HD 171238

HD 171238 is a star with an orbiting exoplanet in the southern constellation of Sagittarius. It is located at a distance of 145 light years from the Sun based on parallax measurements, and is drifting further away with a radial velocity of 21 km/s.^[6] The star has an absolute magnitude of 5.15,^[5] but at the distance of this system it is too faint to be viewed with the naked eye, having an apparent visual magnitude of 8.61.^[2]

HD 171238

Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Sagittarius
Right ascension	18h 34m 43.676s[1]
Declination	−28° 04′ 20.33″[1]
Apparent magnitude (V)	8.606[2]
Characteristics
Evolutionary stage	Main sequence
Spectral type	G8 V[3]
Apparent magnitude (B)	9.40
Apparent magnitude (J)	7.244[4]
Apparent magnitude (H)	6.868[4]
Apparent magnitude (K)	6.831[4]
B−V color index	0.74[5]
Astrometry
Radial velocity (Rv)	21.11±0.17[6] km/s
Proper motion (μ)	RA: −29.539 mas/yr[1] Dec.: −109.580 mas/yr[1]
Parallax (π)	22.4809±0.0324 mas[1]
Distance	145.1 ± 0.2 ly (44.48 ± 0.06 pc)
Absolute magnitude (MV)	5.15[5]
Details
Mass	0.99±0.01[7] M☉
Radius	0.95±0.01[7] R☉
Luminosity	0.774±0.003[7] L☉
Surface gravity (log g)	4.47±0.01[7] cgs
Temperature	5,570±21[7] K
Metallicity [Fe/H]	0.17±0.007[5] dex
Rotational velocity (v sin i)	1.48[5] km/s
Age	4.0±1.2[7] Gyr
Other designations
CD–28°14719, HD 171238, HIP 91085, SAO 186998, PPM 268605[8]
Database references
SIMBAD	data
Exoplanet Archive	data

The spectrum of HD 171238 presents as an ordinary G-type main-sequence star with a stellar classification of G8 V.^[3] At an estimated age of around four billion years,^[7] it is spinning with a projected rotational velocity of 1.5 km/s.^[5] The metallicity of the star – the abundance of elements more massive than helium – is 48% higher than solar, based on the abundance of iron.^[5] There are indications of a significant level of magnetic activity in the chromosphere.^[5] The star has 99% of the mass of the Sun and 95% of the Sun's girth. It is radiating just 77% of the luminosity of the Sun from its photosphere at an effective temperature of 5,570 K.^[7]

Planetary system

In August 2009, it was announced that this star has a super-jovian exoplanet.^[5] Using astrometry from Gaia, astronomers were able to deduce the true mass of HD 171238 b as 8.8 M_J; higher than the minimum mass estimated from Doppler spectroscopy.^[9]

The HD 171238 planetary system^[9]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (years)	Eccentricity	Inclination	Radius
b	8.8+3.6 −1.3 MJ	2.518+0.032 −0.033	4.148+0.045 −0.046	0.358+0.028 −0.026	19.1+7.9 −8.5°	—

See also

• HD 147018
• HD 204313
• List of extrasolar planets