Helium Nova on a Very Massive White Dwarf -- A Light Curve Model of V445 Puppis (2000) Revised

TL;DR

This paper models the light curve of the helium nova V445 Puppis, revealing a very massive white dwarf likely to become a Type Ia supernova, and discusses the system's properties and future observational prospects.

Contribution

It provides a detailed free-free emission dominated light curve model for V445 Pup, constraining the white dwarf mass and accreted matter, and discusses its potential as a supernova progenitor.

Findings

White dwarf mass is very massive (≥1.35 M_sun).

Half of the accreted matter remains on the WD.

Distance to V445 Pup is estimated between 3.5 and 6.5 kpc.

Abstract

V445 Pup (2000) is a unique object identified as a helium nova. Color indexes during the outburst are consistent with those of free-free emission. We present a free-free emission dominated light curve model of V445 Pup on the basis of the optically thick wind theory. Our light curve fitting shows that (1) the white dwarf (WD) mass is very massive (M_WD \gtrsim 1.35 M_\sun), and (2) a half of the accreted matter remains on the WD, both of which suggest that the increasing WD mass. Therefore, V445 Pup is a strong candidate of Type Ia supernova progenitor. The estimated distance to V445 Pup is now consistent with the recent observational suggestions, 3.5 < d < 6.5 kpc. A helium star companion is consistent with the brightness of m_v=14.5 mag just before the outburst, if it is a little bit evolved hot (\log T (K) \gtrsim 4.5) star with the mass of M_He \gtrsim 0.8 M_\sun. We then emphasize importance of observations in the near future quiescent phase after the thick circumstellar dust dissipates away, especially its color and magnitude to specify the nature of the companion star. We have also calculated helium ignition masses for helium shell flashes against various helium accretion rates and discussed the recurrence period of helium novae.