HU Aquarii (abbreviated HU Aqr) is an eclipsing binary system approximately 623 away from the Sun, forming a cataclysmic variable of AM Herculis-type. The two stars orbit each other every 2.08 hours[ and the ultra-short binary system includes an eclipsing white dwarf and red dwarf.
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In 1993, Axel Schwope et al. discovered that the star, then called RXJ2107.9-0518, was both an eclipsing binary and a cataclysmic variable. The star had been flagged as a probable AM Herculis star from data collected during the ROSAT All Sky Survey.
Eclipse timing variations
The HU Aquarii binary system exhibits variations in the timing of the eclipses. Schwarz et al. (2009) note that the variations are too large to be caused by the Applegate mechanism, and are within the expected range of magnetic braking but 30 times too large to be caused by gravitational radiation alone. As an alternative explanation, they suggested that the variations might be caused by an object in orbit around the binary, causing it to move back and forth along the line-of-sight to the system.
See also
