| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Sagittarius |
| Right ascension | 19h 19m 17.708s[1] |
| Declination | −23° 33′ 29.36″[1] |
| Apparent magnitude (V) | 7.785[2] |
| Characteristics | |
| Spectral type | K0 III/IV[3] |
| B−Vcolor index | +0.94[4] |
| Astrometry | |
| Radial velocity (Rv) | −2.781±0.140[2] km/s |
| Proper motion (μ) | RA: 37.832mas/yr[1] Dec.: −20.334mas/yr[1] |
| Parallax (π) | 9.5339±0.0521 mas[1] |
| Distance | 342 ± 2 ly (104.9 ± 0.6 pc) |
| Absolute magnitude (MV) | 2.5±0.3[4] |
| Orbit[5] | |
| Primary | HD 180902 A |
| Companion | HD 180902 B |
| Period (P) | 5880±440 d |
| Semi-major axis (a) | 7.15±0.69 AU |
| Eccentricity (e) | 0.335±0.025 |
| Periastronepoch (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[2] M☉ |
| Radius | 4.247±0.212[2] R☉ |
| Luminosity | 9.4±0.5[4] L☉ |
| Temperature | 5,030±44[4] K |
| Metallicity[Fe/H] | 0.04±0.03[4] dex |
| Age | 2.8±0.7[4] Gyr |
| HD 180902 B | |
| Mass | 44.53+12.91 −5.88[2] MJup |
| Other designations | |
| CD−23° 15276,HD 180902,HIP 94951,SAO 187961,PPM 269620[6] | |
| Database references | |
| SIMBAD | data |
HD 180902 is astar with two or more orbiting companions in the southernconstellation ofSagittarius. This system is located at a distance of approximately 342 light years from the Sun based onparallax measurements, but is drifting closer with aradial velocity of −2.8 km/s.[2] It has anabsolute magnitude of 2.5,[4] but at that distance theapparent visual magnitude of the system is 7.8,[2] which is too faint to be seen with the naked eye.
Thespectrum of the primary, component A, presents as anevolvingsubgiant star[5] with astellar classification of K0 III/IV.[3] It is an estimated 2.8[4] 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[2] and is radiating 9.4 times the Sun's luminosity from an enlargedphotosphere at aneffective temperature of 5,030 K.[4]
HD 180902 b was discovered using theDoppler spectroscopy method with observations taken at theW. M. Keck Observatory.[4] The radial velocities showed a long term linear trend in the data indicating an additional companion of unknown nature with a longer orbital period.[4] This was subsequently shown to be due to an orbitingbrown dwarf or low mass stellar companion, designated component B.[5]
There is a second unconfirmed planet, HD 180902 c, with a mass at least twice that ofNeptune and an orbital period of 15 days.[5]
| 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±0.014MJ | 0.139±0.011 | 15.9058±0.0055 | 0.28±0.13 | — | — |
