type Ia SN yields from the recent literature, sampling different explosion mechanisms. The obtained results are compared with those obtained with classical Type Ia SN prescriptions adopted in previous studies. In addition, we allow combinations of of Type Ia SN yields from different progenitor classes to assess their role in terms of the chemical enrichment. We find that the chemical abundance patterns strongly depend not only on the explosion mechanism but also on other conditions. Moreover, the comparison with the observed abundance trends suggests that a combination of different classes of explosion is necessary to reproduce the data.

In this work we combine information from solar-like oscillations, high-resolution spectroscopy and Gaia astrometry to derive stellar ages, chemical abundances and kinematics for a group of seven metal-poor Red Giants and characterise them in a multidimensional chrono-chemo-dynamical space. Chemical abundance ratios were derived through classical spectroscopic analysis employing 1D LTE atmospheres on Keck/HIRES spectra. Stellar ages, masses and radii were calculated with grid-based modelling, taking advantage of availability of asteroseismic information from Kepler. The dynamical properties were determined with Galpy using Gaia EDR3 astrometric solutions. Our results suggest that underestimated parallax errors make the effect of Gaia parallaxes more important than different choices of model grid or -- in the case of stars ascending the RGB -- mass-loss prescription. Two of the stars in this study are identified as potentially evolved halo blue stragglers. Four objects are likely members of the accreted Milky Way halo, and their possible relationship with known accretion events is discussed., Comment: 15 pages, 8 figures, accepted for publication in MNRAS

Context. The last decade has seen a revolution in our knowledge of the Galaxy thanks to the Gaia and asteroseismic space missions and the ground-based spectroscopic surveys. Aims. To complete this picture, it is necessary to map the ages of its stellar populations. During recent years, the dependence on time of abundance ratios involving slow (s) neutron-capture and α elements (called chemical-clocks) has been used to provide estimates of stellar ages, usually in a limited volume close to the Sun. We aim to analyse the relations of chemical clocks in the Galactic disc extending the range to RGC ∼ 6–20 kpc. Methods. Using the sixth internal data release of the Gaia-ESO survey, we calibrated several relations between stellar ages and abundance ratios [s/α] using a sample of open clusters, the largest one so far used with this aim (62 clusters). Thanks to their wide galactocentric coverage, we investigated the radial variations of the shape of these relations, confirming their non-universality. Results. The multi-variate relations allowed us to infer stellar ages for field stars. We estimated our accuracy (ranging from 0.0 to −0.9 Gyr) and precision (from 0.4 to 2.3 Gyr) in recovering the global ages of open clusters, and the ages of their individual members. We applied the relations with the highest correlation coefficients to the field star population, finding an older population at lower metallicity and higher [α/Fe] in the thin disc, and a younger one at higher [Fe/H] and low [α/Fe], as expected. Conclusion. We confirm that there is no single age-chemical clock relationship valid for the whole disc, but that there is a dependence on the galactocentric position, which is related to the radial variation of the star formation history combined with the non-monotonic dependence on metallicity of the yields of the s-process elements from low- and intermediate-mass stars. Finally, the abundance ratios [Ba/α] are more sensitive to age than those with [Y/α] for young disc stars, and their slopes vary less with galactocentric distance. We remind the reader that the application of such relationships to field stars is only of statistical value. © ESO 2022., Based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 188.B-3002. These data products have been processed by the Cambridge Astronomy Survey Unit (CASU) at the Institute of Astronomy, University of Cambridge, and by the FLAMES/UVES reduction team at INAF/Osservatorio Astrofisico di Arcetri. These data have been obtained from the Gaia-ESO Survey Data Archive, prepared and hosted by the Wide Field Astronomy Unit, Institute for Astronomy, University of Edinburgh, which is funded by the UK Science and Technology Facilities Council. This work was partly supported by the European Union FP7 programme through ERC grant number 320360 and by the Leverhulme Trust through grant RPG-2012-541. We acknowledge the support from INAF and Ministero dell’ Istruzione, dell’ Università’ e della Ricerca (MIUR) in the form of the grant “Premiale VLT 2012” and “Premiale 2016 MITiC”. The results presented here benefit from discussions held during the Gaia-ESO workshops and conferences supported by the ESF (European Science Foundation) through the GREAT Research Network Programme. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. C.V.V. and L.M. thank the COST Action CA18104: MW-Gaia. T.B. was funded by grant No. 2018-04857 from The Swedish Research Council. F.J.E. acknowledges financial support by the spanish grant PGC2018-101950-B-I00 and MDM-2017-0737 at Centro de Astrobiología (CSIC-INTA), Unidad de Excelencia María de Maeztu, and from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement no. 824064 through the ESCAPE – The European Science Cluster of Astronomy and Particle Physics ESFRI Research Infrastructures project. C.V.V. is especially grateful to Andrés Moya Bedón (University of Valencia) for his support and help. G.C. acknowledges support from the European Research Council Consolidator Grant funding scheme (project ASTEROCHRONOMETRY, G.A. n. 772293, http://www.asterochronometry.eu)., With funding from the Spanish government through the Severo Ochoa Centre of Excellence accreditation SEV-2017-0709.

Context. The [Mg/Fe] abundance ratios are a fundamental fossil signature to trace the chemical evolution of the disc. Despite of the huge observational and theoretical effort, discrepancies between models and data are still present and several explanations have been put forward to explain the [$\alpha$/Fe] bimodality. Aims. In this work, we take advantage of a new AMBRE:HARPS dataset, which provides new and more precise [Mg/Fe] estimations, as well as reliable stellar ages for a subsample of stars, to study the evolution of the solar neighbourhood. Methods. The above data are compared with detailed chemical evolution models for the Milky Way, exploring the most used prescriptions for stellar yields and different formation scenarios for the Galactic disc, i.e. the delayed two-infall and the parallel model, also including prescriptions for stellar radial migration. Results. We see that most of the stellar yields struggle to reproduce the observed trend of the data and that semi-empirical yields are still the best to describe the [Mg/Fe] evolution in the thick and thin discs. In particular, most of the yields still predict a steeper decrease of the [Mg/Fe] ratio at high metallicity than what is shown by the data. The bulk of the data are well reproduced by the parallel and two-infall scenarios, but both scenarios have problems in explaining the most metal-rich and metal-poor tails of the low-$\alpha$ data. These tails can be explained in light of radial migration from inner and outer disc regions, respectively. Conclusions. Despite of the evidence of stellar migration, it is difficult to estimate the actual contribution of stars from other parts of the disc to the solar vicinity. However, the comparison between data and models suggests that peculiar histories of star formation, such as that of the two-infall model, are still needed to reproduce the observed distribution of stars., Comment: 16 pages, 16 figures. Accepted for publication in Astronomy and Astrophysics (A&A)

We report the identification of a set of old super metal-rich dwarf stars with orbits of low eccentricity that reach a maximum height from the Galactic plane between ~0.5-1.5 kpc. We discuss their properties to understand their origins. We use data from the internal data release 6 of the Gaia-ESO Survey. We selected stars observed at high resolution with abundances of 21 species of 18 individual elements. We apply hierarchical clustering to group the stars with similar chemical abundances within the complete chemical abundance space. According to their chemical properties, this set of super metal-rich stars can be arranged into five subgroups. Four seem to follow a chemical enrichment flow, where nearly all abundances increase in lockstep with Fe. The fifth subgroup shows different chemical characteristics. All subgroups have the following features: median ages of the order of 7-9 Gyr, Solar or sub-Solar [Mg/Fe] ratios, maximum height between 0.5-1.5 kpc, low eccentricities, and a detachment from the expected metallicity gradient with guiding radius. The high metallicity of our stars is incompatible with a formation in the Solar neighbourhood. Their dynamic properties agree with theoretical expectations that these stars travelled from the inner Galaxy due to blurring and, most importantly, to churning. We suggest that most of this population's stars originated in the Milky Way's inner regions (inner disc and/or the bulge) and later migrated to the Solar neighbourhood. The region from where the stars originated had a complex chemical enrichment history, with contributions from supernovae types Ia and II and possibly asymptotic giant branch stars., Comment: 18 pages, 13 figures. Accepted for publication in A&A. Version after language proofs. The catalogue remains to be released. Abridged abstract to fit arxiv's requirements

