V803 Centauri: Helium Dwarf Nova Mimicking a WZ Sge-Type Superoutburst

We observed long-term behavior of the helium dwarf nova V803 Cen, andclarified the existence of at least two distinct states (state with 77-dsupercycles and standstill-like state) which interchangeably appeared with atime-scale of 1--2 yr. We also conducted a time-resolved CCD photometrycampaign during the bright outburst in 2003 June. The overall appearance of theoutburst closely resemble that of the late stage of the 2001 outburst of WZSge, consisting of the initial peak stage (superoutburst plateau), the dip, andthe oscillating (rebrightening) states. During the initial peak stage, wedetected large-amplitude superhump-type variation with a period of 0.018686(4)d = 1614.5(4) s, and during the oscillation stage, we detected variations witha period of 0.018728(2) d = 1618.1(2) s. We consider that the former periodbetter represents the superhump period of this system, and the latterperiodicity may be better interpreted as arising from late superhumps. Theoverall picture of the V803 Cen outburst resembles that of a WZ Sge-typeoutburst, but apparently with a higher mass-transfer rate than in hydrogen-richWZ Sge-type stars. We suggest that this behavior may be either the result ofdifficulty in maintaining the hot state in a helium disk, or the effect of anextremely low tidal torque resulting from the extreme mass ratio.Comment: 13 pages, 11 figures, to appear in PAS