K2-21

K2-21
Observation data
Epoch J2000      Equinox ICRS
Constellation Aquarius
Right ascension 22h 41m 12.88625s
Declination −14° 29′ 20.3492″
Apparent magnitude (V) 12.85
Characteristics
Evolutionary stage Main sequence
Spectral type M0.0±0.5V
Apparent magnitude (B) 14.14±0.06
Apparent magnitude (V) 12.85±0.02
Apparent magnitude (G) 12.268±0.003
Apparent magnitude (J) 10.251±0.021
Apparent magnitude (H) 9.633±0.022
Apparent magnitude (K) 9.417±0.020
Astrometry
Radial velocity (Rv)3.54±0.82 km/s
Proper motion (μ) RA: 20.672 mas/yr
Dec.: -78.914 mas/yr
Parallax (π)11.9662±0.0150 mas
Distance272.6 ± 0.3 ly
(83.6 ± 0.1 pc)
Details
Mass0.64±0.11 M☉
Radius0.60±0.10 R☉
Luminosity (bolometric)0.086±0.064 L☉
Temperature4043±375 K
Metallicity [Fe/H]−0.11±0.13 dex
Age>1 Gyr
Other designations
K2-21, EPIC 206011691, TIC 240766850, 2MASS J22411288-1429202
Database references
SIMBADdata
Exoplanet Archivedata

K2-21, also known as EPIC 206011691, is a red dwarf star located 273 light-years (84 parsecs) away in the constellation Aquarius. It hosts two known exoplanets, discovered in 2015 by the transit method as part of Kepler's K2 mission. Both planets have significantly lower densities than Earth, indicating that they are not rocky planets and are better described as mini-Neptunes. The inner planet, K2-21b, is less dense than the outer planet, K2-21c.

The K2-21 planetary system
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination
(°)		 Radius
b 1.59+0.52
−0.44 M🜨		 0.0731+0.0057
−0.0067		 9.3238+0.0002
−0.0001		 — 88.54+0.49
−0.59		 1.93±0.07 R🜨
c 3.88+1.22
−1.07 M🜨		 0.1026+0.0079
−0.0094		 15.5017±0.0002 — 89.02+0.33
−0.41		 2.25±0.05 R🜨

References

  1. ↑ Roman, Nancy G. (1987). "Identification of a constellation from a position". Publications of the Astronomical Society of the Pacific. 99 (617): 695. Bibcode:1987PASP...99..695R. doi:10.1086/132034. Constellation record for this object at VizieR.
  2. 1 2 3 4 5 6 7 8 Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  3. 1 2 3 4 5 6 7 8 Petigura, Erik A.; et al. (2015). "Two Transiting Earth-Size Planets Near Resonance Orbiting a Nearby Cool Star". The Astrophysical Journal. 811 (2) 102. arXiv:1507.08256. Bibcode:2015ApJ...811..102P. doi:10.1088/0004-637X/811/2/102.
  4. 1 2 3 4 "K2-21". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 24 May 2023.
  5. 1 2 El Moutamid, Maryame; et al. (April 2023). "Mass derivation of planets K2-21b and K2-21c from transit timing variations". Monthly Notices of the Royal Astronomical Society. 520 (3): 4226–4234. arXiv:2305.11359. Bibcode:2023MNRAS.520.4226E. doi:10.1093/mnras/stad238.