KOI-256

KOI-256

White dwarf companion gravitationally bending the starlight of KOI-256
Observation data Epoch J2000      Equinox J2000
Constellation	Cygnus
Right ascension	19h 00m 44.43s
Declination	+49° 33′ 55.33″
Characteristics
Evolutionary stage	Red dwarf (M3)
Spectral type	V
Apparent magnitude (Kepler)	15.37
Apparent magnitude (J)	7001127010000000000♠12.701±0.024
Apparent magnitude (H)	7001120010000000000♠12.001±0.019
Apparent magnitude (Ks)	7001117830000000000♠11.783±0.023
Apparent magnitude (r)	15.754
Apparent magnitude (i)	14.636
Apparent magnitude (z)	14.059
R−I color index	1.118
J−H color index	6999700000000000000♠0.700±0.031
J−K color index	6999918000000000000♠0.918±0.033
Evolutionary stage	White dwarf (D)
Apparent magnitude (Kepler)	19.45
Astrometry
Distance	1828 ly (560 pc)
Details
Red dwarf
Mass	6999510000000000000♠0.51±0.16 M☉
Radius	6999540000000000000♠0.540±0.014 R☉
Temperature	7003345000000000000♠3450±50 K
Metallicity	6999310000000000000♠+0.31±0.10
White dwarf
Mass	6999592000000000000♠0.592±0.089 M☉
Radius	6998134500000000000♠0.01345±0.00091 R☉
Temperature	7003710000000000000♠7100±800 K
Other designations
KOI-256, KIC 11548140, 2MASS J19004443+4933553
Database references
SIMBAD	data
Exoplanet Archive	data
KIC	data

KOI-256 is a double star located in the constellation Cygnus approximately 560 parsecs (1,828 ly) from Earth.^[1] While observations by the Kepler spacecraft suggested the system contained a gas giant exoplanet orbiting a red dwarf, later studies determined that KOI-256 was a binary system composed of the red dwarf orbiting a white dwarf.^[2][3]

Name

KOI-256

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 red dwarf with a mass of 0.65 M_☉, a radius of 1.1 R_☉, and a temperature of 3,639 K (3,366 °C; 6,091 °F). Its candidate exoplanet was estimated to have a mass of 14.8 M_⊕, a radius of 25.34 R_⊕, an orbital period of 1.38 days, a temperature of 1,160 K (890 °C; 1,630 °F), and a semi-major axis of 0.021 astronomical units.^[4][5] Further studies by Muirhead et al. (2012) refined the candidate exoplanet parameters to a radius of 7000559999999999999♠5.60±0.76  R_⊕, a temperature of 726 K (453 °C; 847 °F), and a semi-major axis of 0.016 AU.^[6]

Muirhead et al. (2013) performed additional observations with the Hale Telescope at Palomar Observatory. Using the radial velocity method 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 spacecraft, it was seen that the red dwarf was significantly active, further suggesting perturbations by a white dwarf. The team re-analyzed Kepler's 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.^[2]

With the new observations, the red dwarf was shown to have a mass of 6999510000000000000♠0.51±0.15  M_☉, a radius of 6999540000000000000♠0.540±0.014  R_☉, and a temperature of 3,450 ± 50 K (3,180 ± 50 °C; 5,750 ± 90 °F). The white dwarf has a mass of 6999592000000000000♠0.592±0.084  M_☉, a radius of 6998134500000000000♠0.01345±0.00091  R_☉, and a temperature of 7,100 ± 800 K (6,800 ± 800 °C; 12,300 ± 1,400 °F).^[7]

References