K2-18

K2-18, also known as EPIC 201912552, is a red dwarf star located 124 light-years (38 pc)[7] from Earth, in the constellation of Leo.

K2-18

Artist's impression of the K2-18 system, with K2-18 on left, K2-18b on right, and K2-18c between.
Credit: ESA/Hubble
Approximate two-dimensional location of the star (in red circle); Sigma Leonis is the nearest bright star, which is in a southerly direction, and the boundary of Virgo is similarly far.
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Leo
Right ascension 11h 30m 14.518s[1]
Declination +07° 35′ 18.26″[1]
Apparent magnitude (V) 13.50[2]
Characteristics
Evolutionary stage Red dwarf
Spectral type M2.8[3]
Astrometry
Proper motion (μ) RA: −80.377[1] mas/yr
Dec.: −133.142[1] mas/yr
Parallax (π)26.2686 ± 0.0546[1] mas
Distance124.2 ± 0.3 ly
(38.07 ± 0.08 pc)
Details
Mass0.495[4] M☉
Radius0.469[4] R☉
Luminosity0.0234[5] L☉
Temperature3,503[4] K
Metallicity [Fe/H]0.123±0.157[6] dex
Other designations
EPIC 201912552, UCAC4 488-054338, 2MASS J11301450+0735180
Database references
SIMBADdata

Planetary system

The star has an exoplanet, called K2-18b, a super-Earth located within the habitable zone of K2-18.[8][9] It is the first exoplanet in the habitable zone, albeit a gas giant,[10] to have water discovered in its atmosphere. The star also has a second planet K2-18c,[11] which is proven by system tidal simulation to be a small gas giant.[12]

The WASP-36 planetary system[12]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
c 5.62±0.84 M⊕ 0.0670 ± 0.0002 8.962±0.008 <0.2 — —
b 8.63±1.35 M⊕ 0.1591±0.0004 32.94488±0.00281 — — 2.711±0.065 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. Zacharias, N.; Finch, C. T.; Girard, T. M.; Henden, A.; Bartlett, J. L.; Monet, D. G.; Zacharias, M. I. (2012). "VizieR Online Data Catalog: UCAC4 Catalogue (Zacharias+, 2012)". VizieR On-line Data Catalog. Bibcode:2012yCat.1322....0Z.
  3. Montet, Benjamin T.; et al. (5 August 2015). "Stellar and Planetary Properties of K2 Campaign 1 Candidates and Validation of 17 Planets, Including a Planet Receiving Earth-like Insolation". The Astrophysical Journal. 809 (1): 25. arXiv:1503.07866. Bibcode:2015ApJ...809...25M. doi:10.1088/0004-637X/809/1/25. S2CID 33348734.
  4. Cloutier, R.; Astudillo-Defru, N.; Doyon, R.; Bonfils, X.; Almenara, J.-M.; Bouchy, F.; Delfosse, X.; Forveille, T.; Lovis, C.; Mayor, M.; Menou, K.; Murgas, F.; Pepe, F.; Santos, N. C.; Udry, S.; Wünsche, A. (2019). "Confirmation of the radial velocity super-Earth K2-18c with HARPS and CARMENES". Astronomy & Astrophysics. 621: A49. arXiv:1810.04731. Bibcode:2019A&A...621A..49C. doi:10.1051/0004-6361/201833995. S2CID 118828975.
  5. Martinez, Arturo O.; Crossfield, Ian J. M.; Schlieder, Joshua E.; Dressing, Courtney D.; Obermeier, Christian; Livingston, John; Ciceri, Simona; Peacock, Sarah; Beichman, Charles A.; Lépine, Sébastien; Aller, Kimberly M.; Chance, Quadry A.; Petigura, Erik A.; Howard, Andrew W.; Werner, Michael W. (2017). "Stellar and Planetary Parameters for K2's Late-type Dwarf Systems from C1 to C5". The Astrophysical Journal. 837 (1): 72. arXiv:1701.00588. Bibcode:2017ApJ...837...72M. doi:10.3847/1538-4357/aa56c7. S2CID 25502982.
  6. Benneke, Björn; Werner, Michael; Petigura, Erik; Knutson, Heather; Dressing, Courtney; Crossfield, Ian J. M.; Schlieder, Joshua E.; Livingston, John; Beichman, Charles; Christiansen, Jessie; Krick, Jessica; Gorjian, Varoujan; Howard, Andrew W.; Sinukoff, Evan; Ciardi, David R.; Akeson, Rachel L. (2017). "Spitzer Observations Confirm and Rescue the Habitable-zone Super-Earth K2-18b for Future Characterization". The Astrophysical Journal. 834 (2): 187. arXiv:1610.07249. Bibcode:2017ApJ...834..187B. doi:10.3847/1538-4357/834/2/187. S2CID 12988198.
  7. Cloutier, R.; et al. (7 January 2019). "Confirmation of the radial velocity super-Earth K2-18c with HARPS and CARMENES". Astronomy & Astrophysics. 621. A49. arXiv:1810.04731. Bibcode:2019A&A...621A..49C. doi:10.1051/0004-6361/201833995. S2CID 118828975.
  8. "HABITABLE EXOPLANETS CATALOG". UPR. 7 March 2016. Retrieved 12 September 2019.
  9. "EPIC 201912552 b reality check drewexmachina 11-22-2015". Drew ExMachina. 7 March 2016. Retrieved 12 September 2019.
  10. No, the Exoplanet K2-18b Is Not Habitable
  11. "EPIC 201912552". Open Exoplanet Catalogue. 7 March 2016. Retrieved 12 September 2019.
  12. Ferraz-Mello, S.; Gomes, G. O. (2020). "Tidal evolution of exoplanetary systems hosting potentially habitable exoplanets. The cases of LHS-1140 b-c and K2-18 b-c". Monthly Notices of the Royal Astronomical Society. 494 (4): 5082–5090. arXiv:2005.10318. Bibcode:2020MNRAS.494.5082G. doi:10.1093/mnras/staa1110. S2CID 218763252.


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