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KOI-81 is an
eclipsing binary A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in wh ...
star in the constellation of Cygnus. The primary star is a late B-type or early
A-type main-sequence star An A-type main-sequence star (A V) or A dwarf star is a main-sequence (hydrogen-burning) star of spectral type A and luminosity class V (five). These stars have spectra defined by strong hydrogen Balmer absorption lines. They measure between 1 ...
with a temperature of . It lies in the field of view of the
Kepler Mission The Kepler space telescope is a disused space telescope launched by NASA in 2009 to discover Earth-sized planets orbiting other stars. Named after astronomer Johannes Kepler, the spacecraft was launched into an Earth-trailing heliocentric orb ...
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 The Kepler space telescope is a disused space telescope launched by NASA in 2009 to discover Earth-sized planets orbiting other stars. Named after astronomer Johannes Kepler, the spacecraft was launched into an Earth-trailing heliocentric orb ...
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 A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun's, while its volume is comparable to the Earth's. A white dwarf's faint luminosity comes fro ...
of approximately 0.3
solar mass The solar mass () is a standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass ...
es, produced by a previous stage of
mass transfer Mass transfer is the net movement of mass from one location (usually meaning stream, phase, fraction or component) to another. Mass transfer occurs in many processes, such as absorption, evaporation, drying, precipitation, membrane filtration, ...
during the object's giant phase.


See also

*
KOI-74 KOI-74 () is an eclipsing binary star in the constellation of Cygnus (constellation), Cygnus. The primary star is an A-type main-sequence star with a temperature of . It lies in the field of view of the Kepler Mission and was determined to ...
, a similar system also discovered by the Kepler Mission. * Kepler Object of Interest, stars observed to have transits by the Kepler Mission


References

B-type main-sequence stars Cygnus (constellation) Eclipsing binaries White dwarfs 81 {{whitedwarf-star-stub