Discovery of a bright eclipsing cataclysmic variable

Aims. We report on the discovery of J0644+3344, a bright deeply eclipsing cataclysmic variable (CV) binary. Methods. Optical photometric and spectroscopic observations were obtained to determine the nature and characteristics of this CV. Results. Spectral signatures of both binary components and an accretion disk can be seen at optical wavelengths. The optical spectrum shows broad H I, He I, and He II accretion disk emission lines with deep narrow absorption components from H I, He I, Mg II and Ca II. The absorption lines are seen throughout the orbital period, disappearing only during primary eclipse. These absorption lines are either the the result of an optically-thick inner accretion disk or from the photosphere of the primary star. Radial velocity measurements show that the H I, He I, and Mg II absorption lines phase with the the primary star, while weak absorption features in the continuum, between Hα and Hβ, phase with the secondary star. Radial velocity solutions give a 150±4 km s−1 semi-amplitude for the primary star and 192.8±5.6 km s−1 for the secondary, resulting in a primary to secondary mass ratio of q=1.285. The individual stellar masses are 0.63−0.69 M⊙ for the primary and 0.49−0.54 M⊙ for the secondary, with the uncertainty largely due to the inclination. Conclusions. The bright eclipsing nature of this binary has helped provide masses for both components with an accuracy rarely achieved for cataclysmic variables. This binary most closely resembles a nova-like UX UMa or SW Sex type of cataclysmic variable. J0644+3344, however, has a longer orbital period than most UX UMa or SW Sex stars. Assuming an evolution toward shorter orbital periods, J0644+3344 is therefore likely to be a young interacting binary. The secondary star is consistent with the size and spectral type of a K8 star, but has the mass of a M0.