# Psi2 Aurigae

For other star systems with this Bayer designation, see Psi Aurigae.
Observation data Characteristics Epoch J2000      Equinox J2000 The location of ψ2 Aurigae (circled) Constellation Auriga Right ascension 06h 39m 19.82634s[1] Declination +42° 29′ 19.9617″[1] Apparent magnitude (V) 4.79[2] 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 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) Radius 27[6] R☉ Surface gravity (log g) 2.30[7] Temperature 4,410[7] K Metallicity [Fe/H] –0.10[7] dex Rotational velocity (v sin i) 1.0[8] km/s 50 Aurigae, BD+42 1585, HD 47174, HIP 31832, HR 2427, SAO 41239.[9]

Psi2 Aurigae2 Aur, 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][9] The measured angular diameter of this star, after correction for limb darkening, is 1.97 ± 0.02 mas.[10] At the estimated distance of this star,[1] this yields a physical size of about 27 times the radius of the Sun.[6]

## 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), 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....125.3311K4, 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 Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library 1 (3 ed.), Birkhäuser, ISBN 3-540-29692-1. The radius (R*) is given by:
\begin{align} 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{align}
7. ^ a b c 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.
8. ^ 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.
9. ^ a b "50 Aur -- Star in double system", SIMBAD Astronomical Database (Centre de Données astronomiques de Strasbourg), retrieved 2012-08-24.
10. ^ Richichi; Percheron, I.; Khristoforova, M. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics 431: 773–777, Bibcode:2005A&A...431..773R, doi:10.1051/0004-6361:20042039.