V445 Puppis: Helium Nova on a Massive White Dwarf

The 2000 outburst of V445 Puppis shows unique properties, such as absence ofhydrogen, enrichment of helium and carbon, slow development of the light curvewith a small amplitude that does not resemble any classical novae. This objecthas been suggested to be the first example of helium novae. We calculatetheoretical light curves of helium novae and reproduce the observational lightcurve of V445 Pup. Modeling indicates a very massive white dwarf (WD), moremassive than 1.3 Msun. The companion star is possibly either a helium star or ahelium-rich main-sequence star. We estimate the ignition mass as several times10^{-5} Msun, the corresponding helium accretion rate as several times 10^{-7}Msun yr^{-1}, and the recurrence period as several tens of years. These valuessuggest that the WD is growing in mass and ends up either a Type Ia supernovaor an accretion induced collapse to a neutron star.Comment: 6 pages including 3 figures, to appear in ApJ