Proceedings of the conference "Lithium in the Universe: To Be or not to Be?", held at Rome Observatory, 18-22 November , 2019; in press for the Mem. Società Astronomica Italiana (4 pages and 3 figure)
Recently, we studied the chemical evolution of lithium in the thin disc of the Milky Way. We found that the best agreement with the observed Li abundances in the thin disc is obtained considering novae as the main source of lithium. We assumed a delay time of ~1 Gyr for nova production and an effective 7Li yield of 1.8($\pm$0.6)x10$^{-5}$ Msun over the whole nova lifetime. The possibility to check our detailed assumptions on lithium production on other stellar systems, such as the satellites of our Milky Way, is seriously hampered by their distance from us. In these systems dwarf stars (where the original lithium can be measured) are too faint to detect lithium lines. However, thanks to the Gaia mission, it was recently possible to disentangle the stars of a disrupted dwarf galaxy in the Galactic halo (called Enceladus or Galactic sausage). Adopting a chemical evolution model tuned to match the metallicity distribution function of Enceladus stars, we present our predictions for the lithium abundance of the stars of this disrupted galaxy.
This contribution presents an overview of the evolution of Li abundances in stars of the Galactic thin and thick discs, from the observational point of view. The focus is on Li abundances obtained by recent projects and surveys. To separate thin and thick disc stars, both chemical abundances, kinematics, and ages can be used. For thick disc stars, the Li evolution is uncertain, as differences appear depending on how the stars were separated. Nevertheless, it seems clear that most of the Galactic enrichment in Li takes place in the thin disc. Literature consensus also seems to exist regarding t…
We revisit large spectroscopic data sets for field stars from the literature to derive the upper Li envelope in the high metallicity regime in our Galaxy. We take advantage of Gaia EDR3 data and state-of-the-art stellar models to precisely determine the position of the sample dwarf stars in the Hertzsprung-Russell diagram. The highest Li abundances are found in field metal-rich warm dwarfs from the GALAH survey, located on the hot side of the Li-dip. Their mean Li value agrees with what was recently derived for warm dwarfs in metal-rich clusters, pointing towards a continuous increase of Li up…
Data from Gaia DR2 and APOGEE surveys revealed a relatively new component in the inner Galactic halo, which is likely the dynamical remnant of a disrupted dwarf galaxy named Gaia-Enceladus that collided with the Milky Way about 10 Gyrs ago. This merging event offers an extraordinary opportunity to study chemical abundances of elements in a dwarf galaxy, since they are generally hampered in external galaxies. Here, we focus on Li and Be in dwarf stars which are out of reach even in Local Group galaxies.Searching in GALAH, Gaia-ESO survey and in literature, we found several existing 7Li abundanc…
The cosmological {7Li problem consists in explaining why the primordial Li abundance, as predicted by the standard Big Bang nucleosynthesis theory with constraints from WMAP and Planck, is a factor of 3 larger than the Li abundance measured in the stars of the Spite plateau defined by old, warm dwarf stars of the Milky Way halo. Several explanations have been proposed to explain this difference, including various Li depletion processes as well as non standard Big Bang nucleosynthesis, but the main question remains unanswered. In this paper, we present detailed chemical evolution models for dwa…
The Gaia-ESO Survey (GES) is a large public spectroscopic survey that was carried out using the multi-object FLAMES spectrograph at the Very Large Telescope. The survey provides accurate radial velocities, stellar parameters, and elemental abundances for ~115,000 stars in all Milky Way components. In this paper we describe the method adopted in the final data release to derive lithium equivalent widths (EWs) and abundances. Lithium EWs were measured using two different approaches for FGK and M-type stars, to account for the intrinsic differences in the spectra. For FGK stars, we fitted the lit…
Recent detection of the isotope $^7$Be (that decays into $^7$Li) in the outburst of classical novae confirms the suggestion made in the 70s that novae could make $^7$Li. We reconsidered the role of novae as producers of Li by means of a detailed model of the chemical evolution of the Milky Way. We showed that novae could be the Galactic lithium source accounting for the observed increase of Li abundances in the thin disk with stellar metallicity. The best agreement with the upper envelope of the observed Li abundances is obtained for a delay time of ~ 1 Gyr for the nova production and for an e…
