Research Note

Lithium enhancement in X-ray binaries due to stellar rotation

¹ Astronomical Institute “Anton Pannekoek”, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands e-mail: tjm@science.uva.nl
² Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02139, USA
³ SRON, National Institute for Space Research, 3584 CA, Utrecht, The Netherlands
⁴ Department of Physics and Astronomy, McMaster University, Hamilton, Ontario, L8S 4M1, Canada

Received: 27 December 2004
Accepted: 9 March 2005

Abstract

We discuss the high lithium abundances in the secondary stars of X-ray binaries. We show that no lithium production in these stars is necessary, and that the abundances can be explained simply due to the tidally locked rotation of the stars, which lead naturally to slower lithium destruction rates. The differences in abundances of CVs' secondaries from those of LMXBs had previously been put forth as evidence that the compact object was related to the lithium abundance, but this scenario also accounts for the lower lithium abundances in the secondary stars in cataclysmic variable systems (CVs) than in low mass X-ray binaries (LMXBs), since these stars have typically lived much longer before becoming tidally locked short period systems. We point out that if this scenario is correct, then the globular cluster X-ray binaries' donor stars should, as a class, show less lithium enhancement relative to other stars of the same spectral type in the clusters than the field X-ray binaries donor stars show.