KOI-256 is a

double star In observational astronomy, a double star or visual double is a pair of stars that appear close to each other as viewed from Earth, especially with the aid of optical telescopes. This occurs because the pair either forms a binary star (i.e. a bi ...

located in the constellation Cygnus approximately from Earth. While observations by the ''Kepler'' spacecraft suggested the system contained a gas giant

exoplanet An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...

orbiting a

red dwarf ''Red Dwarf'' is a British science fiction comedy franchise created by Rob Grant and Doug Naylor, which primarily consists of a television sitcom that aired on BBC Two between 1988 and 1999, and on Dave since 2009, gaining a cult following. T ...

, later studies determined that KOI-256 was a binary system composed of the red dwarf orbiting a white dwarf.

Name

The acronym "KOI" comes from '' Kepler object of interest'' and means that the object has been cataloged by the '' Kepler'' spacecraft during its search for extrasolar planets using the transit method. The "256" is the number of the object.

Characteristics

Initial observations by the ''Kepler'' spacecraft suggested a central

with a mass of , a radius of , and a temperature of . Its candidate

was estimated to have a mass of , a radius of , an orbital period of 1.38 days, a temperature of , and a

semi-major axis In geometry, the major axis of an ellipse is its longest diameter: a line segment that runs through the center and both foci, with ends at the two most widely separated points of the perimeter. The semi-major axis (major semiaxis) is the long ...

of 0.021 astronomical units. Further studies by Muirhead ''et al.'' (2012) refined the candidate exoplanet parameters to a radius of , a temperature of , and a semi-major axis of 0.016 AU. Muirhead ''et al.'' (2013) performed additional observations with the Hale Telescope at

Palomar Observatory Palomar Observatory is an astronomical research observatory in San Diego County, California, United States, in the Palomar Mountain Range. It is owned and operated by the California Institute of Technology (Caltech). Research time at the observat ...

. Using the

radial velocity method Doppler spectroscopy (also known as the radial-velocity method, or colloquially, the wobble method) is an indirect method for finding extrasolar planets and brown dwarfs from radial-velocity measurements via observation of Doppler shifts in ...

for exoplanet detection, Muirhead's team found that the red dwarf was wobbling too much to be caused by a planetary mass object, and was more likely being influenced by a white dwarf. Using ultraviolet data from the

GALEX Galaxy Evolution Explorer (GALEX or Explorer 83 or SMEX-7) was a NASA orbiting space telescope designed to observe the universe in ultraviolet wavelengths to measure the history of star formation in the universe. In addition to paving the ...

spacecraft, it was seen that the red dwarf was significantly active, further suggesting perturbations by a white dwarf. The team re-analyzed ''Kepler'' data, and found that when the white dwarf passed in front of the red dwarf, the red dwarf's light noticeably warped and brightened, an effect called gravitational lensing. While only being slightly larger than the Earth, the white dwarf has such large mass that the physically larger red dwarf orbits around its smaller companion. With the new observations, the red dwarf was shown to have a mass of , a radius of , and a temperature of . The white dwarf has a mass of , a radius of , and a temperature of .

References

{{Stars of Cygnus, state=collapsed Astronomical objects discovered in 2009 Cygnus (constellation) Eclipsing binaries

256 Year 256 ( CCLVI) was a leap year starting on Tuesday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Claudius and Glabrio (or, less frequently, year 1009 ''Ab urbe condi ...

J19004443 M-type main-sequence stars