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

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]

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 $M$ _J	2.518+0.032 −0.033	4.148+0.045 −0.046	0.358+0.028 −0.026	19.1+7.9 −8.5°	—

References

^ ^a ^b ^c ^d Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
^ ^a ^b Nordström, B.; et al. (May 2004), "The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of ˜14 000 F and G dwarfs", Astronomy and Astrophysics, 418: 989–1019, arXiv:astro-ph/0405198, Bibcode:2004A&A...418..989N, doi:10.1051/0004-6361:20035959, S2CID 11027621.
^ ^a ^b Houk, Nancy (1979), Michigan catalogue of two-dimensional spectral types for the HD stars, vol. 3, Ann Arbor, Michigan: Dept. of Astronomy, University of Michigan, Bibcode:1982mcts.book.....H.
^ ^a ^b ^c Cutri, R. M.; et al. (June 2003), 2MASS All Sky Catalog of point sources, NASA/IPAC, Bibcode:2003tmc..book.....C
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ Ségransan, D.; et al. (2009), "The CORALIE survey for southern extrasolar planets. XVI. Discovery of a planetary system around HD 147018 and of two long period and massive planets orbiting HD 171238 and HD 204313", Astronomy & Astrophysics, 511: A45, arXiv:0908.1479, Bibcode:2010A&A...511A..45S, doi:10.1051/0004-6361/200912136, S2CID 8864844.
^ ^a ^b Soubiran, C.; et al. (2018), "Gaia Data Release 2. The catalogue of radial velocity standard stars", Astronomy and Astrophysics, 616: A7, arXiv:1804.09370, Bibcode:2018A&A...616A...7S, doi:10.1051/0004-6361/201832795, S2CID 52952408.
^ ^a ^b ^c ^d ^e ^f ^g ^h Bonfanti, A.; et al. (2016), "Age consistency between exoplanet hosts and field stars", Astronomy & Astrophysics, 585: 14, arXiv:1511.01744, Bibcode:2016A&A...585A...5B, doi:10.1051/0004-6361/201527297, S2CID 53971692, A5.
^ "HD 171238". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2023-12-30.
^ ^a ^b Li, Yiting; et al. (2021), "Precise Masses and Orbits for Nine Radial-velocity Exoplanets", The Astronomical Journal, 162 (6): 266, arXiv:2109.10422, Bibcode:2021AJ....162..266L, doi:10.3847/1538-3881/ac27ab, S2CID 237592581.