Photometry and Spectroscopy of KS Ursae Majoris during Superoutburst

We report photometric and spectroscopic observations of the SU UMa-type dwarfnovae, KS Ursae Majoris, during its 2003 February superoutburst. Modulationswith a period of $0.07017\pm0.00021$ day, which is 3.3% larger than the orbitalperiod, have been found during the superoutburst and may be positivesuperhumps. A maximum trough-to-peak amplitude of around 0.3 magnitude isdetermined for this superhump. The spectra show broad, absorption-line profiles. The lines display blue andred troughs which alternate in depth. The radial velocity curve of theabsorption wings of H$\beta$ has an amplitude of $40\pm11$ km s$^{-1}$ and aphase offset of $0.12\pm0.03$. The $\gamma$ velocity of the binary is $3\pm9$km s$^{-1}$ and varies on an order of 50 km s$^{-1}$ from day to day. Fromanother clear evidence for a precessing eccentric disk, we obtain a solution toan eccentric outer disk consistent with theoretical works, which demonstratesthe validity of the relation between superhumps and tidal effects. The innerpart of the disk is also eccentric as evidenced by asymmetric and symmetricwings in the lines. Therefore, the whole disk is eccentric and the variation of$\gamma$ velocity and the evolutionary asymmetric line profiles could becriterions for an precessing eccentric accretion disk.Comment: 12 pages, 8 figures, accpeted for publication in A