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

Abstract

Abstract We observed the long-term behavior of the helium dwarf nova V803 Cen, and clarified the existence of at least two distinct states (a state with 77-d supercycles and a standstill-like state) that interchangeably appeared with a time-scale of 1–2 yr. We also conducted a time-resolved CCD photometry campaign during a bright outburst in 2003 June. The overall appearance of the outburst closely resembles that of the late stage of the 2001 outburst of WZ Sge, consisting of the initial peak stage (superoutburst plateau), the dip, and the oscillating (rebrightening) states. During the initial peak stage, we detected a large-amplitude superhump-type variation with a period of $0.018686(4) \,\mathrm{d} = 1614.5(4) \,\mathrm{s}$, and during the oscillation stage we detected variations with a period of $0.018728(2) \,\mathrm{d} = 1618.1(2) \,\mathrm{s}$. We consider that the former period better represents the superhump period of this system, and the latter periodicity may be better interpreted as arising from late superhumps. The overall picture of the V803 Cen outburst resembles that of a WZ Sge-type outburst, but apparently with a higher mass-transfer rate than that in hydrogen-rich WZ Sge-type stars. We suggest that this behavior may be either the result of difficulty in maintaining the hot state in a helium disk, or the effect of an extremely low tidal torque resulting from the extreme mass ratio.