A deeply eclipsing detached double helium white dwarf binary

TL;DR

This paper reports the discovery and detailed characterization of CSS 41177, a rare eclipsing double helium white dwarf binary, providing precise mass and radius measurements and insights into its future evolution.

Contribution

The study presents the first detailed analysis of CSS 41177, the second known eclipsing double white dwarf binary, including spectroscopic and photometric measurements for mass and radius determination.

Findings

Both white dwarfs are helium core with masses around 0.28 Msun.

The binary will merge in approximately 1.1 billion years.

The system's properties enable precise, model-independent measurements.

Abstract

Using Liverpool Telescope+RISE photometry we identify the 2.78 hour period binary star CSS 41177 as a detached eclipsing double white dwarf binary with a 21,100K primary star and a 10,500K secondary star. This makes CSS 41177 only the second known eclipsing double white dwarf binary after NLTT 11748. The 2 minute long primary eclipse is 40% deep and the secondary eclipse 10% deep. From Gemini+GMOS spectroscopy we measure the radial velocities of both components of the binary from the H{\alpha} absorption line cores. These measurements, combined with the light curve information, yield white dwarf masses of M1 = 0.283\pm0.064Msun and M2 = 0.274\pm0.034Msun, making them both helium core white dwarfs. As an eclipsing, double-lined spectroscopic binary CSS 41177 is ideally suited to measuring precise, model-independent masses and radii. The two white dwarfs will merge in roughly 1.1 Gyr to form a single sdB star.