Navegando por Autor "Richard, O."
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Artigo Lithium abundances and extra mixing processes in evolved stars of M 67(Astronomy & Astrophysics, 2011) Martins, B. L. Canto; Lèbre, A.; Palacios, A.; Laverny, P. de; Richard, O.; Melo, C. H. F.; Nascimento Jr, J. D. do; Medeiros, José Renan deAims. We present a spectroscopic analysis of a sample of evolved stars in M 67 (turn-off, subgiant and giant stars) in order to bring observational constraints to evolutionary models taking into account non-standard transport processes. Methods. We determined the stellar parameters (Teff, log g, [Fe/H]), microturbulent and rotational velocities and, lithium abundances (ALi) for 27 evolved stars of M 67 with the spectral synthesis method based on MARCS model atmospheres. We also computed non-standard stellar evolution models, taking into account atomic diffusion and rotation-induced transport of angular momentum and chemicals that were compared with this set of homogeneous data. Results. The lithium abundances that we derive for the 27 stars in our sample follow a clear evolutionary pattern ranging from the turn-off to the Red Giant Branch. Our abundance determination confirms the well known decrease of lithium content for evolved stars. For the first time, we provide a consistent interpretation of both the surface rotation velocity and of the lithium abundance patterns observed in an homogeneous sample of TO and evolved stars of M 67. We show that the lithium evolution is determined by the evolution of the angular momentum through rotation-induced mixing in low-mass stars, in particular for those with initial masses larger than 1.30 M when at solar metallicity.Artigo S1242: a lithium-rich subgiant star in the open cluster M 67(Astronomy & Astrophysics, 2006-05-04) Martins, B. L. Canto; Lèbre, A.; Laverny, P. de; Melo, C. H. F.; Nascimento Jr, J. D. do; Richard, O.; Medeiros, José Renan deAims. We report the serendipitous discovery of a lithium-rich subgiant star, S1242. This object is member of a large eccentricity spectroscopic binary system in the solar-age open cluster M 67. Methods. Using VLT/FLAMES-UVES observations and synthetic spectrum analysis, we derived for this star stellar parameters (temperature, gravity, metallicity and rotational velocity) and a surface Li abundance (ALi = 2.7) larger than the higher abundance of M 67 stars near the turn-off. Results. The high Li abundance we found in S1242 points to an excess of lithium at the subgiant stage. We discuss two possible explanations for this unusually high Li content in this binary system: a preservation of the Li at the turn-off stage due to tidal effects, or an efficient dredge-up of Li, hidden below the convective zone by atomic diffusion occuring in the post turn-off stage.