Aims. In this work, we aim to make a differential comparison of the neutron-capture and p-process element molybdenum (Mo) in the stellar populations in the local disk(s) and the bulge, focusing on minimising possible systematic effects in the analysis. Methods. The stellar sample consists of 45 bulge and 291 local disk K-giants, observed with high-resolution optical spectra. The abundances are determined by fitting synthetic spectra using the SME-code. The disk sample is separated into thin- and thick-disk components using a combination of abundances and kinematics. The cosmic origin of Mo is investigated and discussed by comparing with previous published abundances of Mo and the neutron-capture elements cerium (Ce) and europium (Eu). Results. We determine reliable Mo abundances for 35 bulge and 282 disk giants with a typical uncertainty of [Mo/Fe]~0.2 and ~0.1 dex for the bulge and disk, respectively. Conclusions. We find that the bulge possibly is enhanced in [Mo/Fe] compared to the thick disk, which we do not observe in either [Ce/Fe] nor [Eu/Fe]. This might suggest a higher past star-formation rate in the bulge, however, since we do not observe the bulge to be enhanced in [Eu/Fe], the origin of the molybdenum enhancement is yet to be constrained. Although, the scatter is large, we may be observing evidence of the p-process contributing to the heavy element production in the chemical evolution of the bulge., Comment: Accepted for publication in A&A. 12 pages, 8 figures

We study the evolution of Milky Way thick and thin discs in the light of the most recent observational data. In particular, we analyze abundance gradients of O, N, Fe and Mg along the thin disc as well as the [Mg/Fe] vs. [Fe/H] relations and the metallicity distribution functions at different Galactocentric distances. We run several models starting from the two-infall paradigm, assuming that the thick and thin discs formed by means of two different infall episodes, and we explore several physical parameters, such as radial gas flows, variable efficiency of star formation, different times for the maximum infall onto the disc, different distributions of the total surface mass density of the thick disc and enriched gas infall. Our best model suggests that radial gas flows and variable efficiency of star formation should be acting together with the inside-out mechanism for the thin disc formation. The timescale for maximum infall onto the thin disc, which determines the gap between the formation of the two discs, should be $t_{max}\simeq 3.25$ Gyr. The thick disc should have an exponential, small scale length density profile and gas infall on the inner thin disc should be enriched. We compute also the evolution of Gaia-Enceladus system and study the effects of possible interactions with the thick and thin discs. We conclude that the gas lost by Enceladus or even part of it could have been responsible for the formation of the thick disc but not the thin disc., Comment: 18 pages, 12 figures, 5 tables. Accepted for publication in MNRAS

We extend our previous work on the age-chemical abundance structure of the Galactic outer disc to the inner disc (4 < r < 8 kpc) based on the SDSS/APOGEE survey. Different from the outer disc, the inner disc stars exhibit a clear bimodal distribution in the [Mg/Fe]-[Fe/H] plane. While a number of scenarios have been proposed in the literature, it remains challenging to recover this bimodal distribution with theoretical models. To this end, we present a chemical evolution model embedding a complex multi-phase inner disc formation scenario that matches the observed bimodal [Mg/Fe]-[Fe/H] distribution. In this scenario, the formation of the inner disc is dominated by two main starburst episodes 6 Gyr apart with secular, low-level star formation activity in between. In our model, the first starburst occurs at early cosmic times (t~1 Gyr) and the second one 6 Gyr later at a cosmic time of t~7 Gyr. Both these starburst episodes are associated with gas accretion events in our model, and are quenched rapidly. The first starburst leads to the formation of the high-$\alpha$ sequence, and the second starburst leads to the formation of the metal-poor low-$\alpha$ sequence. The metal-rich low-$\alpha$ stars, instead, form during the secular evolution phase between the two bursts. Our model shows that the $\alpha$-dichotomy originates from the rapid suppression of star formation after the first starburst. The two starburst episodes are likely to be responsible for the formation of the geometric thick disc (z >1 kpc), with the old inner thick disc and the young outer thick disc forming during the first and the second starbursts, respectively., Comment: 16 pages, 10 figures. MNRAS in press

We analyse high resolution spectra of two classical novae that exploded in the Small Magellanic Cloud. $^7$Be II resonance transitions are detected in both ASASSN-19qv and ASASSN-20ni novae. This is the first detection outside the Galaxy and confirms that thermo-nuclear runaway reactions, leading to the $^7$Be formation, are effective also in the low metallicity regime, characteristic of the SMC. Derived yields are of N($^7$Be=$^7$Li)/N(H) = (5.3 $\pm$ 0.2) $\times$ 10$^{-6}$ which are a factor 4 lower than the typical values of the Galaxy. Inspection of two historical novae in the Large Magellanic Cloud observed with IUE in 1991 and 1992 showed also the possible presence of $^7$Be and similar yields. For an ejecta of $M_{H,ej} =$ 10$^{-5}$ M$_{\odot}$, the amount of $^7$Li produced is of $M_{^7 Li} = (3.7 \pm 0.6) \times 10^{-10}$ M$_{\odot}$ per nova event. Detailed chemical evolutionary model for the SMC shows that novae could have made an amount of lithium in the SMC corresponding to a fractional abundance of A(Li) $\approx$ 2.6. Therefore, it is argued that a comparison with the abundance of Li in the SMC, as measured by its interstellar medium, could effectively constrain the amount of the initial abundance of primordial Li, which is currently controversial., 13 pages, 17 figures, 4 tables. Accepted for publication in MNRAS

We test a scenario in which radial migration could affect the Li abundance pattern of dwarf stars in the solar neighbourhood. This may confirm that the Li abundance in these stars can not serve as a probe for the Li abundance in the interstellar medium. We use the high-quality data (including Li abundances) from the 6th internal Data Release of the Gaia-ESO survey. In this sample, we group stars by similarity in chemical abundances via hierarchical clustering. Our analysis treats both measured Li abundances and upper limits. The Li envelope of the previously identified radially migrated stars is well below the benchmark meteoritic value (0 should not be decreased, as recently proposed in the literature. Our study backs the recent studies that claimed that old dwarfs on the hot side of the dip are efficient probes of the ISM abundance of Li, provided atomic diffusion does not lower significantly the initial Li abundance in the atmospheres of metal-rich objects., 8 pages, 3 figures. Abridged abstract to fit ArXiv's requirements. Letter published in A&A Letters. Version after the language proofs

We exploit the unique characteristics of a sample of open clusters (OCs) and field stars for which high-precision 7Li abundances and stellar parameters are homogeneously derived by the Gaia-ESO Survey (GES). We derive possibly undepleted 7Li abundances for 26 OCs and star forming regions with ages from young to old spanning a large range of Galactocentric distances, which allows us to reconstruct the local late Galactic evolution of lithium as well as its current abundance gradient along the disc. Field stars are added to look further back in time and to constrain 7Li evolution in other Galactic components. The data are then compared to theoretical tracks from chemical evolution models that implement different 7Li forges. We find that the upper envelope of the 7Li abundances measured in field stars of nearly solar metallicities traces very well the level of lithium enrichment attained by the ISM as inferred from observations of cluster stars. We confirm previous findings that the abundance of 7Li in the solar neighbourhood does not decrease at supersolar metallicity. The comparison of the data with the chemical evolution model predictions favours a scenario in which the majority of the 7Li abundance in meteorites comes from novae. Current data also seem to suggest that the nova rate flattens out at later times. This requirement might have implications for the masses of the white dwarf nova progenitors and deserves further investigation. Neutrino-induced reactions taking place in core-collapse supernovae also produce some fresh lithium. This likely makes a negligible contribution to the meteoritic abundance, but could be responsible for a mild increase of the 7Li abundance in the ISM of low-metallicity systems that would counterbalance the astration processes., 17 pages, 10 figures, 3 tables (full tables 1 and 3 only available at the CDS), accepted for publication in Astronomy and Astrophysics. Version 2 includes corrections from language editor

