EDP Sciences
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Volume 412, Number 1, December II 2003
Page(s) 213 - 218
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20031410

A&A 412, 213-218 (2003)
DOI: 10.1051/0004-6361:20031410

Efficiency of convection and Pre-Main Sequence lithium depletion

F. D'Antona1 and J. Montalbán2

1  INAF, Osservatorio Astronomico di Roma, 00040 Monteporzio, Italy
2  Institut d'Astrophysique et de Géophysique, Université de Liège, 4000 Liège, Belgium

(Received 21 February 2003 / Accepted 5 August 2003 )

We show by detailed model computation how much the Pre-Main Sequence (PMS) lithium depletion depends on the treatment of over-adiabaticity, by taking advantage of the results of new models by Montalbán et al., which apply different treatments of convection to non-grey PMS models. In order to reproduce both the PMS lithium depletion (inferred from the lithium depletion patterns in young open clusters), and the location of PMS tracks in the HR diagram (inferred from the study of young PMS stars), convection both in the atmosphere and in a good fraction of the stellar envelope must be highly inefficient: e.g., in the Mixing Length Theory approximation, it must have a very low $\alpha=l/H_{\rm p}$. Unfortunately, the radii of these models are at variance with the solar radius, possibly indicating that there is some additional physical input, generally not taken into account in the stellar models, which affects the efficiency of convection in PMS stars, but probably not in the main sequence stars nor in evolved red giants. We stress the importance of determining precisely masses and lithium abundance in PMS binaries such as the important spectroscopic and eclipsing binary RXJ 0529.4+0041.

Key words: stars: evolution -- stars: atmospheres -- convection -- stars: pre main sequence

Offprint request: F. D'Antona, dantona@coma.mporzio.astro.it

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