W_Cygni
W Cygni
Semi-regular variable star in the constellation Cygnus
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 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]