Chi Geminorum

Chi Geminorum (χ Gem) is a binary star system in the constellation Gemini, near the western border with Cancer. It can be viewed with the naked eye on a dark night, having an apparent visual magnitude of 4.98.[2] Based upon an annual parallax shift of 12.73 mas,[1] it is located roughly 260 light years from the Sun.

χ Geminorum
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Gemini
Right ascension 08h 03m 31.08225s[1]
Declination +27° 47′ 39.6243″[1]
Apparent magnitude (V) 4.98[2]
Characteristics
Spectral type K2 III[3]
U−B color index +1.09[2]
B−V color index +1.14[2]
Astrometry
Radial velocity (Rv)−3.83±0.17[4] km/s
Proper motion (μ) RA: −25.52[1] mas/yr
Dec.: -31.89[1] mas/yr
Parallax (π)12.73 ± 0.90[1] mas
Distance260 ± 20 ly
(79 ± 6 pc)
Absolute magnitude (MV)0.461[5]
Orbit[6]
Period (P)2,437.8d
Eccentricity (e)0.06
Periastron epoch (T)2442894.5 ± 10.0 JD
Argument of periastron (ω)
(secondary)		264°
Semi-amplitude (K1)
(primary)		5.2 km/s
Details[4]
Mass1.83[3] M☉
Radius14 R☉
Luminosity79 L☉
Surface gravity (log g)2.5 cgs
Temperature4,560±5 K
Metallicity [Fe/H]0.03 dex
Rotational velocity (v sin i)3.8 km/s
Age1.92[3] Gyr
Other designations
χ Gem, BD+28° 1532, FK5 305, HD 66216, HIP 39424, HR 3149, SAO 79896.[7]
Database references
SIMBADdata

The two components of this system form a spectroscopic binary with an orbital period of 2,437.8 days and an eccentricity of 0.06.[6] The primary component is a K-type giant star with a stellar classification of K2 III.[3] This is a candidate mild Barium star with the slight overabundance most likely acquired through accretion from what is now a white dwarf companion.[8] The primary has an estimated 1.83[3] times the mass of the Sun and has expanded to 14 times the Sun's radius.[4] The effective temperature of the outer atmosphere is 4,560 K, from whence it radiates 79 times the solar luminosity.[4] It has a leisurely projected rotational velocity of 3.8[4] km/s and is around two billion years old.[3]

References
  1. van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357.
  2. Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV Data, SIMBAD, Bibcode:1986EgUBV........0M.
  3. Luck, R. Earle (September 2015), "Abundances in the Local Region. I. G and K Giants", The Astronomical Journal, 150 (3): 23, arXiv:1507.01466, Bibcode:2015AJ....150...88L, doi:10.1088/0004-6256/150/3/88, 88.
  4. Massarotti, Alessandro; et al. (January 2008), "Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity", The Astronomical Journal, 135 (1): 209–231, Bibcode:2008AJ....135..209M, doi:10.1088/0004-6256/135/1/209.
  5. Soubiran, C.; et al. (March 2008), "Vertical distribution of Galactic disk stars. IV. AMR and AVR from clump giants", Astronomy and Astrophysics, 480 (1): 91–101, arXiv:0712.1370, Bibcode:2008A&A...480...91S, doi:10.1051/0004-6361:20078788.
  6. Pourbaix, D.; et al. (2004), "SB9: The ninth catalogue of spectroscopic binary orbits", Astronomy & Astrophysics, 424 (2): 727, arXiv:astro-ph/0406573, Bibcode:2004A&A...424..727P, doi:10.1051/0004-6361:20041213.
  7. "* chi Gem". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2016-12-09.
  8. Yang, Guo-Chao; et al. (January 2016), "Chemical abundance analysis of 19 barium stars", Research in Astronomy and Astrophysics, 16 (1), arXiv:1602.08704, Bibcode:2016RAA....16...19Y, doi:10.1088/1674-4527/16/1/019, 19.
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