In this paper we present the results of time-resolved spectroscopy in the near-infrared of five cataclysmic variables: U Gem, SS Aur, BD Pav, DO Dra and CN Ori. The spectral region observed was chosen to cover the Na 1 doublet at λ8190 Å which is strong in late-type dwarfs. Radial-velocity curves were measured for the secondary stars and values for Kabs determined for each object. For DO Dra an improved orbital period of 3.969±0.003 hr was derived.U Gem and SS Aur showed significant apparent eccentricities of 0.027±0.012 and 0.17±0.07, respectively. This distortion of the radial-velocity curve is probably caused by line quenching due to irradiation of the secondary, or contamination of the spectrum by emission from the disc, or a combination of the two. For U Gem the apparent eccentricity was used to correct the observed Kabs for these effects. Mass ranges were derived for all the objects. For U Gem, which has the most closely constrained result, the secondary mass is larger than predicted using main-sequence mass-period relations. Spectral-type estimates for U Gem and DO Dra are also later than expected if the secondary obeys an empirical main-sequence mass-radius relation. It is concluded that the assumption of main-sequence status for the secondary star should be used with caution.
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- October 1990