Kepler-36

Kepler-36 is a star in the constellation of Cygnus with two known planets. It has an anomalously large radius, meaning that it is a subgiant.

Kepler-36
Observation data
Epoch J2000      Equinox J2000
Constellation Cygnus
Right ascension  19h 25m 00.0431s[1]
Declination +49° 13′ 54.631″[1]
Apparent magnitude (V) 11.9
Characteristics
Spectral type G1IV
Astrometry
Proper motion (μ) RA: 0.970±0.041[1] mas/yr
Dec.: −8.073±0.043[1] mas/yr
Parallax (π)1.8654 ± 0.0215[1] mas
Distance1,750 ± 20 ly
(536 ± 6 pc)
Details
Mass1.071[2] M☉
Radius1.626[2] R☉
Temperature5911[2] K
Metallicity [Fe/H]−0.2[2] dex
Other designations
KOI-277, KIC 11401755, 2MASS 19250004+4913545
Database references
SIMBADdata
KICdata

Planetary system

On June 21, 2012, the discovery of two planets orbiting the star was announced. The planets, a super-Earth and a "mini-Neptune", are unusual in that they have very close orbits; their semi-major axes differ by only 0.013 AU. The outer planet orbits only 11% further than the inner one. Coupled with masses significantly higher than Earth, their gravitational influence to each other is significant, meaning that their interaction causes extreme transit timing variations for both. Kepler-36b and c have estimated densities of 6.8 and 0.86 g/cm3, respectively.[2] The two planets are close to a 7:6 orbital resonance.[2] The large difference in densities, despite the close proximity of the planets' orbits, is likely due to the large difference in mass.[3] The innermost and less massive planet likely lost most, or all, of the hydrogen/helium envelope acquired during formation.

The Kepler-36 planetary system[2]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b 4.45 M⊕ 0.1153 13.83989 <0.04 90.0° 1.486 R⊕
c 8.08 M⊕ 0.1283 16.23855 <0.04 90.0° 3.679 R⊕

References
  1. 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.
  2. Carter, J. A.; et al. (2012). "Kepler-36: A Pair of Planets with Neighboring Orbits and Dissimilar Densities". Science. 337 (6094): 556–559. arXiv:1206.4718. Bibcode:2012Sci...337..556C. doi:10.1126/science.1223269. PMID 22722249.
  3. Bodenheimer, P.; Stevenson, D.; Lissauer, J.; D'Angelo, G. (2018). "New Formation Models for the Kepler-36 System". The Astrophysical Journal. 868 (2): id. 138 (17 pp.). arXiv:1810.07160. Bibcode:2018ApJ...868..138B. doi:10.3847/1538-4357/aae928.
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