HS 0907+1902: a new 4.2 hr eclipsing dwarf nova

We report on follow-up spectroscopy and photometry of the cataclysmic varia ble candidate HS 0907+1902 selected from the Hamburg Quasar Survey. B, V, a nd R photometry obtained during the first observed outburst of HS 0907+1902 (V approximate to 13) reveals deep eclipses (Delta V approximate to 2.1 - 2.8) and an orbital period P-orb = 4.2 h with the eclipse depth decreasing to the red. The outburst eclipse profiles are symmetric, indicating an axis ymmetrical brightness distribution in the accretion disc. We derive an incl ination i approximate to 73 degrees - 79 degrees from the eclipse duration. The quiescent spectrum obtained with the Hobby-Eberly Telescope shows doub le peaked emission lines of H I, He I and Fe I,II and clearly identifies th e system as a dwarf nova. Absorption features of the secondary star are det ected at red wavelengths from which a spectral class M3 +/- 1.5 and a dista nce of d = 320 +/- 100 pc are derived.