The precataclysmic variable GD 245

A combined photometric/spectroscopic study has been carried out of the evolved binary GD 245. The system is shown to consist of a DA2 white dwarf plus M3-5 secondary in a 4.17 h orbit. From model fitting to the white dwarf spectral features, the primary star is found to have log g = 7.77±0.02 and T_eff=22170 K, leading to M₁(g)=0.48script M sign_⊙ and R₁=0.0150R_⊙. Radial velocity analysis of the double-lined system implies M₂=0.22script M sign_⊙. The distance is computed to be 61 pc and the orbital inclination is i≈69°. These parameters are consistent with the companion being a main-sequence object, in which case T_eff=3560 K, R₂=0.27R_⊙, and the binary just escapes being an eclipsing system. A rich spectrum of emission lines phased in strength and radial velocity with the orbital motion is testimony to irradiation of a corotating secondary star by the white dwarf. However, the strength of this spectral component exceeds the intercepted Lyman continuum from the white dwarf, implying that alternate heating mechanisms are important. The companion underfills its Roche lobe by less than 25% in radius, and for current estimates of the angular momentum loss rate in close binaries will require less than 10⁸ yr to evolve into contact. At the inception of mass transfer, the cataclysmic variable GD 245 will appear as one of the rare objects in the 2-3 h orbital period gap.