2003A&A...409..647B

The first time-resolved spectroscopic observations of the dwarf nova AT Ara are presented. The system is a double lined spectroscopic binary. Thus, radial velocity curves of both, emission lines from the accretion disk (in this particular case of Hα) and of the secondary star can be measured. An orbital period of 0.37551 days is derived, placing AT Ara among the cataclysmic variables with the longest revolution periods. The RV-amplitudes yield a mass ratio of q=M₂/M₁=0.79±0.09. The spectral type of the secondary star is K2. AT Ara has an intermediate orbital inclination of 38°±5°. The secondary star has a mass and a radius of M₂=0.42±0.10M_☉ and R₂=0.84±0.19R_☉, respectively. It is thus significantly larger than a main sequence star of the same mass. Evolutionary calculations of cataclysmic variables suggest that the secondary is nuclearly evolved to a certain degree. The distance to AT Ara is estimated to be of the order of 600pc.