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Observation data
Epoch J2000      Equinox J2000
Constellation Cygnus[1][note 1]
Right ascension  19h 45m 25.4746s[2]
Declination +41° 5′ 33.8820″[2]
Apparent magnitude (V) 14.87[3]
Spectral type sdB[1]
Apparent magnitude (U) 13.80[3]
Apparent magnitude (B) 14.71[3]
Apparent magnitude (R) 15.43[3]
Apparent magnitude (I) 15.72[3]
Apparent magnitude (J) 15.36[3]
Apparent magnitude (H) 15.59[3]
Proper motion (μ) RA: 7.185±0.061[2] mas/yr
Dec.: −3.134±0.060[2] mas/yr
Parallax (π)0.7850 ± 0.0314[2] mas
Distance4,200 ± 200 ly
(1,270 ± 50 pc)
Mass0.496 ± 0.002[1] M
Radius0.203 ± 0.007[1] R
Luminosity (bolometric)22.9 ±  3.1 L
Temperature27,730 ± 260[1] K
Other designations
2MASS J19452546+4105339, KIC 5807616, KOI-55, UCAC2 46165657, UCAC3 263-170867, USNO-B1.0 1310-00349976.[3]
Database references

Kepler-70, formerly known as KOI-55, is a star in the constellation Cygnus with an apparent visual magnitude of 14.87.[3] This is too faint to be seen with the naked eye; viewing it requires a telescope with an aperture of 40 cm (20 in) or more.[4]

A subdwarf B star, Kepler-70 passed through the red giant stage some 18.4 million years ago. In its present-day state, it is fusing helium in its core. Once it runs out of helium it will contract to form a white dwarf. It has a relatively small radius of about 0.2 times the Sun's radius; white dwarfs are generally much smaller.[5] The star is host to a planetary system with two planets, Kepler-70b and Kepler-70c.[6] The innermost planet has the highest temperature of any known planet known so far.

Planetary system[edit]

On December 26, 2011, evidence for two extremely short-period planets was announced. They were detected by the reflection of starlight caused by the planets themselves, rather than through a variation in apparent stellar magnitude caused by them transiting the star.

The measurements also suggested a smaller body between the two confirmed planets; this remains unconfirmed.

Orbits of Kepler-70b and Kepler-70c have 7:10 orbital resonance and have the closest approach between planets of any known planetary system.

The Kepler-70 planetary system[6]
(in order from star)
Mass Semimajor axis
Orbital period
Eccentricity Inclination Radius
b 0.440 M 0.0060 0.2401 20–80, likely 65 [note 2]° 0.759 R
KOI-55.03 (unconfirmed) 0.222 M 0.0065  0.605 R
c 0.655 M 0.0076 0.34289 20–80, likely 65° 0.867 R


  1. ^ This is inferred from the RA and declination of the star.
  2. ^ inclinations are derived from brightness variations and lack of transits.


  1. ^ a b c d e "Notes for Planet KOI-55 b". Extrasolar Planet Database. Archived from the original on 19 January 2012. Retrieved 1 January 2012.
  2. ^ a b c d e Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  3. ^ a b c d e f g h i "KPD 1943+4058". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 1 January 2012.
  4. ^ Sherrod, P. Clay; Koed, Thomas L. (2003), A Complete Manual of Amateur Astronomy: Tools and Techniques for Astronomical Observations, Astronomy Series, Courier Dover Publications, p. 9, ISBN 0-486-42820-6
  5. ^ Cain, Fraser (4 February 2009). "White Dwarf Stars". Universe Today. Retrieved 8 January 2012.
  6. ^ a b Charpinet, S.; et al. (December 21, 2011), "A compact system of small planets around a former red-giant star", Nature, 480 (7378): 496–499, Bibcode:2011Natur.480..496C, doi:10.1038/nature10631, PMID 22193103

External links[edit]