31 Cygni

31 Cygni, also known as ο1 Cygni, Omicron1 Cygni, or V695 Cygni, is a star in the constellation Cygnus.

This article is about ο1 Cygni. For other star systems with this Bayer designation, see ο Cygni.
31 Cygni
Location of 31 Cygni (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Cygnus
Right ascension  20h 13m 37.911s[1]
Declination +46° 44′ 28.739″[1]
Apparent magnitude (V) 3.73 - 3.89[2]
Characteristics
Spectral type K4Iab + B4IV-V[2]
Variable type Algol[2]
Astrometry
Radial velocity (Rv)–7.41 ± 0.08[3] km/s
Proper motion (μ) RA: 0.133 ± 0.672[1] mas/yr
Dec.: 4.834 ± 0.633[1] mas/yr
Parallax (π)4.3432 ± 0.3464[1] mas
Distance750 ± 60 ly
(230 ± 20 pc)
Orbit[4]
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[5] km/s
Details
K supergiant
Mass6.73[5] M☉
Radius127[6] R☉
Luminosity2,512 - 2,559[6] L☉
Temperature4,043±170[6] K
B dwarf
Mass5.22[5] M☉
Radius5.2 ± 0.5[7] R☉
Temperature16,500+1,000
−2,000[8] K
Age39.8[9] Myr
Other designations
ο1 Cyg, ο2 Cyg,[10] 31 Cyg, V695 Cyg, HD 192577, BD+46°2882, HIP 99675, HR 7735, SAO 49337
Database references
SIMBADdata
31 Cygni is the close pair. The third star is 30 Cygni.

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.[10]

It is an Algol-type eclipsing binary and ranges between magnitudes 3.73 and 3.89 over a period of ten years. The component stars are an orange supergiant of spectral type K4Iab and a blue-white star likely to be evolving off the main sequence with a spectral type of B4IV-V. 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.[5]

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. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  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. 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.
  4. 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.
  5. 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.
  6. 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: 20. arXiv:1905.03744. Bibcode:2019AJ....158...20M. doi:10.3847/1538-3881/ab1cbd.
  7. Eaton, Joel A. (1993). "31 Cygni: The B star and the wind". Astronomical Journal. 106: 2081. Bibcode:1993AJ....106.2081E. doi:10.1086/116787.
  8. 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.
  9. 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.
  10. 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.
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