Lithium and Beryllium in One-solar-mass Stars

Abstract

Abstract The surface content of lithium (Li) and beryllium (Be) in stars can reveal important information about the temperature structure and physical processes in their interior regions. This study focuses on solar-type stars with a sample that is more precisely defined than done previously. Our selection of stars studied for Be is constrained by five parameters: mass, temperature, surface gravity, metallicity, and age to be similar to the Sun and is focused on stars within ±0.02 of 1 M ⊙. We have used the Keck I telescope with HIRES to obtain spectra of the Be ii spectral region of 52 such stars at a high spectral resolution (∼45,000) and high signal-to-noise ratios. While the spread in Li in these stars is greater than a factor of 400, the spread in Be is only 2.7 times. Two stars were without any Be, perhaps due to a merger or a mass transfer with a companion. We find a steep trend of Li with temperature but little for Be. While there is a downward trend in Li with [Fe/H] from −0.4 to +0.4 due to stellar depletion, there is a small increase in Be with Fe from Galactic Be enrichment. While there is a broad decline in Li with age, there may be a small increase in Be with age, though age is less well determined. In the subset of stars closest to the Sun in temperature and other parameters, we find that the ratio of the abundances of Be to Li is much lower than predicted by models; there may be other mixing mechanisms causing additional Li depletion.