HS 0907 + 1902 : a new 4 . 2 hr eclipsing dwarf nova

We report on follow-up spectroscopy and photometry of the cataclysmic variable candidate HS 0907+1902 selected from the Hamburg Quasar Survey. B, V , and R photometry obtained during the first observed outburst of HS 0907+1902 (V ≈ 13) reveals deep eclipses (∆V ≈ 2.1 − 2.8) and an orbital period Porb = 4.2 h with the eclipse depth decreasing to the red. The outburst eclipse profiles are symmetric, indicating an axisymmetrical brightness distribution in the accretion disc. We derive an inclination i ≈ 73◦ − 79◦ from the eclipse duration. The quiescent spectrum obtained with the Hobby-Eberly Telescope shows double peaked emission lines of H I, He I and Fe I,II and clearly identifies the system as a dwarf nova. Absorption features of the secondary star are detected at red wavelengths from which a spectral class M3± 1.5 and a distance of d = 320 ± 100 pc are derived.