HD 180902
Star in the constellation Sagittarius
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HD 180902 is a star with two or more orbiting companions in the southern constellation of Sagittarius. This system is located at a distance of approximately 342 light years from the Sun based on parallax measurements, but is drifting closer with a radial velocity of −2.8 km/s.[3] It has an absolute magnitude of 2.5,[5] but at that distance the apparent visual magnitude of the system is 7.8,[3] which is too faint to be seen with the naked eye.
| Observation data Epoch J2000.0 Equinox ICRS | |
|---|---|
| Constellation | Sagittarius[1] |
| Right ascension | 19h 19m 17.708s[2] |
| Declination | −23° 33′ 29.36″[2] |
| Apparent magnitude (V) | 7.785[3] |
| Characteristics | |
| Evolutionary stage | red giant branch[2] |
| Spectral type | K0 III/IV[4] |
| B−V color index | +0.94[5] |
| Astrometry | |
| Radial velocity (Rv) | −2.781±0.140[3] km/s |
| Proper motion (μ) | RA: 37.832 mas/yr[2] Dec.: −20.334 mas/yr[2] |
| Parallax (π) | 9.5339±0.0521 mas[2] |
| Distance | 342 ± 2 ly (104.9 ± 0.6 pc) |
| Absolute magnitude (MV) | 2.5±0.3[5] |
| Orbit[6] | |
| Primary | HD 180902 A |
| Name | HD 180902 B |
| Period (P) | 5880±440 d |
| Semi-major axis (a) | 7.15±0.69 AU |
| Eccentricity (e) | 0.335±0.025 |
| Periastron epoch (T) | 2441100±1200 JD |
| Argument of periastron (ω) (secondary) | 73.3±1.6° |
| Semi-amplitude (K1) (primary) | 898±28 km/s |
| Details | |
| HD 180902 A | |
| Mass | 1.698±0.085[3] M☉ |
| Radius | 4.247±0.212[3] R☉ |
| Luminosity | 9.4±0.5[5] L☉ |
| Temperature | 5,030±44[5] K |
| Metallicity [Fe/H] | 0.04±0.03[5] dex |
| Age | 2.8±0.7[5] Gyr |
| HD 180902 B | |
| Mass | 44.53+12.91 −5.88[3] MJup |
| Other designations | |
| CD−23°15276, HD 180902, HIP 94951, SAO 187961, PPM 269620[7] | |
| Database references | |
| SIMBAD | data |
The spectrum of the primary, component A, presents as an evolving subgiant star[6] with a stellar classification of K0 III/IV.[4] It is an estimated 2.8[5] billion years old with 1.7 times the mass of the Sun. The star has expanded to 4.2 times the radius of the Sun[3] and is radiating 9.4 times the Sun's luminosity from an enlarged photosphere at an effective temperature of 5,030 K.[5]
Companions
HD 180902 b was discovered using the Doppler spectroscopy method with observations taken at the W. M. Keck Observatory.[5] The radial velocities showed a long term linear trend in the data indicating an additional companion of unknown nature with a longer orbital period.[5] This was subsequently shown to be due to an orbiting brown dwarf or low mass stellar companion, designated component B.[6]
There is a second unconfirmed planet, HD 180902 c, with a mass at least twice that of Neptune and an orbital period of 15 days.[6]
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination (°) |
Radius |
|---|---|---|---|---|---|---|
| b | ≥1.685±0.041 MJ | 1.40±0.11 | 510.9±1.5 | 0.107±0.022 | — | — |
| c (unconfirmed) | ≥0.099±0.014 MJ | 0.139±0.011 | 15.9058±0.0055 | 0.28±0.13 | — | — |