The secrets of T Pyxidis II. A recurrent nova that will not become a SN Ia

TL;DR

This study provides detailed measurements of T Pyxidis's accretion and eruption parameters, confirming thermonuclear runaway theory, and shows the white dwarf is unlikely to reach the Chandrasekhar limit, thus not becoming a Type Ia supernova.

Contribution

It offers the first direct estimate of accreted mass and compares it with ignition mass, confirming key aspects of nova theory and challenging previous assumptions about white dwarf growth in recurrent novae.

Findings

Accreted mass matches ignition mass at ~5×10⁻⁷ M☉ for M₁≈1.37 M☉

T Pyx ejects more material than it accretes, preventing growth to Chandrasekhar limit

UV and X-ray data exclude T Pyx as a supersoft X-ray source

Abstract

By various methods, we obtained L$_{disk}$ $\sim$ 70 L$_{\odot}$ and $\dot{M}$ $\sim$1.1 $\times$ 10$^{-8}$ M$_{\odot}$yr$^{-1}$. These values were about twice as high in the pre-1966-outburst epoch. This allowed the first direct estimate of the total mass accreted before outburst, M$_{accr}$=$\dot{M}_{pre-OB}$ $\cdot \Delta$t, and its comparison with the critical ignition mass M$_{ign}$. We found M$_{accr}$ and M$_{ign}$ to be in perfect agreement (with a value close to 5 $\times$ 10$^{-7}$M$_{\odot}$) for M$_1$ $\sim$ 1.37 M$_{\odot}$, which provides a confirmation of the thermonuclear runaway theory. The comparison of the observed parameters of the eruption phase, with the corresponding values in the grid of models by Yaron and collaborators, provides satisfactory agreement for values of M$_1$ close to 1.35 M$_{\odot}$ and log$\dot{M}$ between -8.0 and -7.0, but the observed value of the decay time t$_3$ is higher than expected. The long duration of the optically thick phase during the recorded outbursts of T Pyx, a spectroscopic behavior typical of classical novae, and the persistence of P Cyg profiles, constrains the ejected mass M$_{ign}$ to within 10$^{-5}$ - 10$^{-4}$ M$_{\odot}$. Therefore, T Pyx ejects far more material than it has accreted, and the mass of the white dwarf will not increase to the Chandrasekhar limit as generally believed in recurrent novae. A detailed study based on the UV data excludes the possibility that T Pyx belongs to the class of the supersoft X-ray sources, as has been postulated. XMM-NEWTON observations have revealed a weak, hard source and confirmed this interpretation.