HD 180902

HD 180902
Observation data
Epoch J2000.0      Equinox ICRS
Constellation Sagittarius
Right ascension 19h 19m 17.708s
Declination −23° 33′ 29.36″
Apparent magnitude (V) 7.785
Characteristics
Evolutionary stage red giant branch
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
Distance342 ± 2 ly
(104.9 ± 0.6 pc)
Absolute magnitude (MV)2.5±0.3
Orbit
PrimaryHD 180902 A
SecondaryHD 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
Mass1.698±0.085 M☉
Radius4.247±0.212 R☉
Luminosity9.4±0.5 L☉
Temperature5,030±44 K
Metallicity [Fe/H]0.04±0.03 dex
Age2.8±0.7 Gyr
HD 180902 B
Mass44.53+12.91
−5.88 MJup
Other designations
CD−23°15276, HD 180902, HIP 94951, SAO 187961, PPM 269620
Database references
SIMBADdata

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.

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.

Companions

HD 180902 b was discovered using the Doppler spectroscopy method with observations taken at the W. M. Keck Observatory. The radial velocities showed a long term linear trend in the data indicating an additional companion of unknown nature with a longer orbital period. This was subsequently shown to be due to an orbiting brown dwarf or low mass stellar companion, designated component B.

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.

The HD 180902 planetary system
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

  1. ↑ Roman, Nancy G. (1987). "Identification of a constellation from a position". Publications of the Astronomical Society of the Pacific. 99 (617): 695. Bibcode:1987PASP...99..695R. doi:10.1086/132034. Constellation record for this object at VizieR.
  2. 1 2 3 4 5 6 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.
  3. 1 2 3 4 5 6 7 8 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.
  4. 1 2 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.
  5. 1 2 3 4 5 6 7 8 9 10 11 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.
  6. 1 2 3 4 5 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.
  7. ↑ "HD 180902". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-09-21.