[Context] A fundamental element of galaxy formation is the accretion of mass through mergers of satellites or gas. Recent dynamical analyses based on Gaia data have revealed major accretion events in the history of the Milky Way. Nevertheless, our understanding of the primordial Galaxy is hindered because the bona fide identification of the most metal-poor and correspondingly oldest accreted stars remains challenging. [Aims] Galactic archaeology needs a new accretion diagnostic to understand primordial stellar populations. Contrary to α-elements, neutron-capture elements present unexplained large abundance spreads for low-metallicity stars, which could result from a mixture of formation sites. [Methods] We analysed the abundances of yttrium, europium, magnesium, and iron in Milky Way satellite galaxies, field halo stars, and globular clusters. The chemical information was complemented by orbital parameters based on Gaia data. In particular, we considered the average inclination of the orbits. [Results] The [Y/Eu] abundance behaviour with respect to the [Mg/Fe] turnovers for satellite galaxies of various masses reveals that higher-luminosity systems, for which the [Mg/Fe] abundance declines at higher metallicities, present enhanced [Y/Eu] abundances, particularly in the [Fe/H] regime between -2.25 dex and -1.25 dex. In addition, the analysis has uncovered a chemo-dynamical correlation for both globular clusters and field stars of the Galactic halo, accounting for about half of the [Y/Eu] abundance spread. In particular, [Y/Eu] under-abundances typical of protracted chemical evolutions are preferentially observed in polar-like orbits, pointing to a possible anisotropy in the accretion processes. [Conclusions] Our results strongly suggest that the observed [Y/Eu] abundance spread in the Milky Way halo could result from a mixture of systems with different masses. They also highlight that both nature and nurture are relevant to the formation of the Milky Way since its primordial epochs, thereby opening new pathways for chemical diagnostics of the build-up of our Galaxy., Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. ARB, PdL and EFA acknowledge financial support from the ANR 14-CE33-014-01. TA has received funding from the European Union’s Horizon 2020 research and innovation programme under Marie Sklodowska-Curie grant agreement number 745617 and also acknowledges funding from the MINECO (Spanish Ministry of Economy) through grants ESP2016-80079-C2-1-R (MINECO/FEDER, UE) and ESP2014-55996-C2-1-R (MINECO/FEDER, UE). AH acknowledges funding from a Vici grant from the Netherlands Organisation for Scientific Research (NWO).

The analysis of the APOGEE DR16 data suggests the existence of a clear distinction between two sequences of disc stars at different Galactocentric distances in the [$\alpha$/Fe] vs. [Fe/H] abundance ratio space: the so-called high-$\alpha$ sequence, classically associated to an old population of stars in the thick disc, and the low-$\alpha$ sequence, which mostly comprises relatively young stars in the thin disc. We perform a Bayesian analysis based on a Markov Chain Monte Carlo method to constrain a multi-zone two-infall chemical evolution model designed for regions at different Galactocentric distances using measured chemical abundances from the APOGEE DR16 sample. An inside-out formation of the Galaxy disc naturally emerges from the best fit of our two-infall chemical-evolution model to APOGEE-DR16: inner Galactic regions are assembled on shorter time-scales compared to the external ones. In the outer disc (with radii $R>6$ kpc), the chemical dilution due to a late accretion event of gas with primordial chemical composition is the main driver of the [Mg/Fe] vs. [Fe/H] abundance pattern in the low-$\alpha$ sequence. In the inner disc, in the framework of the two-infall model, we confirm the presence of an enriched gas infall in the low-$\alpha$ phase as suggested by chemo-dynamical models. Our Bayesian analysis of the recent APOGEE DR16 data suggests a significant delay time, ranging from $\sim$3.0 to 4.7 Gyr, between the first and second gas infall events for all the analyzed Galactocentric regions. Our results propose a clear interpretation of the [Mg/Fe] vs. [Fe/H] relations along the Galactic discs. The signatures of a delayed gas-rich merger which gives rise to a hiatus in the star formation history of the Galaxy are impressed in the [Mg/Fe] vs. [Fe/H] relation, determining how the low-$\alpha$ stars are distributed in the abundance space at different Galactocentric distances., Comment: Accepted for publication in Astronomy and Astrophysics (A&A), 16 pages, 19 figures

MRK acknowledges support from the Australian Research Council through awards FT180100375 and DP190101258. EW and JTM acknowledge support by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013. SFS is grateful for the support of a CONACYT grant CB-285080 and FC-2016-01-1916, and funding from the PAPIIT-DGAPAIN100519 (UNAM) project.LGwas funded by the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 839090. LG has also been partially supported by the Spanish grant PGC2018-095317-B-C21 within the European Funds for Regional Development (FEDER), In this paper, we analyse the statistics of the 2D gas-phase oxygen abundance distributions of 100 nearby galaxies drawn from the Calar Alto Legacy Integral Field spectroscopy Area survey. After removing the large-scale radial metallicity gradient, we compute the two-point correlation functions of the resulting metallicity fluctuation maps. We detect correlations in the majority of our targets, which we show are significantly in excess of what is expected due to beam-smearing, and are robust against the choice of metallicity diagnostic. We show that the correlation functions are generally well-fit by the predictions of a simple model for stochastic metal injection coupled with diffusion, and from the model we show that, after accounting for the effects of both beam smearing and noise, the galaxies in our sample have characteristic correlation lengths of ∼1 kpc. Correlation lengths increase with both stellar mass and star formation rate, but show no significant variation with Hubble type, barredness, or merging state. We also find no evidence for a theoretically predicted relationship between gas velocity dispersion and correlation length, though this may be due to the small dynamic range in gas velocity dispersion across our sample. Our results suggest that measurements of 2D metallicity correlation functions can be a powerful tool for studying galaxy evolution., Australian Research Council Centre of Excellence CE170100013, H2020 Marie Skłodowska-Curie Actions 839090, PGC2018-095317-B-C21, Australian Research Council DP190101258, FT180100375, Consejo Nacional de Ciencia y Tecnología CB-285080, FC-2016-01-1916, PAPIIT-DGAPAIN100519, Horizon 2020, European Regional Development Fund

We thank the referee for his/her comments and suggestions. SFS and J.B.-B. thanks CONACYT for grants CB-285080 and FC-2016-01-1916, and PAPIIT-DGAPA-IN 100519 (UNAM) project. C.M. thanks UNAM/PAPIIT-IN 101220. J.B.-B. thanks IA-100420 (DGAPA-PAPIIT, UNAM) and CONACYT grant CF19-39578 support. L.G. thanks M.S.-Curie grant 839090. R.G.B. acknowledges support from grants SEV-2017-0709 and P18-FRJ-2595. This study uses data provided by the Calar Alto Legacy Integral Field Area (CALIFA) survey , observed at the Calar Alto Obsevatory., Context. Differential enrichment between alpha and Fe-peak elements is known to be strongly connected with the shape of the star formation history (SFH), the star formation efficiency (SFE), the inflow and outflow of material, and even the shape of the initial mass function (IMF). However, beyond the Local Group, detailed explorations are mostly limited to early-type galaxies due to the lack of a good proxy for [alpha/Fe] in late-type ones, limiting our understanding of the chemical enrichment process. Aims. We intent to extend the explorations of [alpha/Fe] to late-type galaxies in order to understand the details of the differential enrichment process. Methods. We compare the gas-phase oxygen abundance with the luminosity-weighted stellar metallicity in an extensive catalogue of similar to 25 000 H II regions extracted from the Calar Alto Legacy Integral Field Area (CALIFA) survey, an exploration that uses the integral-field spectroscopy of similar to 900 galaxies and covers a wide range of masses and morphologies. This way, we define [O/Fe] as the ratio between both parameters, proposing it as an indirect proxy of the [alpha/Fe] ratio. This procedure is completely different from the one adopted to estimate [alpha/Fe] from high-resolution spectroscopic data for stars in our Galaxy. Results. We illustrate how the [O/Fe] parameter describes the chemical enrichment process in spiral galaxies, finding that: (i) it follows the decreasing pattern with [Fe/H] reported for the [alpha/Fe] ratio and (ii) its absolute scale depends on the stellar mass and the morphology. We reproduce both patterns using two different chemical evolution models, considering that galaxies with different stellar masses and morphologies present either different SFHs, SFEs, and inflow and outflow rates or a different maximum stellar mass cut for the IMF. We will explore the differential chemical enrichment using this new proxy galaxy by galaxy and region by region in further studies., Consejo Nacional de Ciencia y Tecnologia (CONACyT) CB-285080 FC-2016-01-1916 CF19-39578, PAPIIT-DGAPA-IN 100519 101220, M.S.-Curie grant 839090, Programa de Apoyo a Proyectos de Investigacion e Innovacion Tecnologica (PAPIIT), Universidad Nacional Autonoma de Mexico IA-100420 SEV-2017-0709 P18-FRJ-2595

