Photometry and Spectroscopy of KS Ursae Majoris during Superoutburst

We report photometric and spectroscopic observations of the SU UMa - type dwarf nova KS Ursae Majoris during its 2003 February superoutburst. Modulations with a period of 0. 07017 +/- 0. 00021 days, which is 3.3% larger than the orbital period, have been found during the superoutburst and may be positive superhumps. A maximum trough- to-peak amplitude of around 0.3 mag is determined for this superhump. The spectra show broad absorption- line profiles. The lines display blue and red troughs that alternate in depth. The radial velocity curve of the absorption wings of H beta has an amplitude of 40 +/- 11 km s (-1) and a phase offset of 0. 12 +/- 0. 03. The gamma- velocity of the binary is 3 +/- 9 km s (-1) and varies on the order of 50 km s (-1) from day to day. From other clear evidence for a precessing eccentric disk, we obtain a solution to an eccentric outer disk consistent with theoretical works, which demonstrates the validity of the relation between superhumps and tidal effects. The inner part of the disk is also eccentric, as evidenced by asymmetric and symmetric wings in the lines. Therefore, the whole disk is eccentric, and the variation of the gamma- velocity and the evolutionary asymmetric line profiles could be criteria for a precessing eccentric accretion disk.