HD 118203

HD 118203 is a star located in the northern circumpolar constellation of Ursa Major. It has the proper name Liesma, which means flame, and it is the name of a character from the Latvian poem Staburags un Liesma (Staburags and Liesma). The name was selected in the NameExoWorlds campaign by Latvia, during the 100th anniversary of the IAU.[6][7]

HD 118203
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Ursa Major
Right ascension 13h 34m 02.5394s[1]
Declination +53° 43′ 42.6984″[1]
Apparent magnitude (V) 8.06[2]
Characteristics
Spectral type K0IV
B−V color index 0.699±0.012[3]
Astrometry
Radial velocity (Rv)−29.07±0.24[3] km/s
Proper motion (μ) RA: −85.877±0.052[1] mas/yr
Dec.: −78.913±0.038[1] mas/yr
Parallax (π)10.8102 ± 0.0275[1] mas
Distance301.7 ± 0.8 ly
(92.5 ± 0.2 pc)
Absolute magnitude (MV)3.32[2]
Details[4]
Mass1.23±0.03 M☉
Radius2.00±0.10 R☉
Luminosity3.80±0.30 L☉
Surface gravity (log g)3.93±0.02 cgs
Temperature5,741±35 K
Metallicity [Fe/H]0.16[2] dex
Rotational velocity (v sin i)7.0[2] km/s
Age5.4±0.5 Gyr
Other designations
BD+54°1609, HD 118203, HIP 66192, SAO 28802,[5] TOI 1271
Database references
SIMBADThe star
planet b
Exoplanet Archivedata

The apparent visual magnitude of HD 118203 is 8.06,[2] which means it is invisible to the naked eye but it can be seen using binoculars or a telescope. Based on parallax measurements, it is located at a distance of 302 light years from the Sun.[1] The star is drifting closer with a radial velocity of −29 km/s.[3] Based on its position and space velocity this is most likely (97% chance) an older thin disk star.[8] An exoplanet has been detected in a close orbit around the star.[9]

The spectrum of this star matches a K-type dwarf with a class of K0. Its absolute magnitude of 3.32[2] is too high for a K-type main-sequence star, indicating that it has begun to evolve on the subdwarf stage. This is confirmed by the surface gravity, which is too low for a typical dwarf star of this class. It has a low level of chromospheric activity, which means a low level of radial velocity jitter for planet detection purposes.[9] The star has 1.23[4] times the mass of the Sun and double the Sun's radius. It is around 5.4 billion years old and is spinning with a projected rotational velocity of 7.0 km/s.[2] HD 118203 is radiating 3.8 times the luminosity of the Sun from its photosphere at an effective temperature of 5,741 K.[4]

In 2006, a hot Jupiter candidate was reported in an eccentric orbit around this star. It was discovered using the radial velocity method based on observation of high-metallicity stars begun in 2004.[9] In 2020, it was found that this is a transiting planet, which allowed the mass and radius of the body to be determined. This exoplanet has more than double the mass of Jupiter and a 13% greater radius. The fact that the parent star is among the brighter known planet hosts (as of 2020) makes it an interesting object for further study.[8]

The HD 118203 planetary system[8]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b 2.173+0.077
−0.080 MJ		 0.07082+0.00095
−0.0011		 6.134980+0.000038
−0.000037		 0.316±0.021 88.75+0.86
−1.0°		 1.133+0.031
−0.030 RJ

See also

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. Luck, R. Earle (January 2017). "Abundances in the Local Region II: F, G, and K Dwarfs and Subgiants". The Astronomical Journal. 153 (1): 19. arXiv:1611.02897. Bibcode:2017AJ....153...21L. doi:10.3847/1538-3881/153/1/21. S2CID 119511744. 21.
  3. Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. S2CID 119257644.
  4. Bonfanti, A.; et al. (2015). "Age consistency between exoplanet hosts and field stars". Astronomy & Astrophysics. 585: A5. arXiv:1511.01744. Bibcode:2016A&A...585A...5B. doi:10.1051/0004-6361/201527297. S2CID 53971692.
  5. "HD 118203". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-10-13.
  6. "Approved names". NameExoworlds. Retrieved 2020-01-02.
  7. "International Astronomical Union | IAU". www.iau.org. Retrieved 2020-01-02.
  8. Pepper, Joshua; et al. (2020). "TESS Reveals HD 118203 b to be a Transiting Planet". The Astronomical Journal. 159 (6): 243. arXiv:1911.05150. Bibcode:2020AJ....159..243P. doi:10.3847/1538-3881/ab84f2. S2CID 207930540.
  9. da Silva, R.; et al. (2006). "Elodie metallicity-biased search for transiting Hot Jupiters I. Two Hot Jupiters orbiting the slightly evolved stars HD118203 and HD149143". Astronomy and Astrophysics. 446 (2): 717–722. arXiv:astro-ph/0510048. Bibcode:2006A&A...446..717D. doi:10.1051/0004-6361:20054116.

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