CI Aql: a Type Ia supernova progenitor?

TL;DR

This study measures the masses of the white dwarf and companion star in the recurrent nova CI Aql, suggesting it is a potential Type Ia supernova progenitor with rapid evolution towards explosion.

Contribution

First dynamical mass estimate of CI Aql's components, indicating its possible future as a Type Ia supernova within 10 million years.

Findings

White dwarf mass is 1.00 +/- 0.14 Msolar.

Secondary star mass is 2.32 +/- 0.19 Msolar.

System may evolve into a supernova within 10 Myr.

Abstract

If recurrent novae are progenitors of Type Ia supernovae, their white dwarfs must have masses close to the Chandrasekhar limit. The most reliable means of determining white dwarf masses in recurrent novae is dynamically, via radial-velocity and rotational-broadening measurements of the companion star. Such measurements require the system to be both eclipsing and to show absorption features from the secondary star. Prior to the work reported here, the only dynamical mass estimate of a recurrent nova was for U Sco, which has a white dwarf mass of 1.55 +/- 0.24 Msolar (Thoroughgood et al. 2001). We present new time-resolved, intermediate-resolution spectroscopy of the eclipsing recurrent nova CI Aquilae (CI Aql) during quiescence. We find the mass of the white dwarf to be 1.00 +/- 0.14 Msolar and the mass of the secondary star to be 2.32 +/- 0.19 Msolar. We estimate the radius of the secondary to be 2.07 +/- 0.06 Rsolar, implying that it is a slightly-evolved early A-type star. The high mass ratio of q = 2.35 +/- 0.24 and the high secondary-star mass implies that the mass transfer occurs on a thermal timescale. We suggest that CI Aql is rapidly evolving into a supersoft X-ray source, and ultimately may explode as a Type Ia supernova within 10 Myr.