No abstract

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No abstract

We report time-resolved spectroscopic observations of the recently discovered dwarf nova, IY Ursae Majoris, over 2 days during its 2000 January superoutburst. The spectra show prominent, broad, and double-peaked emission lines of Ha, Hb, Hg, Hd, and He ii and weaker He i lines. The radial velocity curve of the peaks of Ha and Hb has an amplitude of km s Ϫ1 and a phase offset of . From clear evidence for a 93 ‫ע‬ 7 0.12 ‫ע‬ 0.03 precessing 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 g velocity of the binary is derived as Ϫ km s Ϫ1 according to the solution. The inner part of the disk is also eccentric as evidenced by 4 ‫ע‬ 32 asymmetric wings in the lines. Therefore, the whole disk is eccentric. Finally, we find that a simple model can explain all asymmetric features of the emission lines.