Its
apparent magnitude is 4.86, but this is slightly variable and the star is also called V1661 Cyg. When first analysed, it was classified as an irregular supergiant variable,[11] but subsequent studies have treated it as an
Alpha Cygni variable. It shows pulsations with multiple periods from a few hours to 22 days, and both
p- and g-modes.[6] Apart from p- and g-modes, strange mode and associated instabilities have also been found in models of this star.[12] The spectrum also shows variation, leading to different classifications being given for the star.[13]
The exact properties of 55 Cygni are not known precisely and are also variable. It is a hot luminous supergiant several hundred thousand times as luminous as the sun. This star was originally a standard for the B3 Ia spectral type.[14]
The type of pulsations that 55 Cyg exhibits suggest that it was previously a
red supergiant that has shed its outer layers. The most massive red supergiants are expected to pass through a blue supergiant phase before becoming a
Wolf-Rayet star and eventually exploding as a type Ib or Ic
supernova.[6]
^
abcDucati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237.
Bibcode:
2002yCat.2237....0D.
^
abSamus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1.
Bibcode:
2009yCat....102025S.
^Zorec, J.; Cidale, L.; Arias, M. L.; Frémat, Y.; Muratore, M. F.; Torres, A. F.; Martayan, C. (2009). "Fundamental parameters of B supergiants from the BCD system. I. Calibration of the (λ_1, D) parameters into Teff". Astronomy and Astrophysics. 501 (1): 297–320.
arXiv:0903.5134.
Bibcode:
2009A&A...501..297Z.
doi:
10.1051/0004-6361/200811147.
S2CID14969137.
^
abcdKraus, M.; Haucke, M.; Cidale, L. S.; Venero, R. O. J.; Nickeler, D. H.; Németh, P.; Niemczura, E.; Tomić, S.; Aret, A.; Kubát, J.; Kubátová, B.; Oksala, M. E.; Curé, M.; Kamiński, K.; Dimitrov, W.; Fagas, M.; Polińska, M. (2015). "Interplay between pulsations and mass loss in the blue supergiant 55 Cygnus = HD 198 478". Astronomy & Astrophysics. 581: A75.
arXiv:1507.01846.
Bibcode:
2015A&A...581A..75K.
doi:
10.1051/0004-6361/201425383.
S2CID55392478.
^Wilson, Ralph Elmer (1953). "General catalogue of stellar radial velocities". Washington.
Bibcode:
1953GCRV..C......0W.
^Morgan, W. W.; Roman, Nancy G. (1950). "Revised Standards for Supergiants on the System of the Yerkes Spectral Atlas". Astrophysical Journal. 112: 362.
Bibcode:
1950ApJ...112..362M.
doi:
10.1086/145351.