Navegando por Autor "Meléndez, J."
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Artigo Age and mass of solar twins constrained by lithium abundance(Astronomy & Astrophysics, 2009) Nascimento Jr, J. D. do; Castro, M.; Meléndez, J.; Bazot, M.; Théado, S.; Mello, G. F. Porto de; Medeiros, José Renan deAims. We analyze the non-standard mixing history of the solar twins HIP 55 459, HIP 79 672, HIP 56 948, HIP 73 815, and HIP 100 963, to determine as precisely as possible their mass and age. Methods. We computed a grid of evolutionary models with non-standard mixing at several metallicities with the Toulouse-Geneva code for a range of stellar masses assuming an error bar of ±50 K in Teff. We choose the evolutionary model that reproduces accurately the observed low lithium abundances observed in the solar twins. Results. Our best-fit model for each solar twin provides a mass and age solution constrained by their Li content and Teff determination. HIP 56 948 is the most likely solar-twin candidate at the present time and our analysis infers a mass of 0.994 ± 0.004 M and an age of 4.71 ± 1.39 Gyr. Conclusions. Non-standard mixing is required to explain the low Li abundances observed in solar twins. Li depletion due to additional mixing in solar twins is strongly mass dependent. An accurate lithium abundance measurement and non-standard models provide more precise information about the age and mass more robustly than determined by classical methods alone.Artigo Shallow extra mixing in solar twins inferred from Be abundances(EDP Sciences, 2015-03-10) Maia, M. Tucci; Meléndez, J.; Castro, M.; Asplund, M.; Ramírez, I.; Monroe, T. R.; Nascimento Júnior, José Dias do; Young, D.Context. Lithium and beryllium are destroyed at different temperatures in stellar interiors. As such, their relative abundances offer excellent probes of the nature and extent of mixing processes within and below the convection zone. Aims. We determine Be abundances for a sample of eight solar twins for which Li abundances have previously been determined. The analyzed solar twins span a very wide range of age, 0.5–8.2 Gyr, which enables us to study secular evolution of Li and Be depletion. Methods. We gathered high-quality UVES/VLT spectra and obtained Be abundances by spectral synthesis of the Be ii 313 nm doublet. Results. The derived beryllium abundances exhibit no significant variation with age. The more fragile Li, however, exhibits a monotonically decreasing abundance with increasing age. Therefore, relatively shallow extra mixing below the convection zone is necessary to simultaneously account for the observed Li and Be behavior in the Sun and solar twinsArtigo Solar twins in M 67: evolutionary status and lithium abundance(Astronomy & Astrophysics, 2011) Castro, M.; Nascimento Jr., J. D. do; Biazzo, K.; Meléndez, J.; Medeiros, José Renan deAims. We determine the age and mass of the three best solar twin candidates in open cluster M 67 through lithium evolutionary models. Methods. We computed a grid of evolutionary models with non-standard mixing at metallicity [Fe/H] = 0.01 with the ToulouseGeneva evolution code for a range of stellar masses. We estimated the mass and age of 10 solar analogs belonging to the open cluster M 67. We made a detailed study of the three solar twins of the sample, YPB637, YPB1194, and YPB1787. Results. We obtained a very accurate estimation of the mass of our solar analogs in M 67 by interpolating in the grid of evolutionary models. The three solar twins allowed us to estimate the age of the open cluster, which is 3.87+0.55 −0.66 Gyr, which is better constrained than former estimates. Conclusions. Our results show that the 3 solar twin candidates have one solar mass within the errors and that M 67 has a solar age within the errors, validating its use as a solar proxy. M 67 is an important cluster when searching for solar twins.