We are grateful for the support of the Consejo Nacional de Ciencia y Tecnolog ' ia (CONACYT) grants CB-285080 and FC-2016-01-1916, and funding from the Universidad Nacional Aut ' onoma de Mexico (UNAM) project PAPIIT-DGAPA-IN100519. LG was funded by the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement no. 839090. This work has been partially supported by the Spanish grant PGC2018-095317-B-C21 within the European Funds for Regional Development (FEDER). We thank P. Tissera, N. Vale-Asari, and J. E. Beckman for their many helpful comments and discussion on the content of the paper., We apply fossil record techniques to the CALIFA sample to study how galaxies in the Local Universe have evolved in terms of their chemical content.We show how the stellar metallicity and the mass–metallicity relation (MZR) evolve through time for the galaxies in our sample and how this evolution varies when we divide them based on their mass, morphology, and star-forming status. We also check the impact of measuring the metallicity at the centre or the outskirts. We find the expected results that the most massive galaxies were enriched more quickly, and that theMZR was steeper at higher redshifts. However, once we separate the galaxies into morphology bins this behaviour is less clear, which suggests that morphology is a primary factor in determining how quickly a galaxy becomes enriched, but with mass determining the final enrichment.We also find that star-forming galaxies (SFGs) appear to be asymptotic in their chemical evolution; that is, the metallicity of SFGs of any mass is very similar at recent times unlike several Gyr ago., Consejo Nacional de Ciencia y Tecnologia (CONACyT) CB-285080 FC-2016-01-1916, Universidad Nacional Autonoma de Mexico PAPIIT-DGAPA-IN100519, European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant 839090, Spanish grant within the European Funds for Regional Development (FEDER) PGC2018-095317-B-C21

J01020100-7122208 is a star whose origin and nature still challenges us. It was first believed to be a yellow super giant ejected from the Small Magellanic Cloud, but it was more recently claimed to be a red giant accelerated by the Milky Way's central black hole. In order to unveil its nature, we analysed photometric, astrometric and high resolution spectroscopic observations to estimate the orbit, age, and 16 elemental abundances. Our results show that this star has a retrograde and highly-eccentric orbit, $e=0.914_{-0.020}^{+0.016}$. Correspondingly, it likely crossed the Galactic disk at $550\;\mathrm{pc}$ from the Galactic centre. We obtained a spectroscopic mass and age of $1.09\pm0.10$ $M_\odot$ and $4.51\pm1.44$ Gyr respectively. Its chemical composition is similar to the abundance of other retrograde halo stars. We found that the star is enriched in europium, having [Eu/Fe] = 0.93 $\pm$ 0.24, and is more metal-poor than reported in the literature, with [Fe/H] = -1.30 $\pm$ 0.10. This information was used to conclude that J01020100-7122208 is likely not a star ejected from the central black of the Milky Way or from the Small Magellanic Cloud. Instead, we propose that it is simply a halo star which was likely accreted by the Milky Way in the distant past but its mass and age suggest it is probably an evolved blue straggler., Comment: 17 pages, 9 Figures, accepted for publication in Monthly Notices of the Royal Astronomical Society

Spina, L., et al. Open clusters are unique tracers of the history of our own Galaxy's disc. According to our membership analysis based on Gaia astrometry, out of the 226 potential clusters falling in the footprint of the GALactic Archaeology with HERMES (GALAH) survey or the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey, we find that 205 have secure members that were observed by at least one of the surveys. Furthermore, members of 134 clusters have high-quality spectroscopic data that we use to determine their chemical composition. We leverage this information to study the chemical distribution throughout the Galactic disc of 21 elements, from C to Eu. The radial metallicity gradient obtained from our analysis is −0.076 ± 0.009 dex kpc, which is in agreement with previous works based on smaller samples. Furthermore, the gradient in the [Fe/H]-guiding radius (r) plane is −0.073 ± 0.008 dex kpc. We show consistently that open clusters trace the distribution of chemical elements throughout the Galactic disc differently than field stars. In particular, at the given radius, open clusters show an age-metallicity relation that has less scatter than field stars. As such scatter is often interpreted as an effect of radial migration, we suggest that these differences are due to the physical selection effect imposed by our Galaxy: clusters that would have migrated significantly also had higher chances to get destroyed. Finally, our results reveal trends in the [X/Fe]-r-age space, which are important to understand production rates of different elements as a function of space and time. LS and AIK acknowledge financial support from the Australian Research Council (Discovery Project 170100521) and from the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013. YST is grateful to be supported by the NASA Hubble Fellowship grant HST-HF2-51425.001 awarded by the Space Telescope Science Institute. TCG acknowledges support from the Spanish Ministry of Science, Innovation and University (MICIU/FEDER, UE) through grant RTI2018-095076-B-C21 and the Institute of Cosmos Sciences University of Barcelona (ICCUB, Unidad de Excelencia María de Maeztu) through grant CEX2019-000918-M. ARC is supported in part by the Australian Research Council through a Discovery Early Career Researcher Award (DE190100656). SLM and DZ acknowledge the support of the Australian Research Council through grant DP180101791. MA is supported by the Australian Research Council (projects FL110100012 and DP150100250). TTG acknowledges financial support from the Australian Research Council through an Australian Laureate Fellowship awarded to JBH.

[Context] Data-driven methods play an increasingly important role in the field of astrophysics In the context of large spectroscopic surveys of stars, data-driven methods are key in deducing physical parameters for millions of spectra in a short time. Convolutional neural networks (CNNs) enable us to connect observables (e.g. spectra, stellar magnitudes) to physical properties (atmospheric parameters, chemical abundances, or labels in general)., [Aims] We test whether it is possible to transfer the labels derived from a high-resolution stellar survey to intermediate-resolution spectra of another survey by using a CNN., [Methods] We trained a CNN, adopting stellar atmospheric parameters and chemical abundances from APOGEE DR16 (resolution R = 22 500) data as training set labels. As input, we used parts of the intermediate-resolution RAVE DR6 spectra (R ∼ 7500) overlapping with the APOGEE DR16 data as well as broad-band ALL_WISE and 2MASS photometry, together with Gaia DR2 photometry and parallaxes., [Results] We derived precise atmospheric parameters Teff, log(g), and [M/H], along with the chemical abundances of [Fe/H], [α/M], [Mg/Fe], [Si/Fe], [Al/Fe], and [Ni/Fe] for 420 165 RAVE spectra. The precision typically amounts to 60 K in Teff, 0.06 in log(g) and 0.02−0.04 dex for individual chemical abundances. Incorporating photometry and astrometry as additional constraints substantially improves the results in terms of the accuracy and precision of the derived labels, as long as we operate in those parts of the parameter space that are well-covered by the training sample. Scientific validation confirms the robustness of the CNN results. We provide a catalogue of CNN-trained atmospheric parameters and abundances along with their uncertainties for 420 165 stars in the RAVE survey., [Conclusions] CNN-based methods provide a powerful way to combine spectroscopic, photometric, and astrometric data without the need to apply any priors in the form of stellar evolutionary models. The developed procedure can extend the scientific output of RAVE spectra beyond DR6 to ongoing and planned surveys such as Gaia RVS, 4MOST, and WEAVE. We call on the community to place a particular collective emphasis and on efforts to create unbiased training samples for such future spectroscopic surveys., Funding for RAVE has been provided by: the Leibniz-Institut für Astrophysik Potsdam (AIP); the Australian Astronomical Observatory; the Australian National University; the Australian Research Council; the French National Research Agency (Programme National Cosmology et Galaxies (PNCG) of CNRS/INSU with INP and IN2P3, co-funded by CEA and CNES); the German Research Foundation (SPP 1177 and SFB 881); the European Research Council (ERC-StG 240271 Galactica); the Istituto Nazionale di Astrofisica at Padova; The Johns Hopkins University; the National Science Foundation of the USA (AST-0908326); the W. M. Keck foundation; the Macquarie University; the Netherlands Research School for Astronomy; the Natural Sciences and Engineering Research Council of Canada; the Slovenian Research Agency (research core funding no. P1-0188); the Swiss National Science Foundation; the Science & Technology Facilities Council of the UK; Opticon; Strasbourg Observatory; and the Universities of Basel, Groningen, Heidelberg, and Sydney. TZ acknowledges financial support of the Slovenian Research Agency (research core funding No. P1-0188) and of the ESA project PHOTO2CHEM (C4000127986). FA is grateful for funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No. 800502. This work has made use of data from the European Space Agency (ESA) mission Gaia (http://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, http://www.cosmos.esa. int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation.

