Discovery of a bright eclipsing cataclysmic variable

¹ Institut d'Astrophysique de Paris, CNRS/UPMC, 98bis boulevard Arago, 75014 Paris, France e-mail: sing@iap.fr
² Lunar and Planetary Laboratory, Sonett Bld., University of Arizona, Tucson, AZ 85721, USA e-mail: holberg@argus.lpl.arizona.edu
³ Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA e-mail: [bgreen;gschmidt]@as.arizona.edu
⁴ WIYN Observatory & NOAO, PO Box 26732, 950 N. Cherry Ave., Tucson, AZ 85726-6732, USA e-mail: howell@noao.edu
⁵ Carnegie Institution of Washington, Dept. of Terrestrial Magnetism, 5241 Broad Branch Road NW, Washington, DC 20015, USA e-mail: mercedes@dtm.ciw.edu
⁶ Department of Physics and Astronomy, University of Georgia, Athens, GA 30602-2451, USA e-mail: jss@hal.physast.uga.edu

Received: 6 June 2007
Accepted: 3 August 2007

Abstract

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 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 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 for the primary and 0.49-0.54 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 CVs. This binary most closely resembles a nova-like UX UMa or SW Sex type of CV. 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.