arXiv subjects

A. Mucciarelli

Publications and source records attributed to A. Mucciarelli.

At least 19 recordsLinked to original sources

arXiv2026

X-shooter spectroscopy of giant stars in the nuclear star cluster

Near-IR spectra of a homogeneous sample of 15 red giants in the Galactic nuclear star cluster, within 1.5 pc of SgrA*, have been acquired with X-shooter at the Very Large Telescope. From these spectra line-of-sight radial velocities and chemical abundances of iron, carbon, oxygen and other alpha and light elements have been derived. By combining radial velocities from this study and proper motions from the literature we computed the orbits of these stars, finding that they have been confined within 12 pc from SgrA* for their entire lifetime, thus strongly suggesting an in-situ formation and evolution. Iron abundances between half and twice solar, about solar-scaled values within +/-0.1 dex for {\alpha} elements, Ti and V, some enhancement of [Na/Fe], [K/Fe] and [Al/Fe] and some depletion of [C/Fe] with respect to the solar ratios have been measured. The inferred chemical abundance distributions are consistent with a formation from a gas enriched by both type II and type I SNe over a prolonged timescale, closely matching those of the metal-rich populations of the inner bulge field and other complex stellar systems like Terzan 5 and Liller 1.

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arXiv2026

The Hubble Missing Globular Clusters Survey IV. Ultra-faint compact satellites of the Milky Way. The case of Koposov 2

In the last decades a number of extremely faint and compact Galactic satellites (Ultra Faint Compact Satellites; UFCS) have been discovered by large panoramic surveys. Their nature is uncertain due to their location in the overlapping dwarf galaxy-star cluster region of the $M_V-R_h$ plane and their faintness and distance. Here we show how the deep HST photometry from the Missing Globular Clusters Survey (MGCS), combined with spectroscopic metallicities, provides new insight into the nature of these satellites through accurate distance and age estimates. We consider the case of Koposov 2, currently the most metal-poor bound star cluster known in the Milky Way or an extreme case of Ultra Faint Dwarf galaxy. By performing a spectroscopically-informed bayesian isochrone fit on the MGCS data we find $(m-M)_0=16.85\pm0.06$ ($D=23.4\pm0.6$ kpc) and age=$13.7^{+0.9}_{-1.3}$ Gyr, showing that, contrary to previous age estimates, Koposov 2 is as old as the oldest Galactic globular clusters. The luminosity function, corrected for incompleteness, is well reproduced by a model with the same age and metallicity and a slope of the mass function $x=-0.35$, suggesting a significant depletion of faint stars. We model the surface stellar density field, deriving new robust estimates of the half-light radius ($R_h=0.39^{+0.06}_{-0.04}$ arcsec, corresponding to $R_h=2.7^{+0.4}_{-0.3}$ pc), of the absolute integrated magnitude ($M_V=-0.95\pm0.22$) and of the stellar mass $M_\star=371.8\pm41.6M_{\odot}$), showing that Koposov 2 is much more compact than confirmed dwarf galaxies of similar stellar mass. The new evidence significantly support the hypothesis that Koposov 2 is a star cluster that may have lost a large fraction of its mass. Finally we show that most UFCS lie in the same locus of the $M_\star-R_h$ plane as Galactic open clusters, hinting to a possible additional channel for their formation.

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arXiv2026

TYC 170-1218-1: A new r-process-enhanced extremely metal-poor star, rich in Th

Context . Extremely metal-poor (EMP) stars are formed from gas clouds enriched by one or a few supernova explosions belonging to the first stellar generation and this very limited number of sources of metal enrichment is suitable to produce peculiar chemical patterns that give birth to stars with anomalous chemical composition. Among the EMP stars, r-II stars are characterised by an over-abundance of the heavy elements with respect to iron. Aims . In the search for apparently young, metal-poor stars, we serendipitously selected TYC 170-1218-1, which turned out to be an EMP star, enhanced in neutron capture elements over iron. Our aim is to obtain a detailed chemical inventory for this exceptional object. Methods . We investigated high-resolution spectra observed with UVES at the VLT telescope and Mike at the Magellan Clay telescope. We derived the abundance of 33 elements using the MyGIsFOS code and an ATLAS 9 model atmosphere. Results . The star is an EMP with [Fe/H] = -3.52. It is enhanced in the $\alpha$ elements, as EMP stars usually are. It is an r-II star with [Eu/Fe] = +1.84 and [Th/Fe] = +1.85. The star is also poor in carbon with respect to iron. The quality of the spectra was insufficient for us to detect uranium. Kinematically the star belongs now to the Galactic halo, but it joined the Milky Way during the Sequoia accretion event.

