The Long-Term Secular Mass Accretion Rate of the Recurrent Nova T Pyxidis

TL;DR

This study uses ultraviolet spectroscopy and accretion disk modeling to estimate the long-term mass accretion rate of T Pyxidis, revealing a lower rate than previously thought, with implications for the white dwarf's mass evolution.

Contribution

It provides updated measurements of the mass accretion rate in T Pyxidis using new UV data and improved models, considering Gaia distance revisions and their impact on accretion estimates.

Findings

Mass accretion rate is around 1e-7 Solar masses per year with Gaia distance.

The white dwarf's mass may be increasing or stable depending on accretion rate and observational constraints.

Predicted soft X-ray or EUV emission from the accretion disk's hot inner region.

Abstract

We present Hubble Space Telescope ultraviolet spectroscopy of the recurrent nova T Pyxidis obtained more than 5 years after its 2011 outburst indicating that the system might not have yet reached its deep quiescent state. The ultraviolet data exhibit a 20% decline in the continuum flux from the pre-outburst deep quiescence state to the post-outburst near quiescent state. We suggest that a decline across each recurring nova eruption might help explain the proposed 2mag steady decline of the system since 1866. Using an improved version of our accretion disk model as well as International Ultraviolet Explorer ultraviolet and optical data, and the 4.8 kpc distance, we corroborate our previous findings that the quiescent mass accretion rate in T Pyx is of the order of 1e-6 Solar mass per year. Such a large mass accretion rate would imply that the mass of the white dwarf is increasing with time. However, with the just-release Gaia DR 2 distance of 3.3 kpc (after submission of the first version of this manuscript), we find a mass accretion of the order of 1e-7 Solar mass per year. Our results predict powerful soft X-ray or extreme ultraviolet emission from the hot inner region of the high accretion rate disk. Using constraining X-ray observations and assuming the accretion disk doesn't depart too much from the standard model, we are left with two possible scenarios. The disk either emits mainly extreme ultraviolet radiation which, at a distance of a few kpc, is completely absorbed by the interstellar medium, or the hot inner disk, emitting soft X-rays, is masked by the bulging disk seen at a higher inclination.