HD 171238
Star in the constellation Sagittarius
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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.[7] The star has an absolute magnitude of 5.15,[6] 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.[3]
| Observation data Epoch J2000.0 Equinox ICRS | |
|---|---|
| Constellation | Sagittarius[1] |
| Right ascension | 18h 34m 43.676s[2] |
| Declination | −28° 04′ 20.33″[2] |
| Apparent magnitude (V) | 8.606[3] |
| Characteristics | |
| Evolutionary stage | main sequence[2] |
| Spectral type | G8 V[4] |
| Apparent magnitude (B) | 9.40 |
| Apparent magnitude (J) | 7.244[5] |
| Apparent magnitude (H) | 6.868[5] |
| Apparent magnitude (K) | 6.831[5] |
| B−V color index | 0.74[6] |
| Astrometry | |
| Radial velocity (Rv) | 21.11±0.17[7] km/s |
| Proper motion (μ) | RA: −29.539 mas/yr[2] Dec.: −109.580 mas/yr[2] |
| Parallax (π) | 22.4809±0.0324 mas[2] |
| Distance | 145.1 ± 0.2 ly (44.48 ± 0.06 pc) |
| Absolute magnitude (MV) | 5.15[6] |
| Details | |
| Mass | 0.99±0.01[8] M☉ |
| Radius | 0.95±0.01[8] R☉ |
| Luminosity | 0.774±0.003[8] L☉ |
| Surface gravity (log g) | 4.47±0.01[8] cgs |
| Temperature | 5,570±21[8] K |
| Metallicity [Fe/H] | 0.17±0.007[6] dex |
| Rotational velocity (v sin i) | 1.48[6] km/s |
| Age | 4.0±1.2[8] Gyr |
| Other designations | |
| CD−28°14719, HD 171238, HIP 91085, SAO 186998, PPM 268605[9] | |
| 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.[4] At an estimated age of around four billion years,[8] it is spinning with a projected rotational velocity of 1.5 km/s.[6] The metallicity of the star – the abundance of elements more massive than helium – is 48% higher than solar, based on the abundance of iron.[6] There are indications of a significant level of magnetic activity in the chromosphere.[6] 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.[8]
Planetary system
In August 2009, it was announced that this star has a super-jovian exoplanet.[6] Using astrometry from Gaia, astronomers were able to deduce the true mass of HD 171238 b as 8.8 MJ; higher than the minimum mass estimated from Doppler spectroscopy.[10]
| 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 |
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