K2-21
| Observation data EpochJ2000EquinoxJ2000 | |
|---|---|
| Constellation | Aquarius[1] |
| Right ascension | 22h41m12.88625s[2] |
| Declination | −14° 29′ 20.3492″[2] |
| Apparent magnitude(V) | 12.85[3] |
| Characteristics | |
| Evolutionary stage | Main sequence |
| Spectral type | M0.0±0.5V[3] |
| Apparent magnitude(B) | 14.14±0.06[3] |
| Apparent magnitude(V) | 12.85±0.02[3] |
| Apparent magnitude(G) | 12.268±0.003[2] |
| Apparent magnitude(J) | 10.251±0.021[4] |
| Apparent magnitude(H) | 9.633±0.022[4] |
| Apparent magnitude(K) | 9.417±0.020[4] |
| Astrometry | |
| Radial velocity(Rv) | 3.54±0.82[2]km/s |
| Proper motion(μ) | RA:20.672mas/yr[2] Dec.:-78.914mas/yr[2] |
| Parallax(π) | 11.9662 ± 0.0150mas[2] |
| Distance | 272.6 ± 0.3ly (83.6 ± 0.1pc) |
| Details[3] | |
| Mass | 0.64±0.11M☉ |
| Radius | 0.60±0.10R☉ |
| Luminosity (bolometric) | 0.086±0.064L☉ |
| Temperature | 4043±375K |
| Metallicity[Fe/H] | −0.11±0.13dex |
| Age | >1Gyr |
| Other designations | |
| Database references | |
| SIMBAD | data |
K2-21,also known asEPIC 206011691,is ared dwarfstar located 273light-years(84parsecs) away in the constellationAquarius.It hosts two knownexoplanets,discovered in 2015 by thetransit methodas part ofKepler's K2 mission.[3]Both planets have significantly lower densities than Earth, indicating that they are notrocky planetsand are better described asmini-Neptunes.The inner planet, K2-21b, is less dense than the outer planet, K2-21c.[5]
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | 1.59+0.52 −0.44M🜨 |
0.0731+0.0057 −0.0067[3] |
9.3238+0.0002 −0.0001 |
— | 88.54+0.49 −0.59° |
1.93±0.07R🜨 |
| c | 3.88+1.22 −1.07M🜨 |
0.1026+0.0079 −0.0094[3] |
15.5017±0.0002 | — | 89.02+0.33 −0.41° |
2.25±0.05R🜨 |
References[edit]
- ^"Finding the constellation which contains given sky coordinates".djm.cc.2 August 2008.
- ^abcdefVallenari, A.; et al. (Gaia collaboration) (2023)."GaiaData 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.S2CID244398875. Gaia DR3 record for this sourceatVizieR.
- ^abcdefghPetigura, 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.
- ^abcd"K2-21".SIMBAD.Centre de données astronomiques de Strasbourg.Retrieved24 May2023.
- ^abEl 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.
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