Sigma Cygni

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Sigma Cygni
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Cygnus
Right ascension 21h 17m 24.95244s [1]
Declination +39° 23′ 40.8528″ [1]
Apparent magnitude (V) 4,21
Spectral type B9Iab [1]
Other designations
67 Cyg, HD 202850, HR 8143
Database references

Sigma Cygni (σ Cyg) is a star in the constellation Cygnus. Its apparent magnitude is 4.21. It is a blue supergiant. It belongs to Cygnus OB4 association and is located approximantly 1 kpc away from Earth and has estimated absolute magnitude -6.1.[2]

Because of its location at the galactic disk, it is obstructed by interstellar dust. Because the degree of dimming caused by the interstellar isn't known, luminicity values are uncertain. Conservative estimates give luminocity 26,500 L and radius 43 R (about 0.2 AU). The star is estimated based on these estimatates that it is 15-20 million years old and that originally it was 10-12 solar masses, and thus probably is a supernova progenitor.[3]

Spectral analysis of the star showed that photospheric Si ii and He i lines display a simultaneous, periodic variability. The periodicity was calculated at 1.59 hours in all three lines and it might by reasult of stellar oscillations.[4]


  1. ^ a b c SIMBAD, Sigma Cygni (accessed 26 August 2012)
  2. ^ Humphreys, R.M. (December 1978). "Studies of luminous stars in nearby galaxies. I. Supergiants and O stars in the Milky Way.". Astrophysical Journal, Suppl. Ser 38: 325. doi:10.1086/190559. 
  3. ^ Jim Kaler (9/03/2010) Sigma and V1334 Cygni (accessed 21 May 2015)
  4. ^ M. Kraus, S. Tomić, M. E. Oksala and M. Smole (June 2012). "Detection of a 1.59 h period in the B supergiant star HD 202850". Astronomy and Astrophysics 542: L32. doi:10.1051/0004-6361/201219319.