The Unique Helium Nova V445 Puppis Ejected $\gg$0.001 M$_{\odot}$ in the Year 2000 and Will Not Become a Type Ia Supernova

TL;DR

This study of the helium nova V445 Puppis reveals it ejects more mass than it accretes, preventing it from becoming a Type Ia supernova, and provides detailed orbital and mass loss measurements.

Contribution

It offers the first detailed orbital period and mass ejection measurements for V445 Puppis, demonstrating it cannot evolve into a Type Ia supernova.

Findings

Ejected mass in 2000 was much greater than accreted mass.

White dwarf is losing mass over cycles, not gaining.

Helium novae are not progenitors of Type Ia supernovae.

Abstract

V445 Puppis is the only known example of a helium nova, where a layer of helium-rich gas accretes onto the surface of a white dwarf in a cataclysmic variable, with runaway helium burning making for the nova event. Speculatively, helium nova can provide one path to produce a Type Ia supernova (SNIa), within the larger framework of single-degenerate models. Relatively little has been known about V445 Pup, with this work reporting the discovery of the orbital period near 1.87 days. The companion star is 2.65$\pm$0.35 R$_{\odot}$ in radius as an evolved giant star stripped of its outer hydrogen envelope. The orbital period immediately before the 2000 eruption was $P_{\rm pre}$=1.871843$\pm$0.000014 days, with a steady period change of (-0.17$\pm$0.06)$\times$10$^{-8}$ from 1896--1995. The period immediately after the nova eruption was $P_{\rm post}$=1.873593$\pm$0.000034 days, with a $\dot{P}$ of ($-$4.7$\pm$0.5)$\times$10$^{-8}$. The fractional orbital period change ($\Delta P/P$) is $+$935$\pm$27 ppm. This restricts the mass of the gases ejected in the nova eruption to be $\gg$0.001M$_{\odot}$, and much greater than the mass accreted to trigger the nova. So the white dwarf is losing mass over each eruption cycle, and will not become a SNIa. Further, for V445 Pup and helium novae in general, I collect observations from 136 normal SNIa, for which any giant or sub-giant companion star would have been detected, yet zero companions are found. This is an independent proof that V445 Pup and helium novae are not SNIa progenitors.