Upsilon Aurigae

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Upsilon Aurigae
Diagram showing star positions and boundaries of the Auriga constellation and its surroundings
Cercle rouge 100%.svg

The location of υ Aurigae (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Auriga
Right ascension 05h 51m 02.43724s[1]
Declination +37° 18′ 20.0565″[1]
Apparent magnitude (V) 4.74[2]
Spectral type M0 III[3]
U−B color index +1.93[2]
B−V color index +1.62[2]
R−I color index 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
Other designations
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]


  1. ^ a b c d e f 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 (3rd 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}
  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. 

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