Lithium abundance of post-T Tauri stars in Yssa and Gaya associations

Details Lithium abundance of post-T Tauri stars in Yssa and Gaya associations Lithium abundance of post-T Tauri stars in Yssa and Gaya associations

Aug 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003basbr..23..107d&link_type=abstract

Boletim da Sociedade Astronômica Brasileira (ISSN 0101-3440), vol.23, no.1, p.107-108

Astronomy and Astrophysics

Astronomy

3

Scientific paper

We present the results of the Li abundance determination for Post-T Tauri stars belonging to Young Scorpius Sagitarius Association (YSSA), t £ 10 Myr, and Great Austral Young Association (GAYA), t~30 Myr, based on high-resolution spectra obtained at 1.52 m telescope with FEROS at ESO. We derived Li abundances by means of synthetic-spectrum calculations using two Li i lines: the resonance one at 6708 Å and the secondary line at 6104 Å. It is well known that the presence of strong Li lines in T Tauri and Post-T Tauri stars is an indication of their youth. As evolution proceeds, Li abundance decreases by depletion. Thus, Li could serve as a "clock" of stellar evolution in the pre-main-sequence (PMS) phase. This is why a precise determination of the Li abundance is very important for a reliable estimation of the PMS star's age. However, measurement of Li abundance for these very active young stars is a difficult task. The commonly used resonance Li i line is formed in high photospheric and even low chromospheric layers, perturbed by the stellar activity, which, in turn, results in too high values of Li abundances derived from this line. The largest difference in the Li abundances obtained using two Li i lines appears in the case of the younger association - YSSA. Almost all members of this association show LTE Li abundances derived from the resonance line at 6708 Å larger than that of the interstellar medium (ISM), whereas Li abundances determined using the secondary line have near ISM values. In the case of GAYA this difference is not so pronounced. This effect can be explained by the fact that the stars of the very young YSSA association have more active outer atmospheres. We compared derived Li abundances with predictions from evolutionary models. Analysis of Li abundance of the low-mass (~0.7-0.8M¤) members of GAYA shows that these stars have already significantly depleted their initial lithium. This confirms thereby that contemporary theoretical evolutionary models predict a too slow Li depletion.

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