# Upsilon Aurigae

Observation data Constellation Epoch J2000      Equinox J2000 The location of υ Aurigae (circled) Auriga 05h 51m 02.43724s[1] +37° 18′ 20.0565″[1] 4.74[2] M0 III[3] +1.93[2] +1.62[2] 1.07 Radial velocity (Rv) +37.68[4] km/s Proper motion (μ) RA: +36.85[1] mas/yr Dec.: -45.52[1] mas/yr Parallax (π) 6.24 ± 0.65[1] mas Distance approx. 520 ly (approx. 160 pc) Radius 73[5] R☉ 31 Aurigae, BD+37 1336, FK5 2440, HD 38944, HIP 27639, HR 2011, SAO 58496.[6]

Upsilon Aurigae (υ Aur, υ Aurigae) is the Bayer designation for a star in the northern constellation of Auriga. It has an apparent visual magnitude of 4.74,[2] which means it is bright enough to be seen with the naked eye. Based upon parallax measurements made during the Hipparcos mission, this star is approximately 520 light-years (160 parsecs) distant from the Earth.

This is an evolved red giant star with a stellar classification of M0 III.[3] It is a suspected variable star[7] and is currently on the asymptotic giant branch, which means it is generating energy at its core through the fusion of helium.[8] The measured angular diameter of this star, after correction for limb darkening, is 4.24 ± 0.05 mas.[9] At the estimated distance of Upsilon Aurigae,[1] this yields a physical size of about 73 times the radius of the Sun.[5]

## 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 Keenan, Philip C.; Barnbaum, Cecilia (June 1999), "Revision and Calibration of MK Luminosity Classes for Cool Giants by HIPPARCOS Parallaxes", The Astrophysical Journal 518 (2): 859–865, Bibcode:1999ApJ...518..859K, doi:10.1086/307311.
4. ^ 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.
5. ^ 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{(160\cdot 4.24 \cdot 10^{-3})\ \text{AU}}{0.0046491\ \text{AU}/R_{\bigodot}} \\ & \approx 146\cdot R_{\bigodot} \end{align}
6. ^ "ups Aur -- Variable Star", SIMBAD Astronomical Database (Centre de Données astronomiques de Strasbourg), retrieved 2012-08-23.
7. ^ Hamada, K. et al. (January 1979), "On the Variability of upsilon Aurigae", Information Bulletin on Variable Stars 1531: 1, Bibcode:1979IBVS.1531....1H.
8. ^ Eggen, Olin J. (July 1992), "Asymptotic giant branch stars near the sun", Astronomical Journal 104 (1): 275–313, Bibcode:1992AJ....104..275E, doi:10.1086/116239.
9. ^ 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.