HD 180902
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. It has an absolute magnitude of 2.5, but at that distance the apparent visual magnitude of the system is 7.8, which is too faint to be seen with the naked eye.
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Sagittarius |
| Right ascension | 19h 19m 17.708s |
| Declination | −23° 33′ 29.36″ |
| Apparent magnitude (V) | 7.785 |
| Characteristics | |
| Spectral type | K0 III/IV |
| B−V color index | +0.94 |
| Astrometry | |
| Radial velocity (Rv) | −2.781±0.140 km/s |
| Proper motion (μ) | RA: 37.832 mas/yr Dec.: −20.334 mas/yr |
| Parallax (π) | 9.5339 ± 0.0521 mas |
| Distance | 342 ± 2 ly (104.9 ± 0.6 pc) |
| Absolute magnitude (MV) | 2.5±0.3 |
| Orbit | |
| 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 |
| 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 M☉ |
| Radius | 4.247±0.212 R☉ |
| Luminosity | 9.4±0.5 L☉ |
| Temperature | 5,030±44 K |
| Metallicity [Fe/H] | 0.04±0.03 dex |
| Age | 2.8±0.7 Gyr |
| HD 180902 B | |
| Mass | 44.53+12.91 −5.88 MJup |
| Other designations | |
| Database references | |
| SIMBAD | data |
The spectrum of the primary, component A, presents as an evolving subgiant star with a stellar classification of K0 III/IV. It is an estimated 2.8 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 and is radiating 9.4 times the Sun's luminosity from an enlarged photosphere at an effective temperature of 5,030 K.