6 Summary

In this paper we present the results of non-simultaneous time-resolved photometric and spectroscopic observations of the little-studied dwarf nova FS Aur in quiescence. We have obtained the following results:

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The spectrum of FS Aur shows strong and broad emission lines of hydrogen and HeI, and of weaker HeII $\lambda4686$ and CIII/NIII blend, similar to other quiescent dwarf novae.

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All emission lines in the spectrum of FS Aur are single-peaked, however their form varies with orbital phase.

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Absorption lines from a late-type secondary are not detected.

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From the radial velocity measurements of the hydrogen lines H$\beta$ and H$\gamma$ we have determined a most probable orbital period $P=0\hbox{$.\!\!^{\rm d}$ }059 \pm 0\hbox{$.\!\!^{\rm d}$ }002$. This period agrees well with the 0 $.\!\!^{\rm d}$0595 $\pm$ 0 $.\!\!^{\rm d}$0001 estimate by TPST. On the other hand, the period of photometric modulations is longer than the spectroscopic period and can be estimated as 3 hours. Longer time coverage during a single night is needed to resolve this problem.

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Using the semi-amplitude of the radial velocities, obtained from measurements of hydrogen and helium lines, and some empirical and theoretical relations we limited the basic parameters of the system: the mass ratio $q \geq 0.22$, the primary mass $M_{1}=0.34{-}0.46~M_{\odot}$, the secondary mass $M_{2} \leq 0.1~M_{\odot}$, and the inclination angle $i=51^{\circ }{-}65^{\circ}$.

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Doppler tomography has shown at least two bright regions in the accretion disk of FS Aur. The first, brighter spot is located at a phase of about 0.6. The second spot is located opposite the first one and occupies an extensive area at phases about 0.85-1.15.

Acknowledgements

I am grateful to Oksana van den Berg for contributing to a improved first version of this paper. I would like to thank the firm VEM (Izhevsk, Russia) and Konstantin Ishmuratov personally for the financial support rendered to me in the preparation of this paper. Thanks also to Alexander Khlebov for the computer and technical support. I acknowledge the referee Jet Katgert for detailed reading of the manuscript, improving the language of the manuscript, and useful suggestions concerning the final version.