Beryllium anomalies in solar-type field stars^*

¹ Centro de Astronomia e Astrofísica da Universidade de Lisboa, Observatório Astronómico de Lisboa, Tapada da Ajuda, 1349-018 Lisboa, Portugal e-mail: nuno.santos@oal.ul.pt
² Observatoire de Genève, 51 Ch. des Maillettes, 1290 Sauverny, Switzerland
³ Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain
⁴ INAF/Osservatorio Astrofisico di Arcetri, Largo Fermi 5, 50125 Firenze, Italy
⁵ Departamento de Astrofísica, Universidad de La Laguna, Av. Astrofísico Francisco Sánchez s/n, 38206, La Laguna, Tenerife, Spain
⁶ Consejo Superior de Investigaciones Científicas, Spain

Received: 24 March 2004
Accepted: 11 June 2004

Abstract

We present a study of beryllium (Be) abundances in a large sample of field solar-type dwarfs and sub-giants spanning a large range of effective temperatures. The Be abundances, computed using a very uniform set of stellar parameters and near-UV spectra obtained with 3 different instruments, are used to study the depletion of this light element. The analysis shows that Be is severely depleted for F stars, as expected by the light-element depletion models. However, we also show that beryllium abundances decrease with decreasing temperature for stars cooler than ~6000 K, a result that cannot be explained by current theoretical models including rotational mixing, but that is, at least in part, expected from the models that take into account internal wave physics. In particular, the light element abundances of the coolest and youngest stars in our sample suggest that Be, as well as lithium (Li), has already been burned early during their evolution. Furthermore, we find strong evidence for the existence of a Be-gap for solar-temperature stars. The analysis of Li and Be abundances in the sub-giants of our sample also shows the presence of one case that has still detectable amounts of Li, while Be is severely depleted. Finally, we compare the derived Be abundances with Li abundances derived using the same set of stellar parameters. This gives us the possibility to explore the temperatures for which the onset of Li and Be depletion occurs.