Lithium in the symbiotic Mira V407 Cyg

Astronomy & Astrophysics, 2012

Lithium abundances in open clusters are a very effective probe of mixing processes, and their study can help us to understand the large depletion of lithium that occurs in the Sun. Owing to its age and metallicity, the open cluster M67 is especially interesting on this respect. Many studies of lithium abundances in M67 have been performed, but a homogeneous global analysis of lithium in stars from subsolar masses and extending to the most massive members, has yet to be accomplished for a large sample based on high-quality spectra. Aims. We test our non-standard models, which were calibrated using the Sun with observational data. Methods. We collect literature data to analyze, for the first time in a homogeneous way, the non-local thermal equilibrium lithium abundances of all observed single stars in M67 more massive than ∼ 0.9 M ⊙ . Our grid of evolutionary models is computed assuming a non-standard mixing at metallicity [Fe/H] = 0.01, using the Toulouse-Geneva evolution code. Our analysis starts from the entrance in the zero-age main-sequence. Results. Lithium in M67 is a tight function of mass for stars more massive than the Sun, apart from a few outliers. A plateau in lithium abundances is observed for turn-off stars. Both less massive (M ≤ 1.10 M ⊙ ) and more massive (M ≥ 1.28 M ⊙ ) stars are more depleted than those in the plateau. There is a significant scatter in lithium abundances for any given mass M ≤ 1.1 M ⊙ . Conclusions. Our models qualitatively reproduce most of the features described above, although the predicted depletion of lithium is 0.45 dex smaller than observed for masses in the plateau region, i.e. between 1.1 and 1.28 solar masses. More work is clearly needed to accurately reproduce the observations. Despite hints that chromospheric activity and rotation play a role in lithium depletion, no firm conclusion can be drawn with the presently available data.

Astronomy & Astrophysics, 2011

Aims. In this letter we characterise IRAS 12556-7731 as the first lithium-rich M-type giant. Based on its late spectral type and high lithium content, and because of its proximity in angular distance to the Chamaeleon II star-forming region, the star was misclassified as a young low-mass star in a previous work. Methods. Based on HARPS data, synthetic spectral modelling, and proper motions, we derive the astrophysical parameters and kinematics of the star and discuss its evolutionary status.

Astronomy and Astrophysics, 2009

Context. Most globular clusters are believed to host a single stellar population. They can thus be considered a good place to study the Spite plateau and to search for possible evolutionary modifications of the Li content. Aims. We want to determine the Li content of subgiant (SG) and main sequence (MS) stars of the old, metal-poor globular cluster NGC 6397. This work was aimed not only at studying possible Li abundance variations but also to investigate the cosmological Li discrepancy.

Proceedings of the International Astronomical Union, 2004

An internacional project "Lithium in magnetic Ap stars" has been run since 1996 with the purpose of creating an observational database allowing systematic studies of the abnormal occurence of lithium on the surface of cool Ap stars. The 2.6 m telescope at the Crimean Astrophysical Observatory, the ESO CAT, ESO 1.52 m telescope with FEROS, the Nordic Optical Telescope, and the 74" telescope at Mount Stromlo were employed to collect observations at the regions of the lithium resonance lines λ 6103 and λ 6708Å.

Astronomy & Astrophysics, 2016

Context. The chemical evolution of lithium in the Milky Way represents a major problem in modern astrophysics. Indeed, lithium is, on the one hand, easily destroyed in stellar interiors, and, on the other hand, produced at some specific stellar evolutionary stages that are still not well constrained. Aims. The goal of this paper is to investigate the lithium stellar content of Milky Way stars in order to put constraints on the lithium chemical enrichment in our Galaxy, in particular in both the thin and thick discs. Methods. Thanks to high-resolution spectra from the ESO archive and high quality atmospheric parameters, we were able to build a massive and homogeneous catalogue of lithium abundances for 7300 stars derived with an automatic method coupling, a synthetic spectra grid, and a Gauss-Newton algorithm. We validated these lithium abundances with literature values, including those of the Gaia benchmark stars. Results. In terms of lithium galactic evolution, we show that the interstellar lithium abundance increases with metallicity by 1 dex from [M/H] = −1 dex to +0.0 dex. Moreover, we find that this lithium ISM abundance decreases by about 0.5 dex at super-solar metalllicity. Based on a chemical separation, we also observed that the stellar lithium content in the thick disc increases rather slightly with metallicity, while the thin disc shows a steeper increase. The lithium abundance distribution of α-rich, metal-rich stars has a peak at A Li ∼ 3 dex. Conclusions. We conclude that the thick disc stars suffered of a low lithium chemical enrichment, showing lithium abundances rather close to the Spite plateau while the thin disc stars clearly show an increasing lithium chemical enrichment with the metallicity, probably thanks to the contribution of low-mass stars.

We present high resolution observations (FWHM=15 km s −1 ) of the Li region in 5 stars belonging to the old (≈14 Gyrs), metal rich ([Fe/H]≈-0.7) globular cluster 47Tuc. At the ESO NTT telescope we obtained EMMI spectra for three V∼17.4 magnitude stars located at the turnoff with T ef f on the Spite plateau. In two of the turnoff stars the lithium line is clearly detected and the mean lithium content [Li] = 2.37± 0.08±0.07 is derived. This value is slightly higher than the Spite plateau at [Li]=2.19±0.016 for field halo stars obtained with the same T ef f scale by .

Chemical Physics Letters, 1982