HS Hydrae

HS Hydrae is a detached eclipsing binary star system located in the constellation Hydra. It is composed of two white dwarf stars orbiting each other with a period of approximately 2.3 hours. One of the white dwarfs is significantly more massive than the other, and the system is a prototype for a class of eclipsing binaries known as pre-cataclysmic variables (pre-CVs).

The system is notable because the less massive white dwarf fills its Roche lobe, causing mass transfer onto the more massive white dwarf. This mass transfer is not stable, and over time, the system is expected to evolve into a cataclysmic variable star, where the mass transfer rate increases dramatically and the system undergoes outbursts.

HS Hydrae has been extensively studied to understand the evolution of close binary stars and the processes leading to cataclysmic variable formation. Observations have been made across a wide range of wavelengths, from X-rays to infrared, to characterize the physical properties of the two white dwarfs and the mass transfer process. Precise timing of the eclipses allows for the accurate determination of the orbital parameters of the system.