Abstract

A spectroscopic study of the SU UMa star HS Vir is presented. From the analysis of the radial velocities of the H? emission line the most likely orbital period is 0 d.07692(3), although we cannot discard two aliases at 0 d.07678 and 0 d.07709. The Balmer lines follow the orbital period with a radial velocity semiamplitude K = 96 ± 9km s -1, but the He I ? 5875 emission line shows a double wave during the orbital cycle. We found that the mean Balmer, He I and He II 4686 lines can be roughly modeled with a disk radial emissivity ? r -2. A revised version of the P o - P s relation for SU UMa stars is also given, which is relevant for discriminating between ± 1 c/d aliases of the orbital period. We calculated the mass ratio, derived from the tidal resonance model, of HS Vir (q sh = 0.22 ± 0.04) and 43 additional SU UMa stars. The q sh distribution has a roughly gaussian shape with a mean 0.14, in sharp contrast with the orbital period distribution. Finally, a discussion of the possible stellar masses and inclination of HS Vir is given. We observe that the mass ratio derived from the dynamic solution is in disagreement with that derived from the tidal resonance model. This fact probably indicates that K does not represent the white dwarf binary motion.