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arXiv2026

The Hubble Missing Globular Cluster Survey. III. Astro-photometric catalogs, artificial-star tests, and improved absolute proper motions

The Hubble Missing Globular Cluster Survey (MGCS) has taken one of the last opportunities to complete the census of Galactic globular clusters (GCs) started by past Hubble Space Telescope (HST) programs, securing high-resolution data for 34 GCs never observed before by HST. The previous papers in the series have highlighted the astrometric and photometric potential of the project by analyzing a subsample of targets. We present, and release to the community, the official astro-photometric catalogs of the MGCS for all GCs imaged by this project. We describe the data reduction using state-of-the-art techniques designed for HST. We discuss the photometric calibration and show, for the first time, the synergy with the Gaia catalog to ensure homogeneous photometry across our data set. We compute artificial-star tests that can be used to assess systematics and the completeness level of our data. We combined HST and Gaia data to refine the absolute proper motions of our GCs, reaching a precision $\sim$3 times better than that of Gaia alone. We used these new proper motions to update (and to determine for the first time for five systems) the associations between GCs and their putative galaxy progenitors. This work continues decades-long efforts of large Treasury programs in sharing precise and accurate atlases to the community for studying GCs across a wide range of scientific endeavors.

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arXiv2026

Low-resolution spectroscopic characterisation of five poorly known Galactic stellar clusters

Stellar clusters preserve crucial information on the formation and evolutionary processes that shaped the Milky Way (MW) as we see it today. However, several MW clusters still lack sufficient data to constrain their metallicity, ages, and, in some cases, even their basic kinematic properties. We present low-resolution MODS at LBT spectroscopy for five such systems (i.e. Koposov 1, Koposov 2, Mu\~noz 1, Pfleiderer 2, and RLGC2) from which we derive systemic heliocentric radial velocities ($V_{\rm sys}$) with typical uncertainties of $\le 10$ km/s, and metallicities based on the equivalent widths of the infrared Ca II triplet measured in red giant branch members. For Pfleiderer 2 and RLGC2, we provide the first spectroscopic determinations of their systemic velocities and metallicities, finding $V_{\rm sys}= 6 \pm 5$ km/s and $-313 \pm 6$ km/s, and $\mathrm{[Fe/H]}= -0.75 \pm 0.09$ dex and $-2.33 \pm 0.13$ dex, respectively. For the other three clusters, we find results that are consistent with the existing literature. Thanks to our new spectroscopic measurements, we were able to perform an orbital analysis to investigate their origin. We find that Pfleiderer 2 likely formed within the MW, RLGC2 is dynamically associated to the Gaia-Sausage-Enceladus accretion event, and Koposov 1 was likely stripped from the Sagittarius dwarf spheroidal while Mu\~noz 1 is only tentatively associated with the latter system. In the end, Koposov 2 at high orbital energy does not show a clear association with any known progenitor system.

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arXiv2026

MgAl burning chain in M 54: the globular cluster-like properties of a nuclear star cluster

