Lithium Depletion in Fully Convective Pre-Main-Sequence Stars
Abstract
We present an analytic calculation of the thermonuclear depletion of lithium in contracting, fully convective, pre-main-sequence stars of mass M <~ 0.5 M⊙. Previous numerical work relies on still uncertain physics (atmospheric opacities and convection, in particular) to calculate the effective temperature as a unique function of stellar mass. We assume that the star's effective temperature, Teff, is fixed during Hayashi contraction and allow its actual value to be a free parameter constrained by observation. Using this approximation, we compute lithium burning analytically and explore the dependence of lithium depletion on Teff, M, and composition. Our calculations yield the radius, age, and luminosity of a pre-main-sequence star as a function of lithium depletion. This allows for more direct comparisons with observations of lithium-depleted stars. Our results agree with those numerical calculations that explicitly determine stellar structure during Hayashi contraction. In agreement with Basri, Marcy, & Graham, we show that the absence of lithium in the Pleiades star HHJ 3 implies that it is older than 100 Myr. We also suggest a generalized method for dating Galactic clusters younger than 100 Myr (i.e., those with contracting stars of M >~ 0.08 M⊙) and for constraining the masses of lithium-depleted stars.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- June 1997
- DOI:
- arXiv:
- arXiv:astro-ph/9612155
- Bibcode:
- 1997ApJ...482..442B
- Keywords:
-
- Nuclear Reactions;
- Nucleosynthesis;
- Abundances;
- Stars: Evolution;
- Stars: Interiors;
- Stars: Pre-Main-Sequence;
- Astrophysics
- E-Print:
- 13 pages, LaTex with 2 postscript figures, uses aaspp4.sty and epsfig.sty, to appear in the Astrophysical Journal
