# Psi2 Aurigae

Observation data Epoch J2000      Equinox J2000 Constellation Location of ψ2 Aurigae (circled) Auriga 06h 39m 19.82634s[1] +42° 29′ 19.9617″[1] 4.79[2] K3 III[3] or K3 Iab:[4] +1.30[2] +1.23[2] 0.6 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 Distance 420 ± 20 ly (128 ± 5 pc) Absolute magnitude (MV) −0.72[6] Radius 27[7] R☉ Luminosity 304[6] L☉ Surface gravity (log g) 2.30[8] cgs Temperature 4,410[8] K Metallicity [Fe/H] –0.10[8] dex Rotational velocity (v sin i) 1.0[9] km/s ψ2 Aur, 50 Aurigae, BD+42 1585, HD 47174, HIP 31832, HR 2427, SAO 41239.[10] SIMBAD data

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]

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]

## 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. ^ a b c d 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. ^ a b 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. ^ a b 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. ^ a b 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. ^ a b c 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. ^ a b 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:
{\displaystyle {\begin{aligned}2\cdot R_{*}&={\frac {(128\cdot 1.97\cdot 10^{-3})\ {\text{AU}}}{0.0046491\ {\text{AU}}/R_{\bigodot }}}\\&\approx 54\cdot R_{\bigodot }\end{aligned}}}
8. ^ a b c d 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. ^ a b "* 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.