Lithium depletion and enrichment in the cosmos is not yet well understood. To help tighten constraints on stellar and Galactic evolution models, we present the largest high-resolution analysis of Li abundances A(Li) to date, with results for over 100 000 GALAH field stars spanning effective temperatures $5900\,\mathrm{K} \lesssim \rm{T_{eff}} \lesssim7000\,\mathrm{K}$ and metallicities $-3 \lesssim \rm[Fe/H] \lesssim +0.5$. We separated these stars into two groups, on the warm and cool side of the so-called Li-dip, a localised region of the Kiel diagram wherein lithium is severely depleted. We discovered that stars in these two groups show similar trends in the A(Li)-[Fe/H] plane, but with a roughly constant offset in A(Li) of 0.4 dex, the warm group having higher Li abundances. At $\rm[Fe/H]\gtrsim-0.5$, a significant increasing in Li abundance with increasing metallicity is evident in both groups, signalling the onset of significant Galactic production. At lower metallicity, stars in the cool group sit on the Spite plateau, showing a reduced lithium of around 0.4 dex relative to the primordial value predicted from Big Bang nucleosynthesis (BBN). However, stars in the warm group between [Fe/H] = -1.0 and -0.5, form an elevated plateau that is largely consistent with the BBN prediction. This may indicate that these stars in fact preserve the primordial Li produced in the early Universe., 5 pages, 2 figures, Accepted for publication by MNRAS

In this paper, we take advantage of the GAlaxy Evolution and Assembly (GAEA) semi-analytic model to analyse the origin of secondary dependencies in the local galaxy mass - gas metallicity relation. Our model reproduces quite well the trends observed in the local Universe as a function of galaxy star formation rate and different gas-mass phases. We show that the cold gas content (whose largest fraction is represented by the atomic gas phase) can be considered as the third parameter governing the scatter of the predicted mass-metallicity relation, in agreement with the most recent observational measurements. The trends can be explained with fluctuations of the gas accretion rates: a decrease of the gas supply leads to an increase of the gas metallicity due to star formation, while an increase of the available cold gas leads to a metallicity depletion. We demonstrate that the former process is responsible for offsets above the mass-metallicity relation, while the latter is responsible for deviations below the mass-metallicity relation. In low and intermediate mass galaxies, these negative offsets are primarily determined by late gas cooling dominated by material that has been previously ejected due to stellar feedback., Comment: 14 pages, 11 figures + 1 Appendix. Accepted for publication in MNRAS

We investigate the evolution of the abundance of fluorine in the Milky Way thick and thin discs by means of detailed chemical evolution models compared with recent observational data. The chemical evolution models adopted here have already been shown to fit the observed abundance patterns of CNO and $\alpha$-elements as well as the metallicity distribution functions for the Galactic thick and thin disc stars. We apply them here to the study of the origin and evolution of fluorine, which is still a matter of debate. First, we study the importance of the various sites proposed for the production of fluorine. Then, we apply the reference models to follow the evolution of the two different Galactic components. We conclude that rotating massive stars are important producers of F and they can set a plateau in F abundance below [Fe/H]=-0.5 dex, though its existence for [Fe/H], Comment: 8 pages, 2 figures. Accepted for publication in MNRAS

Context. In the era of large spectroscopic surveys, massive databases of high-quality spectra coupled with the products of the Gaia satellite provide tools to outline a new picture of our Galaxy. In this framework, an important piece of information is provided by our ability to infer stellar ages, and consequently to sketch a Galactic timeline. Aims. We aim to provide empirical relations between stellar ages and abundance ratios for a sample of stars with very similar stellar parameters to those of the Sun, namely the so-called solar-like stars. We investigate the dependence on metallicity, and we apply our relations to independent samples, that is, the Gaia-ESO samples of open clusters and of field stars. Methods. We analyse high-resolution and high-signal-to-noise-ratio HARPS spectra of a sample of solar-like stars to obtain precise determinations of their atmospheric parameters and abundances for 25 elements and/or ions belonging to the main nucleosynthesis channels through differential spectral analysis, and of their ages through isochrone fitting. Results. We investigate the relations between stellar ages and several abundance ratios. For the abundance ratios with a steeper dependence on age, we perform multivariate linear regressions, in which we include the dependence on metallicity, [Fe/H]. We apply our best relations to a sample of open clusters located from the inner to the outer regions of the Galactic disc. Using our relations, we are able to recover the literature ages only for clusters located at RGC&Rlarr2; > &Rlarr2; 7 kpc. The values that we obtain for the ages of the inner-disc clusters are much greater than the literature ones. In these clusters, the content of neutron capture elements, such as Y and Zr, is indeed lower than expected from chemical evolution models, and consequently their [Y/Mg] and [Y/Al] are lower than in clusters of the same age located in the solar neighbourhood. With our chemical evolution model and a set of empirical yields, we suggest that a strong dependence on the star formation history and metallicity-dependent stellar yields of s-process elements can substantially modify the slope of the [s/α]-[Fe/H]-age relation in different regions of the Galaxy. Conclusions. Our results point towards a non-universal relation [s/α]-[Fe/H]-age, indicating the existence of relations with different slopes and intercepts at different Galactocentric distances or for different star formation histories. Therefore, relations between ages and abundance ratios obtained from samples of stars located in a limited region of the Galaxy cannot be translated into general relations valid for the whole disc. A better understanding of the s-process at high metallicity is necessary to fully understand the origin of these variations. © ESO 2020., The authors would like to thanks Dr. Leslie K. Hunt for her help in the statistical interpretation of our results. Based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 188.B-3002. These data products have been processed by the Cambridge Astronomy Survey Unit (CASU) at the Institute of Astronomy, University of Cambridge, and by the FLAMES/UVES reduction team at INAF/Osservatorio Astrofisico di Arcetri. These data have been obtained from the GES Survey Data Archive, prepared and hosted by the Wide Field Astronomy Unit, Institute for Astronomy, University of Edinburgh, which is funded by the UK Science and Technology Facilities Council (STFC). This research has made use of the services of the ESO Science Archive Facility. This work was partly supported by the European Union FP7 programme through ERC grant number 320360 and by the Leverhulme Trust through grant RPG-2012-541. We acknowledge the support from INAF and Ministero dell' Istruzione, dell' Universita e della Ricerca (MIUR) in the form of the grant "Premiale VLT 2012". The results presented here benefit from discussions held during the GES workshops and conferences supported by the ESF (European Science Foundation) through the GREAT Research Network Programme. LM acknowledge the funding from the INAF PRIN-SKA 2017 program 1.05.01.88.04. LM and MVdS acknowledge the funding from MIUR Premiale 2016: MITIC. T.B. was supported by the project grant "The New Milky Way" from the Knut and Alice Wallenberg Foundation. M. acknowledges support provided by the Spanish Ministry of Economy and Competitiveness (MINECO), under grant AYA-2017-88254-P. L.S. acknowledges financial support from the Australian Research Council (Discovery Project 170100521) and from the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013. F.J.E. acknowledges financial support from the ASTERICS project (ID:653477, H2020-EU.1.4.1.1. - Developing new world-class research infrastructures). U.H. acknowledges support from the Swedish National Space Agency (SNSA/Rymdstyrelsen). T.B was partly funded by the project grant "The New Milky Way" from the Knut and Alice Wallenberg Foundation, and partly by grant No. 2018-04857 from the Swedish Research Council.

