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81 Geminorum

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81 Geminorum
Location of 81 Geminorum (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Gemini
Right ascension 07h 46m 07.45014s[1]
Declination +18° 30′ 36.0217″[1]
Apparent magnitude (V) 4.89[2]
Characteristics
Spectral type K4 III[3]
B−V color index 1.425±0.034[2]
Astrometry
Radial velocity (Rv)+83.13±0.08[2] km/s
Proper motion (μ) RA: −79.687[1] mas/yr
Dec.: −53.551[1] mas/yr
Parallax (π)9.1500 ± 0.2963 mas[1]
Distance360 ± 10 ly
(109 ± 4 pc)
Absolute magnitude (MV)−0.19[2]
Orbit[4]
Period (P)1,519.7±1.7 d
Semi-major axis (a)≥ 142±3 Gm
Eccentricity (e)0.325±0.015
Periastron epoch (T)41,584±11 MJD
Argument of periastron (ω)
(secondary)		73±3°
Semi-amplitude (K1)
(primary)		7.21±0.13 km/s
Details
81 Gem A
Mass1.22[5] M☉
Radius33.7+2.0
−1.7[1] R☉
Luminosity287.3±10.5[1] L☉
Surface gravity (log g)1.94[6] cgs
Temperature4,095+109
−115[1] K
Metallicity [Fe/H]−0.18±0.06[2] dex
Age6.32[5] Gyr
Other designations
g Gem, 81 Gem, BD+18°1733, FK5 1200, GC 10456, HD 62721, HIP 37908, HR 3003, SAO 97221, WDS J07461+1831AB[7]
Database references
SIMBADdata

81 Geminorum is a binary star[8] system in the northern constellation of Gemini. It has the Bayer designation g Geminorum, while 81 Geminorum is its Flamsteed designation. This system is visible to the naked eye as a faint, orange-hued point of light with an apparent visual magnitude of 4.89.[2] The pair are located approximately 360 light years away from the Sun, based on parallax,[1] and are moving further away with a radial velocity of +83 km/s, having come to within an estimated 164 light-years of the Earth nearly a million years ago.[2] 81 Geminorum lies close enough to the ecliptic to undergo lunar occultations.[4][9]

The variable velocity of this system was first suspected at the Dominion Astrophysical Observatory in 1921, then confirmed by the Lick Observatory in 1922. It is a single-lined spectroscopic binary with an orbital period of 4.2 years and an eccentricity of 0.325.[4] The visible component is an aging giant star with a stellar classification of K4 III,[3] having exhausted the supply of hydrogen at its core then expanded to 34[1] times the Sun's radius. It is over six[5] billion years old with 1.22[5] times the mass of the Sun. This is a candidate alpha-enhanced star that displays a significant overabundance of silicon.[10] The star is radiating around 287[1] times the Sun's luminosity from its bloated photosphere at an effective temperature of 4,095 K.[1]

References

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  1. ^ a b c d e f g h i j k l Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. ^ a b c d e f g Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015, S2CID 119257644.
  3. ^ a b Keenan, P.; McNeil, R. (October 1989), "The Perkins catalog of revised MK types for the cooler stars", Astrophysical Journal Supplement Series, 71: 245–266, Bibcode:1989ApJS...71..245K, doi:10.1086/191373.
  4. ^ a b c Griffin, R. F. (September 1982), "Photoelectric radial velocities. Paper IX. The orbits of the spectroscopic binaries 81 and chi Gem", Monthly Notices of the Royal Astronomical Society, 200: 1161–1168, Bibcode:1982MNRAS.200.1161G, doi:10.1093/mnras/200.4.1161.
  5. ^ a b c d Luck, R. Earle (2015), "Abundances in the Local Region. I. G and K Giants", The Astronomical Journal, 150 (3): 88, arXiv:1507.01466, Bibcode:2015AJ....150...88L, doi:10.1088/0004-6256/150/3/88, S2CID 118505114.
  6. ^ Prugniel, Ph.; et al. (July 2011), "The atmospheric parameters and spectral interpolator for the MILES stars", Astronomy & Astrophysics, 531: A165, arXiv:1104.4952, Bibcode:2011A&A...531A.165P, doi:10.1051/0004-6361/201116769, S2CID 54940439.
  7. ^ "81 Gem". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 19 August 2017.
  8. ^ Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x, S2CID 14878976.
  9. ^ Cassar, L.; et al. (March 1989), "Lunar Occultations of IRAS Point Sources, 1991--2000", Astrophysical Journal Supplement, 69: 651, Bibcode:1989ApJS...69..651C, doi:10.1086/191323.
  10. ^ Franchini, M.; et al. (2004). "Synthetic Lick Indices and Detection of α-enhanced Stars. II. F, G, and K Stars in the -1.0 < [Fe/H] < +0.50 Range". The Astrophysical Journal. 613 (1): 312. Bibcode:2004ApJ...613..312F. doi:10.1086/422909. S2CID 250877375.
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