HD 171238
Star in the constellation Sagittarius From Wikipedia, the free encyclopedia
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]
| 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 | |
| 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]
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 MJ; higher than the minimum mass estimated from Doppler spectroscopy.[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° |
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