| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Ursa Major[1] |
| Right ascension | 13h 34m 02.5394s[2] |
| Declination | +53° 43′ 42.698″[2] |
| Apparent magnitude (V) | 8.06[3] |
| Characteristics | |
| Spectral type | G0V[4] |
| B−Vcolor index | 0.699±0.012[1] |
| Astrometry | |
| Radial velocity (Rv) | −29.37±0.13[2] km/s |
| Proper motion (μ) | RA: −85.849(18)mas/yr[2] Dec.: −78.888(20)mas/yr[2] |
| Parallax (π) | 10.8643±0.0180 mas[2] |
| Distance | 300.2 ± 0.5 ly (92.0 ± 0.2 pc) |
| Absolute magnitude (MV) | 3.32[3] |
| Details[5] | |
| Mass | 1.353±0.006 M☉ |
| Radius | 1.993±0.065 R☉ |
| Luminosity | 4.42±0.02 L☉ |
| Surface gravity (log g) | 4.05±0.04 cgs |
| Temperature | 5,872±20 K |
| Metallicity [Fe/H] | 0.27±0.02 dex |
| Rotational velocity (v sin i) | 7.0[3] km/s |
| Age | 5.4±0.5[6] Gyr |
| Other designations | |
| Liesma,BD+54°1609,HD 118203,HIP 66192,SAO 28802,TOI-1271,TIC 286923464,TYC 3850-458-1[7] | |
| Database references | |
| SIMBAD | The star |
| planet b | |
| Exoplanet Archive | data |
HD 118203 is astar with an orbitingexoplanet located in the northerncircumpolar constellation ofUrsa Major. It has the proper nameLiesma, which meansflame, and it is the name of a character from the Latvian poemStaburags un Liesma (Staburags and Liesma). The name was selected in theNameExoWorlds campaign byLatvia, during the 100th anniversary of theIAU.[8][9]
Theapparent visual magnitude of HD 118203 is 8.06,[3] which means it is invisible to the naked eye but it can be seen usingbinoculars or atelescope. Based onparallax measurements, it is located at a distance of 300 light years from theSun.[2] The star is drifting closer with aradial velocity of −29 km/s.[1] Based on its position andspace velocity this is most likely (97% chance) an olderthin disk star.[10] Anexoplanet has been detected in a close orbit around the star.[11]
Thespectrum of HD 118203 matches aG-type main-sequence star with aclass of G0V.[4] It has a low level ofchromospheric activity, which means a low level of radial velocity jitter for planet detection purposes.[11] The star has 1.23[6] times themass of the Sun and double theSun's radius. It is around 5.4 billion years old and is spinning with aprojected rotational velocity of 7.0 km/s.[3] HD 118203 is radiating 3.8 times theluminosity of the Sun from itsphotosphere at aneffective temperature of 5,741 K.[6]
In 2006, ahot Jupiter,HD 118203 b, was reported in an eccentric orbit around this star. It was discovered using theradial velocity method based on observation of high-metallicity stars begun in 2004.[11] In 2020, it was found that this is atransiting planet, which allowed the mass and radius of the body to be determined. This exoplanet has more than double the mass of Jupiter and is 13% greater in 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.[10] This planet received the proper name Staburags in the 2019NameExoWorlds campaign.[8]
In 2024, the star HD 118203 was found to display variability with a period matching that of planet b's orbit, suggesting magnetic interaction between the star and planet.[5]
Also in 2024, a second massive planet was discovered using radial velocity observations as well asHipparcos andGaiaastrometry. HD 118203 c is about 11 times the mass of Jupiter and takes 14 years to complete an orbit around the star. Like planet b, the orbit of planet c is close to edge-on, suggesting an aligned planetary system. The presence of any additional transiting planets at least twice the size of Earth and with periods less than 100 days was ruled out by the observations.[12]
| Companion (in order from star) | Mass | Semimajor axis (AU) | Orbital period (days) | Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b / Staburags | 2.182±0.033 MJ | 0.0701±0.0004 | 6.1349890(13) | 0.301±0.006 | 88.9+0.8 −1.0° | 1.12±0.09 RJ |
| c | 11.1+1.3 −1.0 MJ | 6.20±0.20 | 5070+240 −230 | 0.257±0.034 | 95+15 −19° | — |
