HD 202206

HD 202206 is a binary star system in the southern constellation of Capricornus. With an apparent visual magnitude of +8.1,^[3] it is too faint to be visible to the naked eye. It is located at a distance of 150 light years from the Sun based on parallax, and is drifting further away with a radial velocity of +14.7 km/s.^[5]

HD 202206

Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Capricornus[1]
Right ascension	21h 14m 57.76850s[2]
Declination	−20° 47′ 21.1624″[2]
Apparent magnitude (V)	+8.07±0.01[3]
Characteristics
Spectral type	G6V[4] + M8V[3]
B−V color index	0.714±0.012[1]
Astrometry
Radial velocity (Rv)	+14.68±0.23[5] km/s
Proper motion (μ)	RA: −39.079[2] mas/yr Dec.: −119.999[2] mas/yr
Parallax (π)	21.7264±0.0651 mas[2]
Distance	150.1 ± 0.4 ly (46.0 ± 0.1 pc)
Absolute magnitude (MV)	+4.80[1]
Orbit[3]
Period (P)	256.33 days
Semi-major axis (a)	1.40±0.10 mas
Eccentricity (e)	0.432±0.001
Inclination (i)	10.9±0.8°
Longitude of the node (Ω)	121±4°
Periastron epoch (T)	2,452,176.14±0.12 JD
Argument of periastron (ω) (secondary)	161.9±0.2°
Semi-amplitude (K1) (primary)	0.567±0.001 km/s
Details
A
Mass	1.07±0.08[3] M☉
Radius	1.05+0.02 −0.03[2] R☉
Luminosity	1.084+0.004 −0.005[2] L☉
Surface gravity (log g)	4.5±0.1[3] cgs
Temperature	5,735+76 −74[2] K
Metallicity [Fe/H]	0.29±0.01[1] dex
Rotational velocity (v sin i)	2.3±0.5[3] km/s
Age	2.9±1.0[3] Gyr
B
Mass	0.089+0.007 −0.006[3] M☉
Other designations
BD−21°5972, HD 202206, HIP 104903, SAO 190163[6]
Database references
SIMBAD	data

The primary component is a G-type main-sequence star with a stellar classification of G6V,^[4] indicating it is generating energy through core hydrogen fusion. It is an estimated three^[3] billion years old and is spinning with a projected rotational velocity of 2.3 km/s.^[3] It is a metal-rich star – what astronomers term the abundance of elements of higher atomic number than helium – which may explain the star's unusually high luminosity for its class.^[7] The star has a slightly greater mass and radius compared to the Sun.^[3]

Companions

In 2000, analysis of radial velocity measurements of the star revealed the existence of a brown dwarf companion^[8] with at least 17 times the mass of Jupiter around the star in an eccentric orbit with a period of around 256 days.^[7] Even after the brown dwarf was accounted for, the star still showed a drift in the radial velocity measurements, suggesting another companion in a longer-period orbit. In 2004 after further observations, the parameters of a proposed companion was announced.^[9]

Further observation of this system revised this picture in 2017, showing that the system instead consisted of a pair of co-orbiting stars being viewed nearly face-on, with the pair being orbited in turn by a Super-Jupiter designated HD 202206 c. The secondary stellar companion, now designated component B rather than 'b', is a red dwarf star with 8.9% of the mass of the Sun.^[3]

The HD 202206 planetary system^[3]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
c	17.9+2.9 −1.8 MJ	2.41	1,260±11	0.22±0.03	7.7±1.1°	—