TheBayer designation ο (omicron) has been variously applied to two or three of the stars 30, 31, and 32 Cygni. 31 Cygni has been designated, variously, as ο1 or ο2 Cygni — therefore for clarity, it is preferred to use theFlamsteed designation 31 Cygni.[13]
31 Cygni consists of a visible pair of stars109″ apart as of 2016, and the brighter of the two is also aspectroscopic binary. 31 Cygni A is also designatedHD 192577 andHR 7735, while its 7th-magnitude visual companion is designatedHD 192579. Somemultiple star catalogues designate a 13th-magnitude star36″ from 31 Cygni A as 31 Cygni B, and HD 192579 as 31 Cygni C.[14] The 13th-magnitude star is likely to be an unrelated background object.[15]
The spectroscopic pair are an orange supergiant of spectral type K3Ib and a blue-white star likely to be evolving off the main sequence with a spectral type of B2IV-V. The visible companion is a 7th-magnitude B5 main sequence star.[4][3]
31 Cygni A is anAlgol-type eclipsing binary and ranges between magnitudes 3.73 and 3.89 over a period of ten years.[7] The eclipsing system has been studied in attempts to determine an accurate direct mass for a red supergiant. The value 6.73 M☉ is believed to be accurate to about 2%, but there are some discrepancies in the orbital fit.[8]
30 Cygni is another naked eye star a tenth of a degree away, forming a bright triple.
^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.
^abcdHoffleit, D.; Warren, W. H. (1995). "VizieR Online Data Catalog: Bright Star Catalogue, 5th Revised Ed. (Hoffleit+, 1991)".VizieR On-line Data Catalog: V/50. Originally Published in: 1964BS....C......0H.5050.Bibcode:1995yCat.5050....0H.
^abGriffin, R. F. (2008). "Spectroscopic binary orbits from photoelectric radial velocities - Paper 202: 31 and 32 Cygni".The Observatory.128: 362.Bibcode:2008Obs...128..362G.
^Di Benedetto, G. P.; Ferluga, S. (1990). "Angular diameters of Zeta Aurigae-type supergiants by Michelson interferometry".Astronomy and Astrophysics.236: 449.Bibcode:1990A&A...236..449D.
^abKostjuk, N. D. (2004). "VizieR Online Data Catalog: HD-DM-GC-HR-HIP-Bayer-Flamsteed Cross Index (Kostjuk, 2002)".VizieR On-line Data Catalog: IV/27A. Originally Published in: Institute of Astronomy of Russian Academy of Sciences (2002).4027.Bibcode:2004yCat.4027....0K.
