2 Aurigae

2 Aurigae is a possible binary star system in the northern constellation of Auriga. This object is visible to the naked eye as a faint, orange-hued star with an apparent visual magnitude of +4.79.[2] It forms an attractive four-star asterism when viewed in a low power eyepiece, together with the nearby HIP 22647 and another very loose visual pair, HIP 22776 and HIP 22744, all above magnitude 8. 2 Aurigae is moving closer to the Earth with a heliocentric radial velocity of −17 km/s.[4]

2 Aurigae
Location of 2 Aurigae (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Auriga
Right ascension  04h 52m 37.98097s[1]
Declination +36° 42′ 11.4789″[1]
Apparent magnitude (V) +4.79[2]
Characteristics
Spectral type K3- III Ba0.4[3]
B−V color index 1.414±0.003[4]
Astrometry
Radial velocity (Rv)−17.24±0.08[4] km/s
Proper motion (μ) RA: −25.731[1] mas/yr
Dec.: −3.867[1] mas/yr
Parallax (π)6.3340 ± 0.2695[1] mas
Distance510 ± 20 ly
(158 ± 7 pc)
Absolute magnitude (MV)–1.84[2]
Details
Mass2.86[5] M☉
Radius48.14+0.83
−1.79[1] R☉
Luminosity599±29[1] L☉
Surface gravity (log g)1.79[6] cgs
Temperature4,115+79
−35[1] K
Metallicity [Fe/H]−0.24±0.03[4] dex
Rotational velocity (v sin i)2.3[6] km/s
Age1.80[5] Gyr
Other designations
2 Aur, BD+36°952, FK5 1201, HD 30834, HIP 22678, HR 1551, SAO 57475[7]
Database references
SIMBADdata
2 Aurigae in optical light

The visible component is an aging giant star with a stellar classification of K3- III Ba0.4.[3] The suffix notation indicates this is a mild barium star, which means the stellar atmosphere is enriched with s-process elements. It is either a member of a close binary system and has previously acquired these elements from a (now) white dwarf companion or else it is on the asymptotic giant branch and is generating the elements itself.[8] 2 Aurigae is 1.80[5] billion years old with 2.86[5] times the mass of the Sun and has expanded to 48[1] times the Sun's radius. It is radiating 599[1] times the Sun's luminosity from its enlarged photosphere at an effective temperature of 4,115 K.[1]

References
  1. 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. Jasniewicz, G.; et al. (February 1999), "Late-type giants with infrared excess. I. Lithium abundances", Astronomy and Astrophysics, 342: 831–838, Bibcode:1999A&A...342..831J
  3. Keenan, Philip C.; McNeil, Raymond C. (1989), "The Perkins catalog of revised MK types for the cooler stars", Astrophysical Journal Supplement Series, 71: 245, Bibcode:1989ApJS...71..245K, doi:10.1086/191373.
  4. 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.
  5. Luck, R. Earle (2015), "Abundances in the Local Region. I. G and K Giants", Astronomical Journal, 150 (3), 88, arXiv:1507.01466, Bibcode:2015AJ....150...88L, doi:10.1088/0004-6256/150/3/88.
  6. Takeda, Y.; Tajitsu, A. (August 2017), "On the observational characteristics of lithium-enhanced giant stars in comparison with normal red giants", Publications of the Astronomical Society of Japan, 69 (4): 978–88, arXiv:1706.02273, Bibcode:2017PASJ...69...74T, doi:10.1093/pasj/psx057.
  7. "2 Aur". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-04-03.
  8. Gomez, A. E.; et al. (1997), "Absolute magnitudes and kinematics of barium stars", Astronomy and Astrophysics, 319: 881, Bibcode:1997A&A...319..881G.
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