ASAS-SN 13cl : A Newly-Discovered Cataclysmic Binary with an Anomalously Warm Secondary

TL;DR

This paper reports the discovery of a cataclysmic variable star, ASAS-SN 13cl, with an unusually warm secondary star of spectral type K4, which is atypical for its orbital period and suggests a different evolutionary history.

Contribution

It presents the identification of a CV with a warm secondary star, indicating a possible evolutionary pathway involving prior nuclear evolution of the secondary.

Findings

Secondary star has spectral type K4, warmer than typical for its orbital period.

Orbital period is 4.86 hours with a radial velocity semi-amplitude of 246 km/s.

The system shows ellipsoidal variations and a grazing eclipse.

Abstract

The spectrum of the recently discovered cataclysmic variable star (CV) ASAS-SN 13cl shows that a secondary star with spectral type K4 (+- 2 subclasses) contributes roughly half the optical light. The radial velocities of the secondary are modulated on an orbital period P_orb = 4.86 hr with a velocity semiamplitude K = 246 +- 9 km/s, and the light curve shows ellipsoidal variations and an apparent grazing eclipse. At this orbital period, the secondary stars in most CVs are substantially cooler, with spectral types near M3. ASN-13cl therefore joins the small group of CVs with anomalously warm secondary stars, which apparently form when the onset of mass transfer occurs after the secondary has undergone significant nuclear evolution.