K2-28
K2-28 is a metal rich M4-type main sequence star. One confirmed transiting exoplanet is known to orbit this star. There is another star 5.2 arcseconds to the north–east of K2-28 however this star has a different proper motion and is therefore physically unrelated and probably a background star.[4]
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Aquarius[1] |
| Right ascension | 22h 22m 29.8611s[2] |
| Declination | −07° 57′ 19.853″[2] |
| Apparent magnitude (V) | 16.06[3] |
| Characteristics | |
| Spectral type | M4V[4][5] |
| Apparent magnitude (J) | 11.695±0.030[6] |
| Apparent magnitude (H) | 11.028±0.023[6] |
| Apparent magnitude (K) | 10.746±0.023[6] |
| Variable type | Planetary transit variable[4] |
| Astrometry | |
| Radial velocity (Rv) | 11.7[5] km/s |
| Proper motion (μ) | RA: −254.604(41)[2] mas/yr Dec.: −194.554(30)[2] mas/yr |
| Parallax (π) | 15.8734 ± 0.0343[2] mas |
| Distance | 205.5 ± 0.4 ly (63.0 ± 0.1 pc) |
| Details[4] | |
| Mass | 0.257±0.048 M☉ |
| Radius | 0.288±0.028 R☉ |
| Surface gravity (log g) | 4.93±0.04 cgs |
| Temperature | 3214±60 K |
| Metallicity [Fe/H] | 0.26±0.10 dex |
| Other designations | |
| Database references | |
| SIMBAD | data |
Planetary system
Discovery
K2-28b was first noticed as a candidate extrasolar planet by Vanderburg et al. in 2016, who, in a search of 59,174 stars from the Kepler space telescope's first year of K2 observations, found 234 planetary candidates.[8] Shortly thereafter the K2-ESPRINT Project confirmed that the candidate was a super-Earth sized planet in a close orbit around a red dwarf star.[4]
Characteristics
K2-28b is a sub-Neptune sized planet orbiting its star in only 2.26 days. Despite its short orbital period the equilibrium temperature of the planet is a relatively low 500 Kelvin due to the low luminosity of the parent star.[4] Because of the very small size of the parent star this planet is a particularly favorable target for transmission spectroscopy by the James Webb Space Telescope which should be able to determine if the atmosphere is cloudy or clear by observing roughly 5 transits.[9] Among a group of small and cool planets orbiting relatively bright M-dwarfs its predicted secondary eclipse depth of 230 parts-per-million is second only to Gliese 1214 b.[3]
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| K2-28b | 7.18+5.92 −3.08 (estimate) M⊕ |
0.0191+0.0037 −0.0029 |
2.2604455±0.0000010 | 0 | 87.1+0.90 −0.74° |
2.56+0.27 −0.26 R⊕ |
References
- Roman, Nancy G. (1987). "Identification of a Constellation From a Position". Publications of the Astronomical Society of the Pacific. 99 (617): 695–699. Bibcode:1987PASP...99..695R. doi:10.1086/132034. Vizier query form
- Brown, A. G. A.; et al. (Gaia collaboration). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics (in press). arXiv:2012.01533. doi:10.1051/0004-6361/202039657. S2CID 227254300. Gaia EDR3 record for this source at VizieR.
- Chen, Ge; et al. (2018). "An Improved Transit Measurement for a 2.4 R ⊕ Planet Orbiting A Bright Mid-M Dwarf K2–28". The Astronomical Journal. 155 (5). 223. arXiv:1801.10177. Bibcode:2018AJ....155..223C. doi:10.3847/1538-3881/aabd75.
- Hirano, Teruyuki; et al. (2016). "The K2-ESPRINT Project III: A Close-in Super-Earth around a Metal-rich Mid-M Dwarf". The Astrophysical Journal. 820 (1). 41. arXiv:1511.08508. Bibcode:2016ApJ...820...41H. doi:10.3847/0004-637X/820/1/41.
- Dressing, Courtney D.; et al. (2017). "Characterizing K2 Candidate Planetary Systems Orbiting Low-mass Stars. I. Classifying Low-mass Host Stars Observed during Campaigns 1–7". The Astrophysical Journal. 836 (2). 167. arXiv:1701.00586. Bibcode:2017ApJ...836..167D. doi:10.3847/1538-4357/836/2/167.
- Skrutskie, M. F.; et al. (2006). "The Two Micron All Sky Survey (2MASS)". The Astronomical Journal. 131 (2): 1163–1183. Bibcode:2006AJ....131.1163S. doi:10.1086/498708. Vizier catalog entry
- "K2-28". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-08-12.
- Vanderburg, Andrew; et al. (2016). "Planetary Candidates from the First Year of the K2 Mission". The Astrophysical Journal Supplement Series. 222 (1). 14. arXiv:1511.07820. Bibcode:2016ApJS..222...14V. doi:10.3847/0067-0049/222/1/14.
- Stefansson, Gudmundur; et al. (2018). "Diffuser-assisted Photometric Follow-up Observations of the Neptune-sized Planets K2-28b and K2-100b". The Astronomical Journal. 156 (6). 266. arXiv:1807.04420. Bibcode:2018AJ....156..266S. doi:10.3847/1538-3881/aae6ca.
