Sigma Aurigae
Star in the constellation Auriga
From Wikipedia, the free encyclopedia
Sigma Aurigae is a star in the northern constellation of Auriga. Its name is a Bayer designation that is Latinized from σ Aurigae, and abbreviated Sigma Aur or σ Aur. This star is faintly visible to the naked eye with an apparent visual magnitude of 4.99.[3] With an annual parallax shift of 6.35 mas,[2] it is approximately 530 light-years (160 parsecs) distant from the Earth. It is drifting closer to the Sun with a radial velocity of −20 km/s.[5]
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Auriga[1] |
| Right ascension | 05h 24m 39.141s[2] |
| Declination | +37° 23′ 07.26″[2] |
| Apparent magnitude (V) | 4.99[3] |
| Characteristics | |
| Evolutionary stage | red giant branch[2] |
| Spectral type | K3III CN+2[4] |
| U−B color index | +1.75[3] |
| B−V color index | +1.42[3] |
| Astrometry | |
| Radial velocity (Rv) | −19.7[5] km/s |
| Proper motion (μ) | RA: −0.564 mas/yr[2] Dec.: −10.953 mas/yr[2] |
| Parallax (π) | 6.3543±0.0892 mas[2] |
| Distance | 513 ± 7 ly (157 ± 2 pc) |
| Absolute magnitude (MV) | −0.75[1] |
| Details | |
| Radius | 43.72+1.08 −3.24[6] R☉ |
| Luminosity | 496±20[6] L☉ |
| Surface gravity (log g) | 1.75[7] cgs |
| Temperature | 4,120+162 −50[6] 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, GC 6636, HD 35186, HIP 25292, HR 1773, SAO 57981, PPM 70308, WDS J05247+3723A[9] | |
| Database references | |
| SIMBAD | data |
This is an evolved giant star with a stellar classification of K3III CN+2,[4] indicating that it has exhausted the supply of hydrogen at its core. The 'CN+2' notation indicates anomalously strong lines of the CN molecule in the spectrum. This star has expanded to 44 times the radius of the Sun and is radiating nearly 500[6] times the Sun's luminosity from its enlarged photosphere at an effective temperature of 4,120 K.[6] There is 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.[citation needed]
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]