| 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−V color index | +0.94 [4] |
| Astrometry | |
| Radial velocity (Rv) | −2.781±0.140 [2] km/s |
| Proper motion (μ) |
RA: 37.832
mas/
yr
[1] Dec.: −20.334 mas/ 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 |
| 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 [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 | |
| Database references | |
| SIMBAD | data |
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. [2] It has an absolute magnitude of 2.5, [4] but at that distance the apparent visual magnitude of the system is 7.8, [2] which is too faint to be seen with the naked eye.
The spectrum of the primary, component A, presents as an evolving subgiant star [5] with a stellar 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 enlarged photosphere at an effective temperature of 5,030 K. [4]
Companions
HD 180902 b was discovered using the Doppler spectroscopy method with observations taken at the W. 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 orbiting brown 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 of Neptune 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±0.014 MJ | 0.139±0.011 | 15.9058±0.0055 | 0.28±0.13 | — | — |
References
- ^ a b c d Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv: 2208.00211. Bibcode: 2023A&A...674A...1G. doi: 10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
- ^ a b c d e f g h Kervella, Pierre; et al. (March 2019), "Stellar and substellar companions of nearby stars from Gaia DR2. Binarity from proper motion anomaly", Astronomy & Astrophysics, 623: 23, arXiv: 1811.08902, Bibcode: 2019A&A...623A..72K, doi: 10.1051/0004-6361/201834371, S2CID 119491061, A72.
- ^ a b Houk, N.; Smith-Moore, M. (1988). Michigan Catalogue of Two-dimensional Spectral Types for the HD Stars. Declinations -26°.0 to -12°.0. Vol. 4. Bibcode: 1988mcts.book.....H.
- ^ a b c d e f g h i j k Johnson, John Asher; et al. (2010). "Retired A Stars and Their Companions. IV. Seven Jovian Exoplanets from Keck Observatory". Publications of the Astronomical Society of the Pacific. 122 (892): 701–711. arXiv: 1003.3445. Bibcode: 2010PASP..122..701J. doi: 10.1086/653809.
- ^ a b c d e Luhn, Jacob K.; et al. (2019). "Retired A Stars and Their Companions. VIII. 15 New Planetary Signals around Subgiants and Transit Parameters for California Planet Search Planets with Subgiant Hosts". The Astronomical Journal. 157 (4). 149. arXiv: 1811.03043. Bibcode: 2019AJ....157..149L. doi: 10.3847/1538-3881/aaf5d0. S2CID 102486961.
- ^ "HD 180902". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-09-21.
