HD 204313

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]

HD 204313

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
CD–22°5691, GC 30045, HD 204313, HIP 106006, SAO 190362, PPM 272526, LTT 8525[6]
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]

The HD 204313 planetary system^[12][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°	—

See also

• HD 147018
• HD 171238
• List of extrasolar planets