W Cygni
Semi-regular variable star in the constellation Cygnus
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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.[10]
  | |
| 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 | |
| Evolutionary stage | AGB[3] |
| Spectral type | M4e-M6e(Tc:)III[4] |
| U−B color index | +1.24[5] |
| B−V color index | +1.59[5] |
| Variable type | SRb[6] |
| Astrometry | |
| Radial velocity (Rv) | −12.87[7] 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[8] |
| Details | |
| Mass | 0.98[9] M☉ |
| Radius | 227[9] R☉ |
| Luminosity | 5,888[9] L☉ |
| Temperature | 3,373[9] 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.[11] 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.[12][11] It is believed to be pulsating in the first overtone.[9] 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.[13]
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.[9] 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.[9]