HD 204313 is a star with two and possibly three exoplanetary companions in the southern constellation of Capricornus. With an apparent magnitude of 7.99,[2] it is an eighth magnitude star that is too faint to be readily visible to the naked eye. The star is located at a distance of 157 light years from the Sun based on parallax measurements, but it is drifting closer with a radial velocity of −10 km/s.[1]
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Capricornus |
| Right ascension | 21h 28m 12.20609s[1] |
| Declination | −21° 43′ 34.5182″[1] |
| Apparent magnitude (V) | 7.99[2] |
| Characteristics | |
| Spectral type | G5V[3] |
| Apparent magnitude (B) | 8.687[2] |
| Apparent magnitude (J) | 6.812±0.024[2] |
| Apparent magnitude (H) | 6.539±0.040[2] |
| Apparent magnitude (K) | 6.459±0.018[2] |
| B−V color index | 0.697±0.022[2] |
| Astrometry | |
| Radial velocity (Rv) | −9.79±0.12[1] km/s |
| Proper motion (μ) | RA: 42.751 mas/yr[1] Dec.: −270.443 mas/yr[1] |
| Parallax (π) | 20.7705 ± 0.0343 mas[1] |
| Distance | 157.0 ± 0.3 ly (48.15 ± 0.08 pc) |
| Absolute magnitude (MV) | 4.61[2] |
| Details | |
| Mass | 1.06±0.03[4] M☉ |
| Radius | 1.08±0.03[4] R☉ |
| Luminosity | 1.18±0.03[4] L☉ |
| Surface gravity (log g) | 4.39±0.04[4] cgs |
| Temperature | 5,783±48[4] K |
| Metallicity [Fe/H] | 0.18[5] dex |
| Rotational velocity (v sin i) | 0.846[5] km/s |
| Age | 4.3±1.8[4] Gyr |
| Other designations | |
| Database references | |
| SIMBAD | data |
| Exoplanet Archive | data |
This is an ordinary G-type main-sequence star with a stellar classification of G5V,[3] which indicates it is generating energy through hydrogen fusion at its core. It is an estimated four billion years old, chromospherically extremely quiet,[7] and is spinning with a projected rotational velocity of just 0.8 km/s.[5] The star has a slightly larger mass and radius compared to the Sun. It is radiating 118% of the luminosity of the Sun from its photosphere at an effective temperature of 5,783 K.[4]
Planetary system
This star was in observation by the CORALIE radial velocity planet-search program since the year 2000. In August 2009, a superjovian planetary companion was announced.[8] Two years later, a hot Neptune HD 204313 c on a 35-day orbit was announced,[9] followed by a third Jupiter-like planet candidate HD 204313 d on a 2800-day orbit, which was announced in 2012.[10] Assuming that planet d exists, planets b & d are apparently orbiting close to a 7:5 mean motion resonance, which may be stabilizing their periods.[11]
A 2015 study independently confirmed the first two discoveries, but did not detect any significant signal at the claimed period of planet d.[12] Another study in 2022 agreed with these results, in addition to finding a new planet or brown dwarf, designated HD 204313 e to differentiate it from the dubious candidate. The inclination and true mass of planets b & e were measured via astrometry.[13]
| Companion (in order from star) | Mass | Semimajor axis (AU) | Orbital period (days) | Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| c | ≥17.6±1.7 M🜨 | 0.2099±0.0071 | 34.905±0.012 | 0.059+0.051 −0.041 | — | — |
| b | 4.615+1.290 −0.306 MJ | 3.185+0.130 −0.143 | 2041.1+1.7 −1.9 | 0.100±0.003 | 72.917+31.372 −21.476° | — |
| e | 15.317+4.890 −5.183 MJ | 7.457+0.399 −0.427 | 7325.6+399.9 −369.1 | 0.253+0.071 −0.065 | 176.092+0.963 −2.122° | — |