Time resolved spectroscopy and photometry of the dwarf nova FS Aurigae in quiescence ⋆

We present results of non-simultaneous time resolved photometric and spectroscopic observations of little-studied dwarf nova FS Aur in quiescence. The spectrum of FS Aur shows strong and broad emission lines of hydrogen and He I, and of weaker He II λ4686 and C III/N III blend, similar to other quiescent dwarf novae. All emission lines are single-peaked, however their form varies with an orbital phase. Absorption lines from a late-type secondary are not detected. From the radial velocity measurements of the hydrogen lines H β and Hγ we determined a most probable orbital period P=0. d 059 ± 0. d 002. This period agrees well with the 0. d 0595 ± 0. d 0001 estimate by TPST. On the other hand, the period of photometric modulations is longer than spectroscopic period and can be appreciated at least as 3 hours. Longer timescale coverage during a single night is needed to resolve this problem. Using semi-amplitude of the radial velocities, obtained from measurements of hydrogen and helium lines, and some empirical and theoretical relations we limited basic parameters of the system: a mass ratio q ≥ 0.22, a primary mass M1 = 0.34 ÷ 0.46M ⊙ , a secondary mass M2 ≤ 0.1M ⊙ , and an inclination angle i = 51 • ÷ 65 •. Doppler tomography have shown at least two bright region in accretion disk of FS Aur. The first more bright spot is located at phase about 0.6. The second spot is located opposite to the first one and occupies an extensive area at phases about 0.85 ÷ 1.15.