W Cygni is a semi-regular variable star in the constellation Cygnus, located 570 light-years from Earth. It lies less than half a degree southeast of ρ Cygni. W Cygni is, at times, a naked-eye star but it was not given a Bayer or Flamsteed designation. It has been proposed as a binary star system with a hotter main sequence companion, but this has not been confirmed.[9]

W Cygni

Location of W Cygni (circled)
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Cygnus
Right ascension	21h 36m 02.49619s[1]
Declination	+44° 22′ 28.5292″[1]
Apparent magnitude (V)	5.10 - 6.83[2]
Characteristics
Spectral type	M4e-M6e(Tc:)III[3]
U−B color index	+1.24[4]
B−V color index	+1.59[4]
Variable type	SRb[5]
Astrometry
Radial velocity (Rv)	−12.87[6] km/s
Proper motion (μ)	RA: 65.17 ± 0.42[1] mas/yr Dec.: 1.74 ± 0.30[1] mas/yr
Parallax (π)	5.72 ± 0.38 mas[1]
Distance	570 ± 40 ly (170 ± 10 pc)
Absolute magnitude (MV)	−0.43[7]
Details
Mass	0.98[8] M☉
Radius	227[8] R☉
Luminosity	5,888[8] L☉
Temperature	3,373[8] K
Other designations
W Cyg, BD+44°3877, HD 205730, HIP 106642, HR 8262
Database references
SIMBAD	data

W Cygni was discovered to be variable by John Ellard Gore, and first published in 1885.[10] It has a maximum magnitude of 5.10 and a minimum magnitude 6.83. The star is catalogued as having a primary period of 131.7 days, but shows variations with a variety of periods around 131 days as well as 234 days.[11][10] It is believed to be pulsating in the first overtone.[8] There is some evidence of additional very slow and small variations in the light curve on a time scale of 3,000–5,000 days.[12]

This star is an aging red giant on the asymptotic giant branch (AGB). Its spectral type ranges between M4e and M6e, and it shows possible elevated levels of Technetium.[2] The masses of AGB stars are poorly known, but using the pulsation properties of W Cygni, it mass is calculated to be slightly less than the sun's.[8] It has expanded to 227 times the girth of the Sun and is radiating 5,888 times the Sun's luminosity from its swollen photosphere at an effective temperature of 3,373 K.[8]

References