| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Aquarius |
| Right ascension | 22 41 12.88625 |
| 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 |
| Distance | 272.6 ± 0.3 ly (83.6 ± 0.1 pc) |
| Details | |
| Mass | 0.64±0.11 M☉ |
| Radius | 0.60±0.10 R☉ |
| Luminosity (bolometric) | 0.086±0.064 L☉ |
| Temperature | 4043±375 K |
| Metallicity | −0.11±0.13 dex |
| Age | >1 Gyr |
| Other designations | |
| K2-21, EPIC 206011691, TIC 240766850, 2MASS J22411288-1429202 | |
| Database references | |
| SIMBAD | data |
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.
| 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
- "Finding the constellation which contains given sky coordinates". djm.cc. 2 August 2008.
- ^ 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.
- ^ 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.
- ^ "K2-21". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 24 May 2023.
- ^ 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.
| The K2-21 system | |
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