Abstract
ABSTRACTDV Ursae Majoris is a deeply eclipsing dwarf nova which shows very powerful superhumps when it attains superoutburst. We report detailed observations of the 1997 and 1999 eruptions. Some of the results reproduce what has been learned from other eclipsing dwarf novae: that the disk becomes very large in outburst, that superhumps develop in a few days, and that superhumps remain strong even after the disk has shrunk by more than 30%. The mean superhump period was 0.08870(8) day, but in both eruptions the period decreased with P˙ ≈ -6 × 10-5. Globally distributed coverage of the 1997 eruption revealed two other interesting features: a transient strong modulation at the orbital period at the peak of eruption, and intricate fine structure in the harmonics of the main superhump signal. In particular, we found that the second harmonic occurred not at 3ω−3Ω as expected (where ω and Ω are, respectively, the orbital and “precession” frequencies), but at 3ω−2Ω and 3ω−Ω. The strong orbital modulation may have arisen from enhanced mass transfer from the secondary.We also report photometry at quiescence, which separates the luminous contributions of the white dwarf, accretion disk, and secondary star. We estimate a distance of 350 ± 120 pc. Analysis of the eclipses suggests i = 84.°0 ± 0.°8,q = 0.155 ± 0.015,M2 = 0.14 ± 0.02 M⊙,M1 = 0.90 ± 0.13 M⊙.
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