31 Cygni
Location of 31 Cygni (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Cygnus
31 Cygni A
Right ascension 20h 13m 37.908s[1]
Declination +46° 44′ 28.76″[1]
Apparent magnitude (V) 3.73 - 3.89[2]
HD 192379
Right ascension 20h 13m 39.199s[3]
Declination +46° 42′ 42.70″[3]
Apparent magnitude (V) 6.99[4]
Characteristics
31 Cygni A
Spectral type K3Ib + B2IV-V[5]
Variable type Algol[2]
HD 192579
Evolutionary stage main sequence[4][3]
Spectral type B5V[4]
Astrometry
31 Cygni A
Radial velocity (Rv)−7.41±0.08[6] km/s
Proper motion (μ) RA: 1.744[1] mas/yr
Dec.: 3.390[1] mas/yr
Parallax (π)2.9167 ± 0.1327 mas[1]
Distance1,120 ± 50 ly
(340 ± 20 pc)
HD 192579
Proper motion (μ) RA: 3.906[3] mas/yr
Dec.: 1.978[3] mas/yr
Parallax (π)2.9160 ± 0.0336 mas[3]
Distance1,120 ± 10 ly
(343 ± 4 pc)
Orbit[7]
Primary31 Cygni Aa
Companion31 Cygni Ab
Period (P)3,784.3 d
Eccentricity (e)0.2084±0.0031
Periastron epoch (T)2,452,345±9
Argument of periastron (ω)
(secondary)		204.5±1.0°
Semi-amplitude (K1)
(primary)		13.94±0.04 km/s
Semi-amplitude (K2)
(secondary)		18.0[8] km/s
Details
K supergiant
Mass6.73[8] M☉
Radius127[9] R☉
Luminosity2,512 - 2,559[9] L☉
Temperature4,043±170[9] K
B dwarf
Mass5.22[8] M☉
Radius5.2±0.5[10] R☉
Temperature16,500+1,000
−2,000[11] K
Age39.8[12] Myr
HD 192579
Mass4.1[3] M☉
Radius3.3[3] R☉
Luminosity373[3] L☉
Surface gravity (log g)4.04[3] cgs
Temperature13,949[3] K
Metallicity [Fe/H]+0.68[3] dex
Other designations
ο1 Cyg, ο2 Cyg,[13] 31 Cyg, ADS 13554, WDS J20136+4644
31 Cygni A (HD 192577): V695 Cyg, HD 192577, BD+46°2882, HIP 99675, HR 7735, SAO 49337
HD 192579: HD 192579, BD+46°2883, HIP 99676, SAO 49338
Database references
SIMBADdata
HD 192579
31 Cygni is the close pair, with 30 Cygni towards top left. (north is to the left)

31 Cygni, also known as ο1 Cygni, Omicron1 Cygni, or V695 Cygni, is a triple star system about 750 light years away in the constellation Cygnus.

The Bayer 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 the Flamsteed designation 31 Cygni.[13]

31 Cygni consists of a visible pair of stars 109″ apart as of 2016, and the brighter of the two is also a spectroscopic binary. 31 Cygni A is also designated HD 192577 and HR 7735, while its 7th-magnitude visual companion is designated HD 192579. Some multiple star catalogues designate a 13th-magnitude star 36″ 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]

An ultraviolet band light curve for the 1982 eclipse of V695 Cygni, adapted from Stencel et al. (1984)[16]

31 Cygni A is an Algol-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.

32 Cygni is about a degree away to the north, also a detached eclipsing binary system. It comprises a large cool evolved star and a small hot main sequence or subgiant companion.

References

  1. 1 2 3 4 5 Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  2. 1 2 Samus, 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.
  3. 1 2 3 4 5 6 7 8 9 10 11 12 13 Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  4. 1 2 3 4 Hoffleit, 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.
  5. ↑ Weaver, Wm. Bruce (2000). "Spectral Classification of Unresolved Binary Stars with Artificial Neural Networks". The Astrophysical Journal. 541 (1): 298–305. Bibcode:2000ApJ...541..298W. doi:10.1086/309425.
  6. ↑ Eaton, Joel A.; et al. (2008). "Orbits and Pulsations of the Classical ζ Aurigae Binaries". The Astrophysical Journal. 679 (2): 1490–1498. arXiv:0802.2238. Bibcode:2008ApJ...679.1490E. doi:10.1086/587452. S2CID 2079219.
  7. 1 2 Griffin, R. F. (2008). "Spectroscopic binary orbits from photoelectric radial velocities - Paper 202: 31 and 32 Cygni". The Observatory. 128: 362. Bibcode:2008Obs...128..362G.
  8. 1 2 3 4 Bennett, Philip; Brown, Alexander; Ayres, Thomas R. (2018). "An Accurate Mass of the 31 Cygni Red Supergiant". Cambridge Workshop on Cool Stars: 46. Bibcode:2018csss.confE..46B. doi:10.5281/zenodo.1467958.
  9. 1 2 3 Messineo, M.; Brown, A. G. A. (2019). "A Catalog of Known Galactic K-M Stars of Class I Candidate Red Supergiants in Gaia DR2". The Astronomical Journal. 158 (1): 20. arXiv:1905.03744. Bibcode:2019AJ....158...20M. doi:10.3847/1538-3881/ab1cbd. S2CID 148571616.
  10. ↑ Eaton, Joel A. (1993). "31 Cygni: The B star and the wind". Astronomical Journal. 106: 2081. Bibcode:1993AJ....106.2081E. doi:10.1086/116787.
  11. ↑ 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.
  12. ↑ Tetzlaff, N.; et al. (January 2011). "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun". Monthly Notices of the Royal Astronomical Society. 410 (1): 190–200. arXiv:1007.4883. Bibcode:2011MNRAS.410..190T. doi:10.1111/j.1365-2966.2010.17434.x. S2CID 118629873.
  13. 1 2 Kostjuk, 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.
  14. ↑ Mason, B. D.; et al. (2014). "The Washington Visual Double Star Catalog". The Astronomical Journal. 122 (6): 3466–3471. Bibcode:2001AJ....122.3466M. doi:10.1086/323920.
  15. ↑ Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  16. ↑ Stencel, Robert E.; Hopkins, Jeffrey L.; Hagen, Wendy; Fried, Robert; Schmidtke, Paul C.; Kondo, Yoji; Chapman, Robert D. (June 1984). "The 1982 eclipse of 31 Cygni". The Astrophysical Journal. 281: 751–759. Bibcode:1984ApJ...281..751S. doi:10.1086/162153. Retrieved 21 December 2021.
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