Sigma Cygni

Sigma Cygni, Latinised from σ Cygni, is a blue supergiant star in the constellation Cygnus. Its apparent magnitude is 4.2. It belongs to the Cygnus OB4 stellar association and is located approximately 3,300 light years away from Earth.

σ Cygni

Location of σ Cygni (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Cygnus
Right ascension	21h 17m 24.95244s[1]
Declination	+39° 23′ 40.8528″[1]
Apparent magnitude (V)	4.233[2]
Characteristics
Spectral type	B9 Iab[2]
U−B color index	−0.386[2]
B−V color index	+0.123[2]
Astrometry
Radial velocity (Rv)	−5.30 ± 0.40[3] km/s
Proper motion (μ)	RA: −0.13[1] mas/yr Dec.: −3.58[1] mas/yr
Parallax (π)	1.13±0.19 mas[1]
Distance	1,000[4] pc
Absolute magnitude (MV)	−6.18[4]
Details
Mass	15[5] M☉
Radius	69.61[6][a] R☉
Luminosity	52,500[6] L☉
Surface gravity (log g)	1.85[2] cgs
Temperature	10,471[6] K
Metallicity	0.0[6]
Rotational velocity (v sin i)	14[2] km/s
Age	16[6] Myr
Other designations
67 Cyg, HD 202850, HR 8143, HIP 105102, 2MASS J21172494+3923402
Database references
SIMBAD	data

Because of its location in the galactic disk, σ Cyg is obstructed by interstellar dust and is reddened by around 0.2 magnitudes and loses about 0.6 magnitudes at visual wavelengths.^[2] Allowing for this, the star is over 50,000 times as luminous as the sun.

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 be the result of stellar oscillations.^[7] No clear variation in the brightness has been detected.^[8]

The elemental composition of Sigma Cygni is unusual. The star is enriched in helium, and has extremely high concentrations of nitrogen, calcium, cerium and europium, while carbon and aluminum are depleted relative to the Sun.^[6]

Notes

1. Applying the Stefan–Boltzmann law with a nominal solar effective temperature of 5,772 K:

   ${\displaystyle {\sqrt {{\biggl (}{\frac {5,772}{10,471}}{\biggr )}^{4}\cdot 10^{4.72}}}=69.61\ R_{\odot }}$.