Astronomy:HD 180902
| Observation data Equinox J2000.0]] (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[2] mas/yr Dec.: −20.334[2] mas/yr |
| Parallax (π) | 9.5339 ± 0.0521[2] mas |
| Distance | 342 ± 2 ly (104.9 ± 0.6 pc) |
| Absolute magnitude (MV) | 2.5±0.3[5] |
| Orbit[6] | |
| Primary | HD 180902 A |
| Companion | HD 180902 B |
| Period (P) | 5880±440 d |
| Semi-major axis (a) | 7.15±0.69 astronomical unit|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 | |
| 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.[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.
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 | — | — |
References
- ↑ Roman, Nancy G. (1987). "Identification of a constellation from a position". Publications of the Astronomical Society of the Pacific 99 (617): 695. doi:10.1086/132034. Bibcode: 1987PASP...99..695R Constellation record for this object at VizieR.
- ↑ 2.0 2.1 2.2 2.3 2.4 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940 Gaia DR3 record for this source at VizieR.
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 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, doi:10.1051/0004-6361/201834371, A72, Bibcode: 2019A&A...623A..72K.
- ↑ 4.0 4.1 Houk, N.; Smith-Moore, M. (1988). Michigan Catalogue of Two-dimensional Spectral Types for the HD Stars. Declinations -26°.0 to -12°.0. 4. Bibcode: 1988mcts.book.....H.
- ↑ 5.00 5.01 5.02 5.03 5.04 5.05 5.06 5.07 5.08 5.09 5.10 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. doi:10.1086/653809. Bibcode: 2010PASP..122..701J.
- ↑ 6.0 6.1 6.2 6.3 6.4 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. doi:10.3847/1538-3881/aaf5d0. Bibcode: 2019AJ....157..149L.
- ↑ "HD 180902". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=HD+180902.
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