81 Geminorum

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]

  1. ^ a b c d e f g h i j k l Cite error: The named reference GaiaDR2 was invoked but never defined (see the help page).
  2. ^ a b c d e f g Cite error: The named reference Anderson2012 was invoked but never defined (see the help page).
  3. ^ a b Cite error: The named reference Keenan1989 was invoked but never defined (see the help page).
  4. ^ a b c Cite error: The named reference Griffin1982 was invoked but never defined (see the help page).
  5. ^ a b c d Cite error: The named reference luck2015 was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference Prugniel2011 was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference Eggleton2008 was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference Cassar1989 was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference Franchini2004 was invoked but never defined (see the help page).