In this study, we present the chemical abundances of Fe, Mg, Al, Si, and K for a sample of 233 likely member stars of M 54. All the stars were observed with the FLAMES high-resolution multi-object spectrograph mounted at the VLT. Our analysis confirmed the presence of a large metallicity range in M 54, with the majority of the stars having -1.8 < [Fe/H] < -1.0 dex and few stars with [Fe/H] > -1.0 dex. The mean value of the total sample is [Fe/H] = -1.40 ({\sigma} = 0.22 dex). A Markov Chain Monte Carlo analysis revealed that the observed spread in [Fe/H] is compatible with a non-null intrinsic iron dispersion. We also found that the metallicity distribution function and the broadening of the red giant branch of M 54 are not compatible with a single age, but instead they suggest a wide age range from ~ 13 Gyr to ~ 1 - 2 Gyr or a smaller age range if a significant He enhancement (Y ~ 0.35/0.40) is present in the most metal-rich stars. We identified among the stars in M 54 the entire pattern of anticorrelations linked to the MgAl burning cycle. In particular, the metal-rich component displays a higher level of H-burning with the presence of more extended anticorrelations than the metal-poor component. No Mg-poor ([Mg/Fe]<0.0 dex) stars are identified in M 54. The evidence collected so far cannot be explained neither with a globular cluster-like scenario nor with a galactic chemical evolution. The chemical properties of M 54 can be explained within a scenario where this system formed through the merging of two globular clusters, the metal-poor one with standard characteristics and the more metal-rich one with more pronounced chemical anomalies, a possibly younger than the first one. M 54 is confirmed as a key stellar system for explaining the chemical evolution of a nuclear star cluster.

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arXiv2025

The Hubble Missing Globular Cluster Survey. II. Survey membership tools and kinematic analysis of NGC 6749

The Hubble Missing Globular Cluster Survey has secured high quality astro photometric data in two bands for 34 clusters never observed with HST. When combined with Gaia positional measurements, this data set enables the investigation of the bulk motion and the internal kinematics of these poorly studied clusters to an unprecedented level of detail. Focusing on the case of NGC 6749, we here showcase how the combined Gaia HST proper motions have a quality sufficient to accurately assess the cluster stellar membership, determine its absolute proper motion with a precision superior to Gaia, and to investigate its kinematic profile for the first time. Proper motions are determined using the public code GAIAHUB, which for NGC 6749 combines data sets separated in time by 8 years. The resulting measurements improve the precision of Gaia proper motions by a factor of 10 at the faint end, and enable recovering the proper motion for 662 stars for which Gaia could only measure the positions. These proper motions are efficient in decontaminating the colour magnitude diagram of NGC 6749, and make it possible to compare the efficacy of a method of statistical decontamination that relies only on the photometric information extracted from the HST parallel fields. Finally, using the sample of best measured proper motions we determine the velocity dispersion and anisotropy profiles of NGC 6749, that reveal an isotropic behaviour in the cluster inner regions and a slight radial anisotropy outside 1.5 half light radii. The proper motions and the code to statistically decontaminate the clusters color magnitude diagram are made available as public products of the survey.

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arXiv2025

KOALA, a new ATLAS9 database -- I. Model atmospheres, opacities, fluxes, bolometric corrections, magnitudes and colours

We present the KOALA database, a new set of LTE, line-blanketed model atmospheres calculated with the code ATLAS9, together with the corresponding Opacity Distribution Functions and emergent fluxes. The latter were used also to calculated G-band bolometric corrections and theoretical magnitudes and colours for several photometric systems, i.e. UBVRI, 2MASS, Hypparcos-Tycho, SDSS, Galex, Euclid and Gaia DR3. With respect to the previous grids of ATLAS9 model atmospheres, we adopted the solar mixture by Caffau/Lodders and we extend the sampling in metallicity (from -5.0 to -2.5 dex with step of 0.5 dex, and from -2.5 dex to +0.5 dex with step of 0.25 dex) and in [alfa/Fe] (from -0.4 to +0.4 dex with a step of 0.2 dex). Also, we provide a finer sampling in Teff for Teff lower than 7000 K. This finer grid allows for more accurate interpolation of colours and in many cases it makes not necessary to compute a new model atmosphere, since one of the grid can be used directly. A total of 51663 model atmospheres and emergent fluxes have been computed. Finally, we discuss the impact of [M/H] and [alfa/Fe] on the thermal and pressure structures of the model atmospheres and on theoretical colours.

