EDP Sciences
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Volume 418, Number 1, April IV 2004
Page(s) 265 - 270
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361:20035591

A&A 418, 265-270 (2004)
DOI: 10.1051/0004-6361:20035591

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

B. T. Gänsicke1, 2, S. Araujo-Betancor1, H.-J. Hagen3, E. T. Harlaftis4, S. Kitsionas5, S. Dreizler6 and D. Engels3

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

(Received 29 October 2003 / Accepted 15 January 2004)

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 $\mbox{${\rm H\alpha}$ }$ radial velocity variations measured from time-resolved spectroscopy determine the orbital period to be $\mbox{$P_{\rm orb}$ }=178.10$  $\pm$ 0.08 min. The optical spectrum of HS 2237+8154 is well described by a combination of a $\mbox{$T_{{\rm eff}}$ }=11\,500$  $\pm$ 1500 K white dwarf (assuming $\log g=8$) and a dM 3.5  $\pm$ 0.5 secondary star. The distance implied from the flux scaling factors of both stellar components is d=105  $\pm$ 25 pc. Combining the constraints obtained from the radial velocity of the secondary and from the ellipsoidal modulation, we derive a binary inclination of $i\simeq50^{\circ}{-}70^{\circ}$ and stellar masses of $\mbox{$M_{{\rm wd}}$ }=0.47{-}0.67$  $M_{\odot}$ and $\mbox{$M_{{\rm sec}}$ }=0.2{-}0.4$  $M_{\odot}$. 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.

Key words: stars: binaries: close -- stars: individual: HS 2237+8154 -- stars: novae, cataclysmic variables

Offprint request: B. T. Gänsicke, Boris.Gaensicke@warwick.ac.uk

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