Sigma Aurigae

σ Aurigae
Location of σ Aurigae (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Auriga
Right ascension 05h 24m 39.14142s[1]
Declination +37° 23′ 07.2589″[1]
Apparent magnitude (V) 4.99[2]
Characteristics
Spectral type K4 III[3]
U−B color index +1.75[2]
B−V color index +1.42[2]
Astrometry
Radial velocity (Rv)–19.7[4] km/s
Proper motion (μ) RA: +0.71[5] mas/yr
Dec.: –11.51[5] mas/yr
Parallax (π)6.2101 ± 0.2221 mas[1]
Distance530 ± 20 ly
(161 ± 6 pc)
Absolute magnitude (MV)−0.75[6]
Details
Radius43.72+1.08
−3.24[1] R☉
Luminosity496±20[1] L☉
Surface gravity (log g)1.75[7] cgs
Temperature4,120+162
−50[1] K
Metallicity [Fe/H]–0.03[7] dex
Rotational velocity (v sin i)10[8] km/s
Other designations
σ Aur, 21 Aurigae, BD+37°1175, HD 35186, HIP 25292, HR 1773, SAO 57981[9]
Database references
SIMBADdata

Sigma Aurigae, Latinized from σ Aurigae, is a giant star in the northern constellation of Auriga. It is faintly visible to the naked eye with an apparent visual magnitude of 4.99.[2] With an annual parallax shift of 6.21 mas,[5] it is approximately 530 light-years (160 parsecs) distant from the Earth. This is an evolved giant star with a stellar classification of K4 III.[3]

Sigma Aurigae has a 12th magnitude companion at an angular separation of 8 arcseconds, as well as two fainter companions at 28 and 35" respectively.[10] All are background objects, stars much further away than Sigma itself.

Sigma Aurigae, along with λ Aur and μ Aur, were Kazwini's Al Ḣibāʽ (ألحباع), the Tent.[11] According to the catalogue of stars in the Technical Memorandum 33-507 – A Reduced Star Catalog Containing 537 Named Stars, Al Ḣibāʽ were the title for three stars: λ Aur as Al Ḣibāʽ I, μ Aur as Al Ḣibāʽ II and σ Aur as Al Ḣibāʽ III.[12]

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