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arXiv2025

A Walk on the Retrograde Side (WRS) project. II. Chemistry to disentangle in situ and accreted components in Thamnos

We present the results of the first systematic and dedicated high-resolution chemical analysis of the Thamnos substructure, a candidate relic of the process of hierarchical merger of the Milky Way. The analysis was perfomed in comparison with the Gaia-Sausage-Enceladus (GSE) remnant, within the fully self-consistent and homogeneous framework established by the 'A Walk on the Retrograde Side' (WRS) project. We analysed high-resolution and high signal-to-noise ratio spectra obtained with UVES at VLT for 212 red giant branch stars classified as candidate members of Thamnos and GSE, based on selections in the space of the integrals of motion. We derived precise abundances for 16 atomic species. Compared to GSE, stars attributed to the Thamnos substructure are, on average, more metal-poor, yet most of them show higher [X/Fe] abundance ratios in several elements, such as Na, Mg, Al, Ca, Cu, Zn, as well as lower [Eu/Fe]. The majority of candidate Thamnos stars show chemical signatures more consistent with the in situ Milky Way halo rather than a typical low-mass accreted dwarf galaxy. Our findings are further supported by comparisons with tailored galactic chemical evolution models, which fall short in reproducing the observed enhancement in the $\alpha$-elements, but are able to fit the more metal-poor component present in the Thamnos substructure. These results confirm a high level of contamination in the Thamnos substructure from the in situ population and to a lesser degree from GSE, while still leaving room for a genuine accreted population from a small disrupted dwarf galaxy.

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arXiv2025

Cluster Ages to Reconstruct the Milky Way Assembly (CARMA) IV. Chrono-dynamics of seven old star clusters in the Large Magellanic Cloud and the peculiar origin of NGC 1841

In this study, we report conclusive evidence for an ancient star cluster that has been accreted by the Large Magellanic Cloud (LMC). By leveraging observations from the Hubble Space Telescope (HST), we investigate the chrono-dynamical structure of a sample of seven old star clusters within the LMC in a self-consistent way. The multi-epoch nature of the dataset allowed the determination of high-precision proper motions for the clusters. Employing an isochrone-fitting methodology, we additionally infer from the deep high-resolution HST data homogeneous and robust estimates for their distances, ages and metallicities. Supplementing these data with literature line-of-sight velocities, we investigate the full 3-dimensional dynamics of the clusters within the frame of the LMC. With respect to the other clusters in our sample, NGC 1841 depicts a peculiar case. Its position in the age-metallicity plane, that makes it about 1 Gyr younger than the other metal-poor LMC clusters, but also its dynamical properties with a radial orbit almost perpendicular to the LMC disc plane, clearly advocates for a different origin. We thus conclude that NGC 1841 has likely been accreted by the LMC from a smaller galaxy. The other clusters in our sample show disc-like kinematics, with the case of NGC 2210 being peculiar, based on its inclined orbit. Their coherent age-metallicity relation closely resembles that of Gaia-Sausage-Enceladus globular clusters, thus suggesting a similar early evolution for the two dwarf galaxies. We do not find clear-cut chrono-kinematic evidence that NGC 2005 has been accreted by the LMC as suggested by a previous study based on its chemical abundance pattern. Regardless of its nature, its very old age illustrates that peculiar chemical evolutions already emerge at very early times.

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arXiv2025

Lithium evolution in the Galactic thin disc from Main-Sequence and early Red-Giant-Branch stars

The role of novae as producers of galactic lithium has been suggested since the 1970s, and it has been reconsidered recently with the detection of $^7$Be in their outbursts. At the same time, stellar models are moving forward to comprehend the discrepancy between the primordial lithium abundance predicted by the standard Big Bang Nucleosynthesis theory and the measured value of old dwarf stars. In this work, we follow the evolution of $^7$Li in the galactic thin disc starting from a primordial value of A(Li)=2.69 dex and applying $^7$Li depletion corrections of the stellar model with overshooting to our chemical evolution models. We use the upper envelope of the observational data to constrain the models. In addition to the dwarf main sequence (MS) stars, our analysis includes, for the first time, the early red-giant-branch (RGB) stars. Besides the renowned Spite plateau of the MS stars at low metallicities, we also confirm the existence of a second A(Li) plateau of the early RGB stars, which can be explained by our model with the corrections from stellar models. Our best-fit model is obtained with an effective averaged $^7$Li yield $^{Li}Y_\mathrm{Nova}=2.34\times 10^{-5} M_\odot$ during the whole lifetime of a nova. This reinforces the possibility that novae are the main galactic $^7$Li source, together with the stellar models' ability to comprehend the "cosmological lithium problem" in this context.