Context. The vast majority of the known stars of ultra low metallicity ([Fe=H] >-4:5) are known to be enhanced in carbon, and belong to the 'low-carbon band' (A(C) = log(C=H) + 12 7:6). It is generally, although not universally, accepted that this peculiar chemical composition reflects the chemical composition of the gas cloud out of which these stars were formed. The first ultra-metalpoor star discovered, HE 0107-5240, is also enhanced in carbon and belongs to the 'low-carbon band'. It has recently been claimed to be a long-period binary, based on radial velocity measurements. It has also been claimed that this binarity may explain its peculiar composition as being due to mass transfer from a former AGB companion. Theoretically, low-mass ratios in binary systems are much more favoured amongst Pop III stars than they are amongst solar-metallicity stars. Any constraint on the mass ratio of a system of such low metallicity would shed light on the star formation mechanisms in this metallicity regime. Aims.We acquired one high precision spectrum withESPRESSO in order to check the reality of the radial velocity variations. In addition we analysed all the spectra of this star in the ESO archive obtained with UVES to have a set of homogenously measured radial velocities. Methods. The radial velocities were measured using cross correlation against a synthetic spectrum template. Due to the weakness of metallic lines in this star, the signal comes only from the CH molecular lines of the G-band. Results. The measurement obtained in 2018 from an ESPRESSO spectrum demonstrates unambiguously that the radial velocity of HE 0107-5240 has increased from 2001 to 2018. Closer inspection of the measurements based on UVES spectra in the interval 2001-2006 show that there is a 96% probability that the radial velocity correlates with time, hence the radial velocity variations can already be suspected from the UVES spectra alone. Conclusions.We confirm the earlier claims of radial velocity variations in HE0107-5240. The simplest explanation of such variations is that the star is indeed in a binary system with a long period. The nature of the companion is unconstrained and we consider it is equally probable that it is an unevolved companion or a white dwarf. Continued monitoring of the radial velocities of this star is strongly encouraged., With funding from the Spanish government through the "María de Maeztu Unit of Excellence" accreditation (MDM-2017-0737)

We investigate the discrepancy between oxygen abundance estimations for narrow-line regions of active galactic nuclei (AGNs) type Seyfert 2 derived using direct estimations of the electron temperature (T-e-method) and those derived using photoionization models. In view of this, observational emission-line ratios in the optical range (3000 < lambda(angstrom) < 7000) of Seyfert 2 nuclei compiled from the literature were reproduced by detailed photoionization models built with the CLOUDY code. We find that the derived discrepancies are mainly due to the inappropriate use of the relations between temperatures of the low (t(2)) and high (t(3)) ionization gas zones derived for H II regions in AGN chemical abundance studies. Using a photoionization model grid, we derived a new expression for t(2) as a function of t(3) valid for Seyfert 2 nuclei. The use of this new expression in the AGN estimation of the O/H abundances based on Te-method produces O/H abundances slightly lower (about 0.2 dex) than those derived from detailed photoionization models. We also find that the new formalism for the T-e-method reduces by about 0.4 dex the O/H discrepancies between the abundances obtained from strong emission-line calibrations and those derived from direct estimations. © 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society, OLD and ACK are grateful to Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) and Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPQ). MA is grateful to Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES). MVC and GFH are grateful to CONICET. OLD thanks the kindly hospitality of the Kavli Institute for Cosmology staff where part of thisworkwas developed. RMacknowledges ERC Advanced Grant 695671 'QUENCH` and support by the Science and Technology Facilities Council (STFC).

The orbits of the least chemically enriched stars open a window on the formation of our Galaxy when it was still in its infancy. The common picture is that these low-metallicity stars are distributed as an isotropic, pressure-supported component since these stars were either accreted from the early building blocks of the assembling Milky Way, or were later brought by the accretion of faint dwarf galaxies. Combining the metallicities and radial velocities from the Pristine and LAMOST surveys and Gaia DR2 parallaxes and proper motions for an unprecedented large and unbiased sample of very metal-poor stars at $[Fe/H]\leq-2.5$ we show that this picture is incomplete. This sample shows strong statistical evidence (at the $5.0\sigma$ level) of asymmetry in their kinematics, favouring prograde motion. Moreover, we find that $31\%$ of the stars that currently reside in the disk do not venture outside of the disk plane throughout their orbit. The discovery of this population implies that a significant fraction of stars with iron abundances $[Fe/H]\leq-2.5$ formed within or concurrently with the Milky Way disk and that the history of the disk was quiet enough to allow them to retain their disk-like orbital properties., Comment: Submitted to MNRAS letter, 5 pages with 1 figure. Appendices A and B with 3 figures

The metal-rich Galactic globular cluster NGC 6366 is the fifth closest to the Sun. Despite its interest, it has received scarce attention, and little is known about its internal structure. Its kinematics suggests a link to the halo, but its metallicity indicates otherwise. We present a detailed chemical analysis of eight giant stars of NGC 6366, using high resolution and high quality spectra (R > 40000, S/N > 60) obtained at the VLT (8.2 m) and CFHT (3.6 m) telescopes. We attempted to characterize its chemistry and to search for evidence of multiple stellar populations. The atmospheric parameters were derived using the method of excitation and ionization equilibrium of FeI and FeII lines and from those atmospheric parameters we calculated the abundances for other elements and found that none of the elements measured presents star-to-star variation greater than the uncertainties. We compared the derived abundances with those of other globular clusters and field stars available in the literature. We determined a mean [Fe/H] = -0.60 +- 0.03 for NGC 6366 and found some similarity of this object with M 71, another inner halo globular cluster. The Na-O anticorrelation extension is short and no star-to-star variation in Al is found. The presence of second generation stars is not evident in NGC 6366., 17 pages, 14 figures. Accepted for publication in MNRAS; Corrected typos and added references

Iron suffers from high levels of depletion in the highly ionized environments of planetary nebulae, making the direct determination of undepleted elemental iron abundances difficult. Zinc, which does not suffer from the same depletion effects as iron, may be used as a surrogate element to measure iron abundances as there is an approximately constant zinc-to-iron ratio across a wide range of metallicities. In this paper, we report zinc abundances of six Galactic Bulge planetary nebulae determined from new observations taken with ISAAC on the Very Large Telescope, Chile, prior to the instrument's decommissioning as well as a further three based upon literature observations. UVES data of the sample planetary nebulae are presented and have been used to derive abundances, temperatures and densities of a variety of elements and ions. The abundances derived from the UVES data agree well with results from the literature. [Zn/H], determined from the ISAAC observations, is found to be generally sub-solar and [O/Zn] is found to be either consistent or enriched with respect to Solar., 13 pages, accepted for publication in MNRAS

In the era of large high-resolution spectroscopic surveys, high-quality spectra can contribute to our understanding of the Galactic chemical evolution, providing chemical abundances belonging to the different nucleosynthesis channels, and also providing constraints to stellar age. Some abundance ratios have been proven to be excellent indicators of stellar ages. We aim at providing an empirical relationship between stellar ages and [C/N] using, as calibrators, open star clusters observed by both the Gaia-ESO and APOGEE surveys. We use stellar parameters and abundances from the Gaia-ESO and APOGEE of the Galactic field and open cluster stars. Ages of star clusters are retrieved from the literature sources and validated using a common set of isochrones. We use the same isochrones to determine, for each age and metallicity, the surface gravity at which the first dredge-up and red giant branch bump occur. We study the effect of extra-mixing processes in our sample of giant stars, and we derive the mean [C/N] in evolved stars, including only stars without evidence of extra-mixing. Combining the Gaia-ESO and APOGEE samples of open clusters, we derive a linear relationship between [C/N] and logarithmic cluster ages. We apply our relationship to selected giant field stars in both Gaia-ESO and APOGEE. We find an age separation between thin and thick disc stars and age trends within their populations, with an increasing age towards lower metallicity populations. With such empirical relationship, we are able to provide an age estimate for giant stars in which C and N abundances are measured. Isochrone fitting is less sensitive for giant than dwarf stars at the turn off. The present method can be thus considered as an additional tool to give an independent estimate of the age of giant stars, with uncertainties in their ages comparable to those obtained using isochrone fitting for dwarf stars., Comment: 28 pages, 24 figures. Accepted by A&A

