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HD 154857 is a star with two exoplanetary companions in the southern constellation of Ara. It is too dim to be visible with the naked eye having an apparent visual magnitude of 7.25.[2] The star is located at a distance of 207 light years from the Sun based on parallax measurements, and is drifting further away with a radial velocity of +28 km/s.[1]
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Ara |
| Right ascension | 17h 11m 15.72180s[1] |
| Declination | −56° 40′ 50.8706″[1] |
| Apparent magnitude (V) | 7.25[2] |
| Characteristics | |
| Spectral type | G5IV-V[3] |
| B−V color index | 0.699±0.001[2] |
| Variable type | Constant[4] |
| Astrometry | |
| Radial velocity (Rv) | +28.06±0.15[1] km/s |
| Proper motion (μ) | RA: 87.585[1] mas/yr Dec.: −55.891[1] mas/yr |
| Parallax (π) | 15.7321 ± 0.0385 mas[1] |
| Distance | 207.3 ± 0.5 ly (63.6 ± 0.2 pc) |
| Absolute magnitude (MV) | 3.07[3] |
| Details | |
| Mass | 1.718+0.03 −0.022[5] M☉ |
| Radius | 2.1±0.1[4] R☉ |
| Luminosity | 4.4±0.3[4] L☉ |
| Surface gravity (log g) | 3.83±0.03[4] cgs |
| Temperature | 5,740±46[4] K |
| Metallicity [Fe/H] | −0.26±0.01[6] dex |
| Rotational velocity (v sin i) | 1.44±0.50[7] km/s |
| Age | 5.8±0.5[4] Gyr |
| Other designations | |
| Database references | |
| SIMBAD | data |
This is a G-type star with a stellar classification of G5IV-V.[3] The absolute magnitude of this star is two magnitudes above the main sequence, which suggests that the star is evolving toward the subgiant stage.[3] It is a metal-poor thin disk star[9] approximately six billion years old and is chromopherically quiet although not in a Maunder Minimum state.[4] The star is larger, more massive, and more luminous than the Sun. It is spinning with a projected rotational velocity of 1.4 km/s.[7]
The discovery of one confirmed and one unconfirmed Jovian exoplanet was reported in 2004[3] and 2007[10] respectively. The former planet HD 154857 b has mass >1.8 times that of Jupiter. It orbits the star 20% further than Earth-Sun distance, taking 409 days with 47% eccentricity. The additional object (HD 154857 c) was confirmed as a planetary companion in January 2014.[5]
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | ≥ 2.24±0.05 MJ | 1.291±0.008 | 408.6±0.5 | 0.06±0.05 | — | — |
| c | ≥ 2.58±0.16 MJ | 5.36±0.09 | 3,452±105 | 0.06±0.05 | — | — |
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