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arXiv2025

The Bulge Cluster Origin (BulCO) survey at the ESO-VLT: probing the early history of the Milky Way assembling. Design and first results in Liller1

We present the scientific goals and the very first results of the Bulge Cluster Origin (BulCO) survey. This survey has been specifically designed to perform an unprecedented chemical screening of stellar systems orbiting the Milky Way bulge, with the aim to unveil their true origin. It takes advantage of the improved performances of the spectrograph CRIRES+ operating at the ESO Very Large telescope, in the near-infrared domain. Due to the complex evolutionary history of the Milky Way, a variety of relics tracing different phenomena is expected to populate the Bulge: globular clusters formed in-situ or accreted from outside the Galaxy, nuclear star clusters of cannibalized structures, and possibly a few remnants of the proto-bulge formation process (the so-called ``bulge fossil fragments"). The signatures of the different origins are imprinted in the chemical properties of these stellar systems because specific abundance patterns provide authentic "chemical DNA" tests univocally tracing the enrichment process and, therefore, the environment where the stellar population formed. Thus, each system can provide a new piece of information on the bulge formation and evolutionary history. As first results of the survey, here we discuss the alpha-element and iron abundances of a sample of stars observed in the stellar system Liller 1, which is proposed to be a bulge fossil fragment. By combining this dataset with a recently published sample of high/mid-resolution spectra, we discuss the overall chemical properties of the stellar populations in Liller1, proving its link with the Galactic bulge and providing new constraints on its star formation history.

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arXiv2025

Cluster Ages to Reconstruct the Milky Way Assembly (CARMA). III. NGC 288 as the first Splashed globular cluster

The system of globular clusters (GCs) in the Milky Way (MW) comprises a mixture of both in situ and accreted clusters. Tracing the origin of GCs provides invaluable insights into the formation history of the MW. However, reconciling diverse strands of evidence is often challenging. A notable example is NGC 288, where despite significant efforts in the literature, the available chrono-chemodynamical data have yet to provide a definitive conclusion regarding its origin. On the one hand, all post-Gaia dynamical studies indicate an accreted origin for NGC 288 from the Gaia-Sausage-Enceladus (GSE) dwarf galaxy. On the other hand, NGC 288 has been found to be 2.5 Gyr older than other GSE GCs at the same metallicity, this suggesting a different (and possibly in situ) origin. In this work, we address the unresolved question on the origin of NGC 288 by analyzing its chrono-chemical properties in an unprecedentedly homogeneous framework. First, we compare the location of NGC 288 in the age-metallicity plane with that of other two in situ GCs at similar metallicity, namely NGC 6218 and NGC 6362. The age estimates obtained within the homogeneous framework of the CARMA collaboration show that the three clusters are coeval, reinforcing the contrast with the dynamical interpretation. Then, we compare the abundances with a sample of in situ and accreted clusters at similar metallicity, finding again consistency with the chemistry of in situ systems. To reconcile these results with its orbital properties, we propose a scenario where NGC 288 formed in the proto-disc of the MW, and then was dynamically heated by the interaction with the GSE merger. This is a fate that resembles that of proto-disc stars undergoing the so-called Splash event. Therefore, NGC 288 demonstrates the importance of a homogeneous chrono-chemodynamical information in the interpretation of the origin of MW GCs.