Of all the light elements, the evolution of lithium (Li) in the Milky Way is perhaps the most difficult to explain. Li is difficult to synthesize and is easily destroyed, making most stellar sites unsuitable for producing Li in sufficient quantities to account for the proto-solar abundance. For decades, novae have been proposed as a potential explanation to this 'Galactic Li problem', and the recent detection of 7Be in the ejecta of multiple nova eruptions has breathed new life into this theory. In this work, we assess the viability of novae as dominant producers of Li in the Milky Way. We pre…
We present the results of a multi-technique investigation of the M4.5Ve flare star AP Col, which we discover to be the nearest pre-main-sequence star. These include astrometric data from the CTIO 0.9m, from which we derive a proper motion of 342.0+/-0.5 mas yr^-1, a trigonometric parallax of 119.21+/-0.98 mas (8.39+/-0.07 pc), and photometry and photometric variability at optical wavelengths. We also provide spectroscopic data, including radial velocity (22.4+/-0.3 km s^-1), lithium Equivalent Width (EW) (0.28+/-0.02 A), H-alpha EW (-6.0 to -35 A), {\it vsini} (11+/-1 km s^-1), and gravity ind…
The observed amount of lithium for low metallicity population II stars (known as the Spite plateau) is a factor of $\sim 3-5$ lower than the predictions of the standard cosmology. Since the observations are limited to the local Universe (halo stars, globular clusters and satellites of the Milky Way) it is possible that certain physical processes may have led to the spatial separation of lithium and local reduction of [Li/H]. We study the question of lithium diffusion after the cosmological recombination in sub-Jeans dark matter haloes, taking into account that more than 95% of lithium remains …
The lithium abundance, A(Li), in stellar atmospheres suffers from various enhancement and depletion processes during the star's lifetime. While several studies have demonstrated that these processes are linked to the physics of stellar formation and evolution, the role that Galactic-scale events play in the galactic A(Li) evolution is not yet well understood. We aim to demonstrate that the observed A(Li) bi-modal distribution, in particular in the FGK-dwarf population, is not a statistical artefact and that the two populations connect through a region with a low number of stars. We also want t…
We report the results of an unsupervised decomposition of the local stellar halo in the chemo-dynamical space spanned by the abundance measurements from APOGEE DR17 and GALAH DR3. In our Gaussian Mixture Model, only four independent components dominate the halo in the Solar neighborhood, three previously known $Aurora$, $Splash$ and Gaia-Sausage/Enceladus (GS/E) and one new, $Eos$. Only one of these four is of accreted origin, namely the GS/E, thus supporting the earlier claims that the GS/E is the main progenitor of the Galactic stellar halo. We show that $Aurora$ is entirely consistent with …
The surface content of lithium (Li) and beryllium (Be) in stars can reveal important information about the temperature structure and physical processes in their interior regions. This study focuses on solar-type stars with a sample that is more precisely defined than done previously. Our selection of stars studied for Be is constrained by five parameters: mass, temperature, surface gravity, metallicity, and age to be similar to the Sun and is focussed on stars within +-0.02 of 1 M_sun. We have used the Keck I telescope with HIRES to obtain spectra of the Be II spectral region of 52 such stars …
In order to characterize 22 new globular cluster (GC) candidates in the Galactic bulge, we present their colour-magnitude diagrams (CMDs) and Ks-band luminosity functions (LFs) using the near-infrared VVV database as well as Gaia-DR2 proper motion dataset. CMDs were obtained, on one hand, after properly decontaminating the observed diagrams from background/foreground disc stars and other sources. On the other hand, CMDs were also obtained based upon star selection in proper motion diagrams. Taking into account our deep CMDs and LFs analyses, we find that 17 out of 22 new GC candidates may be r…
Exploring the Galactic chemical evolution and enrichment scenarios with open clusters allows us to understand the history of the Milky Way disk. High-resolution spectra of OCs are a crucial tool, as they provide precise chemical information, to combine with precise distances and ages. The aim of the Stellar Population Astrophysics project is to derive homogeneous and accurate comprehensive chemical characterization of a number of poorly studied OCs.Using the HARPS-N echelle spectrograph at the Telescopio Nazionale Galileo, we obtained high-resolution spectra of giant stars in 18 OCs, 16 of whi…
A discrepancy has emerged between the cosmic lithium abundance inferred by the WMAP satellite measurement coupled with the prediction of the standard big-bang nucleosynthesis theory, and the constant Li abundance measured in metal-poor halo dwarf stars (the so-called Spite plateau). Several models are being proposed to explain this discrepancy, involving either new physics, in situ depletion, or the efficient depletion of Li in the pristine Galaxy by a generation of massive first stars. The realm of possibilities may be narrowed considerably by observing stellar populations in different galaxi…
