Discovery of a spectroscopic binary comprising two hot helium-rich subdwarfs^*

¹ Armagh Observatory, College Hill, Armagh BT61 9DG, N. Ireland, UK
² Dept. of Physics and Astronomy, University of Victoria, PO Box 3055, Victoria, BC V8W 3P6, Canada
³ Dept. of Physics and Astronomy, The Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA

Corresponding author: A. Ahmad, amir@star.arm.ac.uk

Received: 19 December 2003
Accepted: 17 January 2004

Abstract

Helium-rich subdwarf B (He-sdB) stars form a very small fraction of the population of hot subdwarf stars in our Galaxy. They have been found both in the field of our Galaxy as well as in globular clusters. The evolution of these rare stars has recently been the subject of much debate involving both binary and single star evolution models. We report our serendipitous discovery that the prototype – PG 1544+488 – is a binary containing two low-mass helium-rich hot subdwarfs. This discovery challenges existing evolutionary models for He-sdB stars and suggests that they may be formed through close binary evolution and following the ejection of a common envelope.