HD 118203 is a star with an orbiting exoplanet 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.[7][8]
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Ursa Major |
| Right ascension | 13h 34m 02.5394s[1] |
| Declination | +53° 43′ 42.698″[1] |
| Apparent magnitude (V) | 8.06[2] |
| Characteristics | |
| Spectral type | G0V[3] |
| B−V color index | 0.699±0.012[4] |
| Astrometry | |
| Radial velocity (Rv) | −29.07±0.24[4] km/s |
| Proper motion (μ) | RA: −85.849(18) mas/yr[1] Dec.: −78.888(20) mas/yr[1] |
| Parallax (π) | 10.8643 ± 0.0180 mas[1] |
| Distance | 300.2 ± 0.5 ly (92.0 ± 0.2 pc) |
| Absolute magnitude (MV) | 3.32[2] |
| Details[5] | |
| Mass | 1.23±0.03 M☉ |
| Radius | 2.00±0.10 R☉ |
| Luminosity | 3.80±0.30 L☉ |
| Surface gravity (log g) | 3.93±0.02 cgs |
| Temperature | 5,741±35 K |
| Metallicity [Fe/H] | 0.16[2] dex |
| Rotational velocity (v sin i) | 7.0[2] km/s |
| Age | 5.4±0.5 Gyr |
| Other designations | |
| Database references | |
| SIMBAD | The star |
| planet b | |
| Exoplanet Archive | data |
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 300 light years from the Sun.[1] The star is drifting closer with a radial velocity of −29 km/s.[4] Based on its position and space velocity this is most likely (97% chance) an older thin disk star.[9] An exoplanet has been detected in a close orbit around the star.[10]
The spectrum of HD 118203 matches a G-type main-sequence star with a class of G0V.[3] It has a low level of chromospheric activity, which means a low level of radial velocity jitter for planet detection purposes.[10] The star has 1.23[5] 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.[5]
Exoplanet
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.[10] 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.[9]
| Companion (in order from star) | Mass | Semimajor axis (AU) | Orbital period (days) | Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b / Staburags | 2.173+0.077 −0.080 MJ | 0.07082+0.00095 −0.00110 | 6.134980+0.000038 −0.000037 | 0.316±0.021 | 88.75+0.86 −1.0° | 1.133+0.031 −0.030 RJ |