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]

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 to the subgiant 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. It is named Staburags. 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]