HS 2237+8154: On the onset of mass transfer or entering the period gap?^*

¹ School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, UK
² Department of Physics, University of Warwick, Coventry CV4 7AL, UK
³ Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
⁴ Institute of Space Applications and Remote Sensing, National Observatory of Athens, PO Box 20048, Athens 11810, Greece
⁵ Institute of Astronomy and Astrophysics, National Observatory of Athens, PO Box 20048, Athens 11810, Greece
⁶ Universitäts-Sternwarte, Geismarlandstr. 11, 37083 Göttingen, Germany

Corresponding author: B. T. Gänsicke, Boris.Gaensicke@warwick.ac.uk

Received: 29 October 2003
Accepted: 15 January 2004

Abstract

We report follow-up observations of a new white dwarf/red dwarf binary HS 2237+8154, identified as a blue variable star from the Hamburg Quasar Survey. Ellipsoidal modulation observed in the R band as well as the  radial velocity variations measured from time-resolved spectroscopy determine the orbital period to be P_orb ± 0.08 min. The optical spectrum of HS 2237+8154 is well described by a combination of a  ± 1500 K white dwarf (assuming ) and a dM 3.5 ± 0.5 secondary star. The distance implied from the flux scaling factors of both stellar components is  ± 25 pc. Combining the constraints obtained from the radial velocity of the secondary and from the ellipsoidal modulation, we derive a binary inclination of and stellar masses of   and  . All observations imply that the secondary star must be nearly Roche-lobe filling. Consequently, HS 2237+8154 may be either a pre-cataclysmic variable close to the start of mass transfer, or – considering its orbital period – a cataclysmic variable that terminated mass transfer and entered the period gap, or a hibernating nova.