Astronomy:31 Cygni

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Short description: Triple star system in the constellation Cygnus
31 Cygni
Location of 31 Cygni (circled)
Observation data
{{#ifeq:J2000|J2000.0 (ICRS)|Epoch J2000.0      Equinox J2000.0 (ICRS)| Epoch J2000      [[Astronomy:Equinox (celestial coordinates)|Equinox J2000}}
Constellation Cygnus
31 Cygni A
Right ascension  20h 13m 37.908s[1]
Declination +46° 44′ 28.76″[1]
Apparent magnitude (V) 3.73 to 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][1] mas/yr
Dec.: 3.390[1] mas/yr
Parallax (π)2.9167 ± 0.1327[1] mas
Distance1,120 ± 50 ly
(340 ± 20 pc)
HD 192579
Proper motion (μ) RA: 3.906[3] mas/yr
Dec.: 1.978 mas/yr
Parallax (π)2.9160 ± 0.0336[3] mas
Distance1,120 ± 10 ly
(343 ± 4 pc)
Orbit[7]
Primary31 Cygni Aa
Companion31 Cygni Ab
Period (P)10.301+0.030
−0.037 years
Eccentricity (e)0.203+0.007
−0.008
Inclination (i)101.007+28.772
−18.623°
Longitude of the node (Ω)307.271+9.802
−11.253°
Periastron epoch (T)1950.508+0.171
−0.129
Argument of periastron (ω)
(secondary)		198.619+2.771
−1.963°
Semi-amplitude (K1)
(primary)		13.94±0.04[8] km/s
Semi-amplitude (K2)
(secondary)		18.0[9] km/s
Details
K supergiant
Mass9.44+1.51
−1.39[7] M☉
Radius127[10] R☉
Luminosity2,512 to 2,559[10] L☉
Temperature4,043±170[10] K
B dwarf
Mass6.475[7][lower-alpha 1] M☉
Radius5.2±0.5[11] R☉
Temperature16,500+1,000
−2,000[12] K
Age39.8[13] 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[14], 31 Cyg, ADS 13554, WDS J20136+4644
31 Cygni A (HD 192577): V695 Cyg, BD+46°2882, HD 192577, HIP 99675, HR 7735, SAO 49337
HD 192579: BD+46°2883, HD 192579, 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 is a ternary star system in the constellation of Cygnus. Alternatively, it is known as ο1 Cygni, Omicron1 Cygni, ο2 Cygni or V695 Cygni. Based on parallax measurements, it is located at a distance of approximately 1,120 light years.

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.[14]

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.[15] The 13th-magnitude star is likely to be an unrelated background object.[16]

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)[17]

31 Cygni A is an Algol-type eclipsing binary and ranges between magnitudes 3.73 and 3.89 over a period of ten years.[8] 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.[9]

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.

Notes

  1. ↑ from primary mass and mass ratio

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940  Gaia DR3 record for this source at VizieR.
  2. ↑ 2.0 2.1 Samus, N. N. 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. ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940  Gaia DR3 record for this source at VizieR.
  4. ↑ 4.0 4.1 4.2 4.3 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. doi:10.1086/309425. Bibcode: 2000ApJ...541..298W. 
  6. ↑ Eaton, Joel A. et al. (2008). "Orbits and Pulsations of the Classical ζ Aurigae Binaries". The Astrophysical Journal 679 (2): 1490–1498. doi:10.1086/587452. Bibcode: 2008ApJ...679.1490E. 
  7. ↑ 7.0 7.1 7.2 Videla, Miguel et al. (April 2022). "Bayesian Inference in Single-line Spectroscopic Binaries with a Visual Orbit" (in en). The Astronomical Journal 163 (5): 220. doi:10.3847/1538-3881/ac5ab4. ISSN 1538-3881. Bibcode: 2022AJ....163..220V. 
  8. ↑ 8.0 8.1 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. 
  9. ↑ 9.0 9.1 Bennett, Philip et al. (2018). "An Accurate Mass of the 31 Cygni Red Supergiant". Cambridge Workshop on Cool Stars: 46. doi:10.5281/zenodo.1467958. Bibcode: 2018csss.confE..46B. 
  10. ↑ 10.0 10.1 10.2 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. doi:10.3847/1538-3881/ab1cbd. Bibcode: 2019AJ....158...20M. 
  11. ↑ Eaton, Joel A. (1993). "31 Cygni: The B star and the wind". Astronomical Journal 106: 2081. doi:10.1086/116787. Bibcode: 1993AJ....106.2081E. 
  12. ↑ 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. 
  13. ↑ 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. doi:10.1111/j.1365-2966.2010.17434.x. Bibcode: 2011MNRAS.410..190T. 
  14. ↑ 14.0 14.1 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. 
  15. ↑ Mason, B. D. et al. (2014). "The Washington Visual Double Star Catalog". The Astronomical Journal 122 (6): 3466–3471. doi:10.1086/323920. Bibcode: 2001AJ....122.3466M. 
  16. ↑ Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940  Gaia DR3 record for this source at VizieR.
  17. ↑ 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. doi:10.1086/162153. Bibcode: 1984ApJ...281..751S. https://ui.adsabs.harvard.edu/abs/1984ApJ...281..751S. Retrieved 21 December 2021. 



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