We aim to constrain the mixing processes in low-mass stars by investigating the behaviour of the Li surface abundance after the main sequence. We take advantage of the data from the sixth internal data release of Gaia-ESO, idr6, and from the Gaia Early Data Release 3, edr3. We select a sample of main sequence, sub-giant, and giant stars in which Li abundance is measured by the Gaia-ESO survey, belonging to 57 open clusters with ages from 120~Myr to about 7 Gyr and to Milky Way fields, covering a range in [Fe/H] between -1.0 and +0.5dex. We study the behaviour of the Li abundances as a function…
Similarities in the chemical composition of two of the closest Milky Way satellites, namely the Large Magellanic Cloud (LMC) and the Sagittarius (Sgr) dwarf galaxy, have been proposed in the literature, suggesting similar chemical enrichment histories between the two galaxies. This proposition, however, rests on different abundance analyses, which likely introduce various systematics that hamper a fair comparison among the different data sets. In order to bypass this issue (and highlight real similarities and differences between their abundance patterns), we present a homogeneous chemical anal…
Metal-poor stars in the Milky Way are local relics of the epoch of the first stars and the first galaxies. However, a low metallicity does not prove that a star formed in this ancient era, as metal-poor stars form over a range of redshift in different environments. Theoretical models of Milky Way formation have shown that at constant metallicity, the oldest stars are those closest to the center of the Galaxy on the most tightly-bound orbits. For that reason, the most metal-poor stars in the bulge of the Milky Way provide excellent tracers of the chemistry of the high-redshift universe. We repo…
The idea behind FIRST (Fibered Imager foR a Single Telescope) is to use single-mode fibers to combine multiple apertures in a pupil plane as such as to synthesize a bigger aperture. The advantages with respect to a pure imager are i) relaxed tolerance on the pointing and cophasing, ii) higher accuracy in phase measurement, and iii) availability of compact, precise, and active single-mode optics like Lithium Niobate. The latter point being a huge asset in the context of a space mission. One of the problems of DARWIN or SIM-like projects was the difficulty to find low cost pathfinders missions. …
The cosmological Li problem is the observed discrepancy between Li abundance, A(Li), measured in Galactic dwarf, old and metal-poor stars (traditionally assumed to be equal to the initial value A(Li)_0), and that predicted by standard Big Bang Nucleosynthesis calculations (A(Li)_{BBN}). Here we attack the Li problem by considering an alternative diagnostic, namely the surface Li abundance of red giant branch stars that in a colour magnitude diagram populate the region between the completion of the first dredge-up and the red giant branch bump. We obtained high-resolution spectra with the FLAME…
Metal-poor stars hold the key to our understanding of the origin of the elements and the chemical evolution of the Universe. This chapter describes the process of discovery of these rare stars, the manner in which their surface abundances (produced in supernovae and other evolved stars) are determined from the analysis of their spectra, and the interpretation of their abundance patterns to elucidate questions of origin and evolution. More generally, studies of these stars contribute to other fundamental areas that include nuclear astrophysics, conditions at the earliest times, the nature of th…
Globular clusters are large and dense agglomerate of stars. At variance with smaller clusters of stars, they exhibit signs of some chemical evolution. At least for this reason, they are intermediate between open clusters and massive objects such as nuclear clusters or compact galaxies. While some facts are well established, the increasing amount of observational data are revealing a complexity that has so far defied the attempts to interpret the whole data set in a simple scenario. We review this topic focusing on the main observational features of clusters in the Milky Way and its satellites.…
Stars destroy lithium (Li) in their normal evolution. The convective envelopes of evolved red giants reach temperatures of millions of K, hot enough for the 7Li(p,alpha)4He reaction to burn Li efficiently. Only about 1% of first-ascent red giants more luminous than the luminosity function bump in the red giant branch exhibit A(Li) > 1.5. Nonetheless, Li-rich red giants do exist. We present 15 Li-rich red giants--14 of which are new discoveries--among a sample of 2054 red giants in Milky Way dwarf satellite galaxies. Our sample more than doubles the number of low-mass, metal-poor ([Fe/H] <~ -0.…