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arXiv2025

The $Hubble$ Missing Globular Cluster Survey. I. Survey overview and the first precise age estimate for ESO452-11 and 2MASS-GC01

We present the $Hubble$ Missing Globular Cluster Survey (MGCS), a $Hubble$ $Space$ $Telescope$ Treasury Program dedicated to the observation of all kinematically confirmed Milky Way globular clusters that missed previous $Hubble$ imaging. After introducing the aims of the programme and describing its target clusters, we showcase the first results of the survey. These are related to two clusters, one located at the edge of the Milky Way bulge and observed in optical bands, namely ESO452-11, and one located in the Galactic disc observed in the near-IR, namely 2MASS-GC01. For both clusters, the deep colour-magnitude diagrams obtained from the MGCS observations reach several magnitudes below their main-sequence turn-off and thus enable the first precise estimate of their age. By using the methods developed in the Cluster Ages to Reconstruct the Milky Way Assembly (CARMA) project, we find ESO452-11 to be an old metal-intermediate globular cluster, with ${\rm [M/H]}\simeq-0.80^{+0.08}_{-0.11}$ and an age of ${\rm t}=13.59^{+0.48}_{-0.69}$ Gyr. Its location on the age-metallicity relation makes it consistent with an in situ origin, in agreement with its dynamical properties. On the other hand, the results for 2MASS-GC01 highlight it as a young metal-intermediate cluster, with an age of ${\rm t}=7.22^{+0.93}_{-1.11}$ Gyr at ${\rm [M/H]}=-0.73^{+0.06}_{-0.06}$. Despite the large associated uncertainty, our age estimate for this extremely extincted cluster indicates it to be either the youngest globular cluster known to date or a massive and compact open cluster, which is consistent with its almost circular, disc-like orbit

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arXiv2025

MINCE III. Detailed chemical analysis of the UVES sample

Context. The MINCE (Measuring at Intermediate Metallicity Neutron-Capture Elements) project aims to provide high quality neutron-capture abundances measurements in several hundred stars at intermediate metallicity,-2.5 < [Fe/H] < -1.5. This project will shed light on the origin of the neutron-capture elements and the chemical enrichment of the Milky Way. Aims. The goal of this work is to chemically characterize the second sample of the MINCE project and compare the abundances with the galactic chemical evolution model at our disposal. Methods. We performed a standard abundance analysis based on 1D LTE model atmospheres on high-resolution and high-signal-to-noise-ratio UVES spectra. Results. We provide the kinematic classification (i.e., thin disk, thick disk, thin-to-thick disk, halo, Gaia Sausage Enceladus, Sequoia) of 99 stars and the atmospheric parameters for almost all stars. We derive the abundances for light elements (from Na to Zn) and neutron-capture elements (Rb, Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu) in a subsample of 32 stars in the metallicity range -2.5 < Fe/H] < -1.00. In the subsample of 32 stars, we identify 8 active stars exhibiting (inverse) P-Cygni profile and one Li-rich star, CD 28-11039. We find a general agreement between the chemical abundances and the stochastic model computed for the chemical evolution of the Milky Way halo for the elements Mg, Ca, Si, Ti, Sc, Mn, Co, Ni, Zn, Rb, Sr, Y, Zr, Ba, La, and Eu . Conclusions. The MINCE project has already significantly increased the number of neutron-capture elements measurements in the intermediate metallicity range. The results from this sample are in perfect agreement with the previous MINCE sample. The good agreement between the chemical abundances and the chemical evolution model of the Galaxy supports the nucleosynthetic processes adopted to describe the origin of the n-capture elements.

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arXiv2024

A comparative high-resolution spectroscopic analysis of in situ and accreted globular clusters

Globular clusters (GCs) are extremely intriguing systems that help in reconstructing the assembly of the Milky Way via the characterisation of their chemo-chrono-dynamical properties. In this study, we use high-resolution spectroscopic archival data from UVES and UVES-FLAMES at VLT to compare the chemistry of GCs dynamically tagged as either Galactic (NGC 6218, NGC 6522 and NGC 6626) or accreted from distinct merger events (NGC 362 and NGC 1261 from Gaia-Sausage-Enceladus, and Ruprecht 106 from the Helmi Streams) in the metallicity regime where abundance patterns of field stars with different origin effectively separate ($-1.3 \le$ [Fe/H] $\le -1.0$ dex). We find remarkable similarities in the abundances of the two Gaia-Sausage-Enceladus GCs across all chemical elements. They both display depletion in the $\alpha$-elements (Mg, Si and Ca) and statistically significant differences in Zn and Eu compared to in situ GCs. Additionally, we confirm that Ruprecht 106 exhibits a completely different chemical makeup from the other target clusters, being underabundant in all chemical elements. This demonstrates that when high precision is achieved, the abundances of certain chemical elements can not only efficiently separate in situ from accreted GCs, but can also distinguish among GCs born in different progenitor galaxies. In the end, we investigate the possible origin of the chemical peculiarity of Ruprecht 106. Given that its abundances do not match the chemical patterns of field stars associated to its most likely parent galaxy (i.e. the Helmi Streams), being depleted in the abundances of $\alpha$-elements in particular, we believe Ruprecht 106 to originate from a less massive galaxy compared to the progenitor of the Helmi Streams.

