Spectroscopic Study of SU UMa - type Dwarf Nova YZ Cnc during its 2002 Superoutburst

We report time-resolved spectroscopic observations of the SU Ursae Majoris dwarf nova, YZ Cnc, for 2 nights over 11 hrs during its 2002 January superoutburst. The spectra only show absorption-line profiles in the first day. But the lines display blue and red troughs, with “W” profiles in the second day. The radial velocity curve of the absorption troughs and emission peaks of Hβ has an amplitude of 49± 10 km s and a phase offset of −0.07 ± 0.04, which are very similar to those measured in quiescence; however, the γ velocity deviates strongly from the systemic velocity measured in quiescence, showing variation of the order of ±60 km s. And large shifts of ∼70 km s and ∼0.09, for the orbital-averaged velocity and phase respectively, are also found in our observations. All these phenomena can be well explained with a precession of an eccentric disk and we conclude that these phenomena are the characteristic products of an eccentric accretion disk.