CSS J134052.0+151341 : A Cataclysmic Binary Star with a Stripped, Evolved Secondary

TL;DR

This paper presents spectroscopic and photometric analysis of CSS J134052.0+151341, revealing it as a rare cataclysmic binary with a stripped, evolved secondary star, challenging typical binary star models.

Contribution

It provides the first detailed characterization of a cataclysmic binary with an evolved, stripped secondary star, highlighting a rare evolutionary pathway.

Findings

Secondary star classified as K4, but with a very short orbital period.

Spectral evidence of processed surface material with enhanced sodium lines.

The secondary is likely the core remnant of a more massive star.

Abstract

I report spectroscopy and time-series photometry of the cataclysmic binary CSS J134052.0+151341. The optical light is dominated by the secondary star, which I classify as K4 (+-2 subclasses), yet the orbital period derived from the absorption radial velocities is only 2.45 hr, implying a Roche radius much too small to contain a main-sequence K star. The spectrum shows enhanced sodium absorption in several lines, suggesting that the surface material has been processed at high temperatures. CSS J134052.0+151341 appears to be a rare example of a cataclysmic binary in which the secondary star is the stripped core of a formerly much more massive star, that began mass transfer after much of the core's nuclear evolution had taken place.