31 Cygni

This article is about ο1/2 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
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 192579
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, ο2 Cygni or V695 Cygni, is a ternary 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.

  1. ^ a b c d e Cite error: The named reference dr3a was invoked but never defined (see the help page).
  2. ^ a b Cite error: The named reference gcvs was invoked but never defined (see the help page).
  3. ^ a b c d e f g h i j k l m Cite error: The named reference dr3c was invoked but never defined (see the help page).
  4. ^ a b c d Cite error: The named reference hr was invoked but never defined (see the help page).
  5. ^ Cite error: The named reference weaver was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference Eaton2008 was invoked but never defined (see the help page).
  7. ^ a b Cite error: The named reference griffin was invoked but never defined (see the help page).
  8. ^ a b c d Cite error: The named reference bennet was invoked but never defined (see the help page).
  9. ^ a b c 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. ^ Cite error: The named reference eaton was invoked but never defined (see the help page).
  11. ^ Cite error: The named reference benedetto was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference tetzlaff was invoked but never defined (see the help page).
  13. ^ a b Cite error: The named reference crossref was invoked but never defined (see the help page).
  14. ^ Cite error: The named reference wds was invoked but never defined (see the help page).
  15. ^ Cite error: The named reference dr3b was invoked but never defined (see the help page).
  16. ^ Cite error: The named reference Stencel was invoked but never defined (see the help page).