2004A&A...418..265G

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 Hα radial velocity variations measured from time-resolved spectroscopy determine the orbital period to be P_orb=178.10±0.08min. The optical spectrum of HS 2237+8154 is well described by a combination of a T_eff=11500±1500K white dwarf (assuming logg=8) and a dM 3.5±0.5 secondary star. The distance implied from the flux scaling factors of both stellar components is d=105±25pc. Combining the constraints obtained from the radial velocity of the secondary and from the ellipsoidal modulation, we derive a binary inclination of i≃50°-70° and stellar masses of M_wd=0.47-0.67M_☉ and M_sec=0.2-0.4M_☉. 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.