The discovery of a massive white dwarf in the peculiar binary system HD 49798/RX J0648.0-4418

TL;DR

This paper reports the discovery of a rapidly rotating, massive white dwarf in the binary system HD 49798/RX J0648.0-4418, with implications for supernova progenitors.

Contribution

It provides the first precise mass measurement of a white dwarf in this peculiar binary system using X-ray timing and eclipse data.

Findings

White dwarf mass is 1.28 solar masses.

White dwarf exhibits 13-second pulsations.

System may evolve into a Type Ia supernova.

Abstract

An XMM-Mewton observation performed in May 2008 has confirmed that the 13 seconds pulsations in the X-ray binary HD 49798/RX J0648.0-4418 are due to a rapidly rotating white dwarf. From the pulse time delays induced by the 1.55 days orbital motion, and the system's inclination, constrained by the duration of the X-ray eclipse discovered in this observation, we could derive a mass of 1.28+/-0.05 M_sun for the white dwarf. The future evolution of this post common envelope binary system will likely involve a new phase of mass accretion through Roche-lobe overflow that could drive the already massive white dwarf above the Chandrasekhar limit and produce a Type Ia supernova.