RR Caeli

Properties

RR Caeli was first noted to be a high-proper motion star in 1955 by Jacob Luyten, and given the designation LFT 349.

This star system consists of a red dwarf of spectral type M6 and a white dwarf that orbit each other every seven hours; the former is 18% as massive as the Sun, while the latter has 44% of the Sun's mass. The red dwarf is tidally locked with the white dwarf, meaning it displays the same side to the heavier star. The system is also a post-common-envelope binary, and the red dwarf star is transferring material onto the white dwarf. In approximately 9–20 billion years, RR Caeli will likely become a cataclysmic variable star due to the period's gradual shortening, leading to increasing rates of transfer of hydrogen to the surface of the white dwarf. The white dwarf is likely to have a plain helium core, as its density is too low for the carbon-oxygen core.

Discovered to be an eclipsing binary in 1979, it has a baseline magnitude of 14.36, dimming markedly every 7.2 hours for an interval of around 10 minutes, due to the total eclipse of the hotter star by the cooler one. Its variability in brightness led to its being given the variable star designation RR Caeli in 1984. There are very shallow secondary eclipses where the white dwarf transits across the red dwarf.