Simpson's paradox, or Yule-Simpson effect, arises when a trend appears in different subsets of data but disappears or reverses when these subsets are combined. We describe here seven cases of this phenomenon for chemo-kinematical relations believed to constrain the Milky Way disk formation and evolution. We show that interpreting trends in relations, such as the radial and vertical chemical abundance gradients, the age-metallicity relation, and the metallicity-rotational velocity relation (MVR), can lead to conflicting conclusions about the Galaxy past if analyses marginalize over stellar age and/or birth radius. It is demonstrated that the MVR in RAVE giants is consistent with being always strongly negative, when narrow bins of [Mg/Fe] are considered. This is directly related to the negative radial metallicity gradients of stars grouped by common age (mono-age populations) due to the inside out disk formation. The effect of the asymmetric drift can then give rise to a positive MVR trend in high-[alpha/Fe] stars, with a slope dependent on a given survey's selection function and observational uncertainties. We also study the variation of lithium abundance, A(Li), with [Fe/H] of AMBRE:HARPS dwarfs. A strong reversal in the positive A(Li)-[Fe/H] trend of the total sample is found for mono-age populations, flattening for younger groups of stars. Dissecting by birth radius shows strengthening in the positive A(Li)-[Fe/H] trend, shifting to higher [Fe/H] with decreasing birth radius; these observational results suggest new constraints on chemical evolution models. This work highlights the necessity for precise age estimates for large stellar samples covering wide spatial regions., 13 p., 7 Fig., Accepted to MNRAS

Precise stellar ages from asteroseismology have become available and can help setting stronger constraints on the evolution of the Galactic disc components. Recently, asteroseismology has confirmed a clear age difference in the solar annulus between two distinct sequences in the [$\alpha$/Fe] versus [Fe/H] abundance ratios relation: the high-$\alpha$ and low-$\alpha$ stellar populations. We aim at reproducing these new data with chemical evolution models including different assumptions for the history and number of accretion events. We tested two different approaches: a revised version of the `two-infall' model where the high-$\alpha$ phase forms by a fast gas accretion episode and the low-$\alpha$ sequence follows later from a slower gas infall rate, and the parallel formation scenario where the two disc sequences form coevally and independently. The revised `two-infall' model including uncertainties in age and metallicity is capable of reproducing: i) the [$\alpha$/Fe] vs. [Fe/H] abundance relation at different Galactic epochs, ii) the age$-$metallicity relation and the time evolution [$\alpha$/Fe]; iii) the age distribution of the high-$\alpha$ and low-$\alpha$ stellar populations, iv) the metallicity distribution function. The parallel approach is not capable of properly reproduce the stellar age distribution, in particular at old ages. In conclusion, the best chemical evolution model is the revised `two-infall' one, where a consistent delay of $\sim$4.3 Gyr in the beginning of the second gas accretion episode is a crucial assumption to reproduce stellar abundances and ages., Comment: Accepted for publication in A&A; 20 pages, 20 figures

The stellar initial mass function (IMF) regulates the baryonic cycle within galaxies, and is a key ingredient to translate observations into physical quantities. Although for decades it was assumed to be universal, there is now growing observational evidence showing that the center of massive early-type galaxies host an enhanced population of low-mass stars compared to the expectations from the Milky Way. Moreover, these variations in the IMF have been found to be related to the radial metallicity variations in massive galaxies. We present here a two-dimensional stellar population analysis of the massive lenticular galaxy FCC 167 (NGC 1380) as part of the Fornax3D project. Using a newly developed stellar population fitting scheme, we derive a full two-dimensional IMF map of an early-type galaxy. This two-dimensional analysis allows us go further than a radial analysis, showing how the metallicity changes along a disc-like structure while the IMF follows a distinct, less disky distribution. Thus, our findings indicate that metallicity cannot be the sole driver of the observed radial IMF variations. In addition, a comparison with the orbital decomposition shows suggestive evidence of a coupling between stellar population properties and the internal dynamical structure of FCC 167, where metallicity and IMF maps seem to track the distribution of cold and warm orbits, respectively., Comment: 12 pages, 7 figures. Accepted for publication in Astronomy & Astrophysics

We have performed a detailed spectral analysis of the inner halo Galactic globular cluster (GC) NGC 6723 using high resolution (R$\approx$ 22000-48000) spectra for for eleven red giant branch stars collected with MIKE (Magellan) and FEROS (MPG/ESO). This globular is located at the minimum of the bimodal metallicity distribution of GCs suggesting that it might be an excellent transitional system between metal-intermediate and metal-rich GCs. In spite of its metal-intermediate status, it is characterized by an extended horizontal branch and by a large number of RR Lyrae stars. We investigated abundances of a variety of species including light, $\alpha$-, Fe-peak, and neutron capture elements. We found a mean metallicity $[Fe/H]=-0.93 \pm 0.05$ dex, and a typical $\alpha$ -enrichment ($[\alpha/Fe] \approx 0.39$) that follows the trend of metal-poor and metal-intermediate GCs. The same outcome applies for light metals (Na, Al), Fe-peak (V, Cr, Mn, Fe, Co, Ni, Cu), $s$/$r$-process elements (Ba, Eu) and for the classical anti-correlation: Na-O and Mg-Al. The current findings further support the evidence that the chemical enrichment of NGC 6723 is in more line with metal-intermediate GCs and their lower metallicity counterparts, and it does not bring forward the prodrome of the metal-rich regime., Comment: MNRAS, accepted for publication

Neutron star mergers (NSM) are likely to be the main production sites for the rapid (r-) neutron capture process elements. We study the r-process enrichment of the stellar halo of the Milky Way through NSM, by tracing the typical r-process element Eu in the Munich-Groningen semi-analytic galaxy formation model, applied to three high resolution Aquarius dark matter simulations. In particular, we investigate the effect of the kick velocities that neutron star binaries receive upon their formation, in the building block galaxies (BBs) that partly formed the stellar halo by merging with our Galaxy. When this kick is large enough to overcome the escape velocity of the BB, the NSM takes place outside the BB with the consequence that there is no r-process enrichment. We find that a standard distribution of NS kick velocities decreases [Eu/Mg] abundances of halo stars by $\sim 0.5$~dex compared to models where NS do not receive a kick. With low NS kick velocities, our simulations match observed [Eu/Mg] abundances of halo stars reasonably well, for stars with metallicities [Mg/H]$\geq -1.5$. Only in Aquarius halo B-2 also the lower metallicity stars have [Eu/Mg] values similar to observations. We conclude that our assumption of instantaneous mixing is most likely inaccurate for modelling the r-process enrichment of the Galactic halo, or an additional production site for r-process elements is necessary to explain the presence of low-metallicity halo stars with high Eu abundances., Comment: 15 pages, 9 figures, accepted for publication in MNRAS

Detailed chemical abundances of Galactic stars are needed in order to improve our knowledge of the formation and evolution of our galaxy, the Milky Way. We took advantage of the GIANO archive spectra to select a sample of Galactic disc stars in order to derive their chemical inventory and to compare the abundances we derived from these infrared spectra to the chemical pattern derived from optical spectra. We analysed high-quality spectra of 40 stars observed with GIANO. We derived the stellar parameters from the photometry and the Gaia data-release 2 (DR2) parallax; the chemical abundances were derived with the code MyGIsFOS. For a subsample of stars we compared the chemical pattern derived from the GIANO spectra with the abundances derived from optical spectra. We derived P abundances for all 40 stars, increasing the number of Galactic stars for which phosphorus abundance is known. We could derive abundances of 14 elements, 8 of which are also derived from optical spectra. The comparison of the abundances derived from infrared and optical spectra is very good. The chemical pattern of these stars is the one expected for Galactic disc stars and is in agreement with the results from the literature. GIANO is providing the astronomical community with an extremely useful instrument, able to produce spectra with high resolution and a wide wavelength range in the infrared., A&A in press

