Psi2 Aurigae

Psi2 Aurigae, Latinized from ψ2 Aurigae, is a star in the constellation Auriga. It is faintly visible to the naked eye with an apparent visual magnitude of 4.79.[2] Based upon parallax measurements, this star is approximately 420 light-years (130 parsecs) away from the Earth. At that distance, the brightness of the star is diminished by 0.07 in magnitude from extinction caused by interstellar gas and dust.[5]

For other stars with this Bayer designation, see ψ Aurigae.
Psi2 Aurigae
Location of ψ2 Aurigae (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Auriga
Right ascension 06h 39m 19.82634s[1]
Declination +42° 29′ 19.9617″[1]
Apparent magnitude (V) 4.79[2]
Characteristics
Spectral type K3 III[3] or K3 Iab:[4]
U−B color index +1.30[2]
B−V color index +1.23[2]
R−I color index 0.6
Astrometry
Radial velocity (Rv)16.09 ± 0.19[5] km/s
Proper motion (μ) RA: -0.87[1] mas/yr
Dec.: -54.97[1] mas/yr
Parallax (π)7.84 ± 0.29[1] mas
Distance420 ± 20 ly
(128 ± 5 pc)
Absolute magnitude (MV)−0.72[6]
Details
Radius27[7] R☉
Luminosity304[6] L☉
Surface gravity (log g)2.30[8] cgs
Temperature4,410[8] K
Metallicity [Fe/H]–0.10[8] dex
Rotational velocity (v sin i)1.0[9] km/s
Other designations
ψ2 Aur, 50 Aurigae, BD+42 1585, HD 47174, HIP 31832, HR 2427, SAO 41239.[10]
Database references
SIMBADdata

Most studies categorized this as a K-type giant star with a stellar classification of K3 III.[3] However, the results of a study published in 2003 list it with a classification of K3 Iab:, which would instead suggest it is a supergiant star.[4][10] The measured angular diameter of this star, after correction for limb darkening, is 1.97 ± 0.02 mas.[11] At the estimated distance of this star,[1] this yields a physical size of about 27 times the radius of the Sun.[7] It is radiating 304[6] times the Sun's luminosity from its enlarged photosphere at an effective temperature of 4,410 K.[8]

It was also known to be part of a much bigger constellation named Telescopium Herschelii. It was also the constellation's brightest star before it was unrecognized by the International Astronomical Union (IAU).

References
  1. van Leeuwen, Floor (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752v1, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357. Note: see VizieR catalogue I/311.
  2. Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99): 99, Bibcode:1966CoLPL...4...99J.
  3. Herbig, George H.; Spalding, John F., Jr. (January 1955), "Axial Rotation and Line Broadening in Stars of Spectral Types F0-K5", Astrophysical Journal, 121: 118, Bibcode:1955ApJ...121..118H, doi:10.1086/145969.
  4. Kidger, Mark R.; Martín-Luis, Fabiola (June 2003), "High-Precision Near-Infrared Photometry of a Large Sample of Bright Stars Visible from the Northern Hemisphere", The Astronomical Journal, 125 (6): 3311–3333, Bibcode:2003AJ....125.3311K, doi:10.1086/374996.
  5. Famaey, B.; et al. (January 2005), "Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters", Astronomy and Astrophysics, 430 (1): 165–186, arXiv:astro-ph/0409579, Bibcode:2005A&A...430..165F, doi:10.1051/0004-6361:20041272.
  6. 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.
  7. Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, 1 (3rd ed.), Birkhäuser, ISBN 3-540-29692-1. The radius (R*) is given by:
  8. McWilliam, Andrew (December 1990), "High-resolution spectroscopic survey of 671 GK giants. I - Stellar atmosphere parameters and abundances", Astrophysical Journal Supplement Series, 74: 1075–1128, Bibcode:1990ApJS...74.1075M, doi:10.1086/191527.
  9. De Medeiros, J. R.; et al. (November 2000), "Rotation and lithium in single giant stars", Astronomy and Astrophysics, 363: 239–243, arXiv:astro-ph/0010273, Bibcode:2000A&A...363..239D.
  10. "* 50 Aur". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 24 March 2016.
  11. Richichi, A.; Percheron, I.; Khristoforova, M. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics, 431 (2): 773–777, Bibcode:2005A&A...431..773R, doi:10.1051/0004-6361:20042039.
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