Astron. Astrophys. 348, 466-474 (1999)

The orbital period of the dwarf nova HS Virginis, the revised relation and the "superhump" mass ratio distribution of SU UMa stars ^*

R.E. Mennickent  ^{**  1}, K. Matsumoto ² and J. Arenas <sup>3

1</sup> Universidad de Concepción, Departamento de Física, Casilla 4009, Concepción, Chile (rmennick@stars.cfm.udec.cl)
² Kyoto University, Faculty of Science, Department of Astronomy, Kyoto 606-8502, Japan (katsura@kusastro.kyoto-u.ac.jp)
³ Keele University, Department of Physics, Keele, Staffordshire ST5 5BG, UK (jla@astro.keele.ac.uk)

Received 17 March 1999 / Accepted 4 June 1999

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:d07692(3), although we cannot discard two aliases at 0:d07678 and 0:d07709. The Balmer lines follow the orbital period with a radial velocity semiamplitude 96 9 km 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 . A revised version of the 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 ( = 0.22 0.04) and 43 additional SU UMa stars. The 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.

Key words: stars: individual: HS Vir stars: novae, cataclysmic variables stars: fundamental parameters stars: evolution stars: binaries: general

* Based on observations obtained at ESO La Silla Observatory (ESO Proposal 61.D-0395).
** On leave in Harvard-Smithsonian Center for Astrophysics, 60 Garden St, MA 02138, Cambridge, USA

Send offprint requests to: R.E. Mennickent

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Contents

• 1. Introduction
• 2. Observations and data reduction
• 3. Results
  • 3.1. The averaged spectrum and variability
  • 3.2. The orbital period and radial velocity semiamplitude
• 4. Line radial emissivity gradients
• 5. The "superhump" mass ratio and the relation in SU UMa stars
• 6. Possible system parameters
• 7. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1999

Online publication: July 26, 1999
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