* Astronomy

Title: CI Aql: a Type Ia supernova progenitor?
Authors: Dave Sahman, Vik Dhillon, Tom Marsh, Sarah Moll, Tim Thoroughgood, Chris Watson, Stuart Littlefair

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 solar masses (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 solar masses and the mass of the secondary star to be 2.32 ± 0.19 solar masses. We estimate the radius of the secondary to be 2.07 ± 0.06 solar radii, 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.

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