We report photometry of the dwarf nova DI Ursae Majoris during 1997-1998. The star shows an orbital light curve at quiescence with a period of 0.054564(1) days. During superoutburst, it flashes superhumps with a period of 0.05529(5) days. The superhump period excess of 1.3% is quite low among cataclysmic variables, suggesting a weak perturbation on the accretion disk and therefore a secondary of very low mass. But other stars of low period excess are rare eruptors, whereas DI UMa is extremely active with normal outbursts every 8 days and superoutbursts every 30-45 days. This is puzzling. We speculate that the binary really does have a secondary of anomalously low mass but is presently in a high state of a mass-transfer cycle.
|Number of pages
|Publications of the Astronomical Society of the Pacific
|Published - Oct 1999