Scenarios to explain extreme Be depletion in solar-like stars: accretion or rotation effects?

Physics and Astronomy, University of Exeter, Stocker Road, EX4 4, QL Exeter, UK
e-mail: mviallet@astro.ex.ac.uk; i.baraffe@exeter.ac.uk

Received: 19 April 2012
Accepted: 14 August 2012

Abstract

Studies of beryllium abundance in large samples of solar-type stars show a small fraction of extremely beryllium-deficient stars, which challenges our current understanding of light element depletion in these stars. We suggest two possible scenarios that may explain this high level of Be depletion: early accretion and rotational mixing. We show that in both cases, the conditions required to reach the observed level of Be depletion are quite extreme, which explains the very small fraction of detected Be outliers. We suggest that substantial Be depletion can be obtained in stars if they were fast rotators in the past, with high initial rotational velocities and short disc lifetimes. Our analysis suggests that rotational mixing may not be efficient enough to deplete Be in less than 10 Myr. Consequently, the detection of strongly Be-deficient stars in clusters younger than  ~10 Myr may provide a genuine signature of accretion process and the proof that some protostars may undergo many extreme bursts of accretion during their embedded phases of evolution.