KOI-81

KOI-81 is an eclipsing binary star in the constellation of Cygnus. The primary star is a late B-type [main-sequence star|B-type] or early A-type main-sequence star with a temperature of. It lies in the field of view of the Kepler Mission and was determined to have an object in orbit around it which is smaller and hotter than the main star.

KOI-81b

KOI-81b is a hot compact object orbiting KOI-81. It was discovered in 2010 by the Kepler Mission and came to attention because of its small size and high temperature of. The orbit of KOI-81b around the main star takes 23.8776 days to complete. Analysis of relativistic effects in the Kepler light curve suggests that it is a low-mass white dwarf of approximately 0.3 solar masses, or the immediate progenitor of such a white dwarf, a hot subdwarf. This small hot star was produced by mass transfer when the primary stripped the outer layers when the secondary expanded after leaving the main sequence.