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arXiv2024

The true nature of HE0057-5959, the most metal-poor Li-rich star

The Li-rich stars are a class of rare objects with A(Li) higher than that of other stars in the same evolutionary stage. Their origin is still debated and valuable routes are the Cameron-Fowler mechanism, mass transfer process in a binary system or engulfment of small bodies. Metal-poor ([Fe/H]<-1 dex) stars are only a small fraction of the entire population of Li-rich stars. We observed with MIKE at the Magellan Telescope the metal-poor ([Fe/H]=-3.95+-0.11 dex) giant star HE0057-5959, deriving A(Li)=+2.09+-0.07 dex. Such A(Li) is higher by about 1 dex than that of other stars in the same evolutionary stage. A previous analysis of the same target suggested that its high A(Li) reflects a still ongoing First Dredge-Up process. We revise the nature of HE0057-5959 by comparing its stellar parameters and A(Li) with appropriate stellar evolution models. This comparison rules out that HE0057-5959 is caught during its First Dredge-Up, being this latter already ended according to the parameters of this star. Its A(Li), remarkably higher than the typical lithium plateau drawn by similar giant stars, demonstrates that HE0057-5959 joins the class of the rare metal-poor Li-rich stars. HE0057-5959 is the most metal-poor Li-rich star discovered so far. We consider different scenarios to explain this star. No internal mixing able to activate the Cameron-Fowler mechanism is known for metal-poor stars at this evolutionary stage. Also the engulfment of planets is disfavored because such metal-poor stars should not host planets. Finally, HE0057-5959 is one of the most Na-rich among the Li-rich stars and we found that a strong excess of Na is common to the three Li-rich stars with [Fe/H]<-3 dex. This finding could support the scenario of mass transfer from a massive companion star in a binary system, even if we found no evidence of radial velocity variations.

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arXiv2024

Detailed chemical abundances of the globular cluster Terzan 6 in the inner bulge

We used near-infrared spectroscopy at medium-high resolution (R=8,000$-$25,000) to perform the first comprehensive chemical study of the intermediate luminosity bulge globular cluster Terzan~6. We derived detailed abundances and abundance patterns of 27 giant stars, likely members of Terzan~6, based on their accurate Hubble Space Telescope proper motions and line-of-sight radial velocities. From the spectral analysis of these stars, we determined an average heliocentric radial velocity of 143.3$\pm$1.0 km s$^{-1}$ with a velocity dispersion of 5.1$\pm$0.7 km s$^{-1}$ and an average [Fe/H]=$-0.65\pm0.01$ and a low 1$σ$ dispersion of 0.03 dex. We also measured some depletion of [Mn/Fe] with respect to the solar-scaled values and enhancement of for [Ca/Fe], [Si/Fe], [Mg/Fe], [Ti/Fe], [O/Fe], [Al/Fe], [Na/Fe], and, to a lower extent, for [K/Fe], consistent with previous measurements of other bulge globular clusters and favoring the scenario of a rapid bulge formation and chemical enrichment. Some spread in the light element abundances suggest the presence of first- and second-generation stars, typical of genuine globulars. Finally, we measured some depletion of carbon and low $\rm ^{12}C/^{13}C$ isotopic ratios, as in previous studies of field and cluster bulge giants, indicating that extra-mixing mechanisms should be at work during the post main sequence evolution in the high metallicity regime as well.

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