With the wealth of information from large surveys and observational campaigns in the contemporary era, it is critical to properly exploit the data to constrain the parameters of Galactic chemical evolution models and quantify the associated uncertainties. We aim at constraining the two-infall chemical evolution models for the solar annulus using the measured chemical abundance ratios and seismically inferred age of stars in the APOKASC sample. In the revised two-infall chemical evolution models by Spitoni et al. (2019), a significant delay of $\sim 4.3$ Gyr has been invoked between the two episodes of gas accretion. In this work, we wish to test its robustness and statistically confirm/quantify the delay. For the first time, a Bayesian framework based on Markov Chain Monte Carlo methods has been used for fitting the two-infall chemical evolution models to the data. In addition to fitting the data for stars in the APOKASC sample, our best fit models also reproduce other important observational constraints of the chemical evolution of the disk: i) present day stellar surface density; ii) present day supernova and star formation rates; iii) the metallicity distribution function; and iv) solar abundance values. We found a significant delay between the two gas accretion episodes for various models explored with different values for the star formation efficiencies. The values for the delay lie in the range $4.5-5.5$ Gyr. The results suggest that the APOKASC sample carries the signature of delayed gas-rich merger, with the dilution as main process determining the shape of low-$\alpha$ stars in the abundance ratios space., Comment: Accepted for publication in Astronomy and Astrophysics (A&A), 12 pages, 13 figures

We study a sample of 17 z>1.5 absorbers selected based on the presence of strong CI absorption lines in SDSS spectra and observed with the ESO-VLT spectrograph X-shooter. We derive metallicities, depletion onto dust, and extinction by dust, and analyse the absorption from MgII, MgI, CaII and NaI that are redshifted into the near infrared wavelength range. We show that most of these CI absorbers have high metallicity and dust content. We detect nine CaII absorptions with $W$(CaII$\lambda$3934) >0.23 \AA out of 14 systems where we have appropriate wavelength coverage. The observed equivalent widths are similar to what has been measured in other lower redshift surveys of CaII systems. We detect ten NaI absorptions in the 11 systems where we could observe this absorption. The median equivalent width ($W$(NaI$\lambda$5891) = 0.68 \AA) is larger than what is observed in local clouds with similar HI column densities but also in z 2.5 \AA and six of them have log N(HI) < 20.3, with the extreme case of J1341+1852 that has log N(HI) = 18.18. The MgII absorptions are spread over more than $\Delta v$ $\sim$ 400 km s$^{-1}$ for half of the systems; three absorbers have $\Delta v$ > 500 km s$^{-1}$. The kinematics are strongly perturbed for most of these systems, which probably do not arise in quiet disks and must be close to regions with intense star-formation activity and/or are part of interacting objects. All this suggests that a large fraction of the cold gas at high redshift arises in disturbed environments., Comment: 26 pages, 49 figures, 3 tables, accepted by Astronomy & Astrophysics (A&A)

IC 166 is an intermediate-age open cluster ($\sim 1$ Gyr) which lies in the transition zone of the metallicity gradient in the outer disc. Its location, combined with our very limited knowledge of its salient features, make it an interesting object of study. We present the first high-resolution spectroscopic and precise kinematical analysis of IC 166, which lies in the outer disc with $R_{GC} \sim 12.7$ kpc. High resolution \textit{H}-band spectra were analyzed using observations from the SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. We made use of the Brussels Automatic Stellar Parameter (BACCHUS) code to provide chemical abundances based on a line-by-line approach for up to eight chemical elements (Mg, Si, Ca, Ti, Al, K, Mn and Fe). The $\alpha-$element (Mg, Si, Ca and whenever available Ti) abundances, and their trends with Fe abundances have been analysed for a total of 13 high-likelihood cluster members. No significant abundance scatter was found in any of the chemical species studied. Combining the positional, heliocentric distance, and kinematic information we derive, for the first time, the probable orbit of IC 166 within a Galactic model including a rotating boxy bar, and found that it is likely that IC 166 formed in the Galactic disc, supporting its nature as an unremarkable Galactic open cluster with an orbit bound to the Galactic plane., Comment: 16 pages, 7 tables, 8 figures, accepted for publication in AJ

Investigating the chemical homogeneity of stars born from the same molecular cloud at virtually the same time is very important for our understanding of the chemical enrichment of the interstellar medium and with it the chemical evolution of the Galaxy. One major cause of inhomogeneities in the abundances of open clusters is stellar evolution of the cluster members. In this work, we investigate variations in the surface chemical composition of member stars of the old open clusterM67 as a possible consequence of atomic diffusion effects taking place during the main-sequence phase. The abundances used are obtained from high-resolution UVES/FLAMES spectra within the framework of the Gaia-ESO Survey. We find that the surface abundances of stars on the main sequence decrease with increasing mass reaching a minimum at the turn-off. After deepening of the convective envelope in subgiant branch stars, the initial surface abundances are restored.We found themeasured abundances to be consistent with the predictions of stellar evolutionary models for a cluster with the age and metallicity of M67. Our findings indicate that atomic diffusion poses a non-negligible constraint on the achievable precision of chemical tagging methods.© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society., This work was supported by Sonderforschungsbereich SFB 881 'The Milky Way System' (subproject B5) of the German Research Foundation (DFG). AB acknowledges support from the SFB 881 visitor program. CBM thanks Elisabetta Caffau for fruitful discussions and Don VandenBerg for providing the isochrones shown in Fig 1. The authors would like to thank the anonymous referee for the constructive comments that helped in improving the present work.r MTC acknowledges the financial support from the Spanish Ministerio de Economia y Competitividad, through grant AYA2016-75931. AD and GT acknowledge support by the Research Council of Lithuania (MIP-082/2015). UH acknowledges support from the Swedish National Space Board (SNSB/Rymdstyrelsen). TB was supported by the project grant 'The New Milky' from the Knut and Alice Wallenberg foundation. RS acknowledges support from the Polish Ministry of Science and Higher Education. SGS and VA acknowledge the support by Fundacao para a Ciencia e Tecnologia (FCT) through national funds and a research grant (project ref. UID/FIS/04434/2013, and PTDC/FISAST/7073/2014). SGS also acknowledges the support from FCT through Investigador FCT contract of reference IF/00028/2014 and POPH/FSE (EC) by FEDER funding through the program 'Programa Operacional de Factores de Competitividade - COMPETE'. VA acknowledges the support from FCT through Investigador FCT contract IF/00650/2015/CP1273/CT0001. EJA acknowledges partial support from the Spanish Ministry for Economy and Competitiveness and FEDER funds through grant AYA2013-40611-P. ARC is supported through an Australian Research Council Discovery Project under grant DP160100637. CL thanks the Swiss National Science Foundation for supporting this research through the Ambizione grant number PZ00P2 168065. AK acknowledges support from the Swedish National Space Board (SNSB). XF acknowledges financial support from Premiale 2015 MITiC (PI B/Garilli). SLM acknowledges support from the Australian Research Council through grant DE140100598. AB acknowledges support from the Millennium Science Initiative (Chilean Ministry of Economy).r Based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 188.B-3002. These data products have been processed by the Cambridge Astronomy Survey Unit (CASU) at the Institute of Astronomy, University of Cambridge, and by the FLAMES/UVES reduction team at INAF/Osservatorio Astrofisico di Arcetri. These data have been obtained from the Gaia-ESO Survey Data Archive, prepared and hosted by the Wide Field Astronomy Unit, Institute for Astronomy, University of Edinburgh, which is funded by the UK Science and Technology Facilities Council. This work was partly supported by the European Union FP7 programme through ERC grant number 320360 and by the Leverhulme Trust through grant RPG-2012-541. We acknowledge the support from INAF and Ministero dell' Istruzione, dell' Universita' e della Ricerca (MIUR) in the form of the grant 'Premiale VLT 2012', and through PRIN-INAF 2014 'The Gaia-ESO Survey'. The results presented here benefit from discussions held during the Gaia-ESO workshops and conferences supported by the ESF (European Science Foundation) through the GREAT Research Network Programme. This research has made use of the SIMBAD data base, operated at CDS, Strasbourg, France and NASA's Astrophysics Data System.