V1794 Cygni
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Cygnus
Right ascension 20h 53m 53.652s[1]
Declination +44° 23′ 11.08″[1]
Apparent magnitude (V) 7.23[2]
Characteristics
Evolutionary stage Hertzsprung gap[3]
Spectral type G7III-IVne[4]
B−V color index 0.785±0.015[5]
Variable type FK Com[6]
Astrometry
Radial velocity (Rv)−30.76±0.33[2] km/s
Proper motion (μ) RA: 26.451 mas/yr[1]
Dec.: −0.877 mas/yr[1]
Parallax (π)8.8912 ± 0.0147 mas[1]
Distance366.8 ± 0.6 ly
(112.5 ± 0.2 pc)
Absolute magnitude (MV)2.21[5]
Details
Mass1.65[7] M☉
Radius6.1[8] R☉
Luminosity12.9[7] L☉
Temperature5,180±92[7] K
Rotation3.32 d[8]
Rotational velocity (v sin i)84.3±4.5[2] km/s
Age2.014[9] Gyr
Other designations
V1794 Cyg, BD+43°3759, GC 29168, HD 199178, HIP 103144, SAO 50198[10]
Database references
SIMBADdata

V1794 Cygni is a single variable star in the northern constellation Cygnus. It has the identifier HD 199178 from the Henry Draper Catalogue; V1794 Cygni is its variable star designation. With an apparent visual magnitude of 7.24, it's too dim to be visible with the naked eye but can be seen with binoculars. V1794 is located at a distance of 367 light-years (113 pc) based on parallax measurements, but is drifting closer to the Sun with a radial velocity of −31 km/s.[2] It lies superimposed over a region of faint nebulosity to the west of the North American Nebula.[11]

A visual band light curve for V1794 Cygni, adapted from Strassmeier et al. (1999)[12]

Spectrographs of HD 199178 taken in 1926 showed unusually diffuse lines for a star of its type.[11] In 1981, a broad, variable emission of Hydrogen alpha was noted, and the star showed a photometric variability with a period a few days. It showed extreme rotational broadening of the absorption lines but no variation in radial velocity.[13] The existence of a class of single, cool, rapidly rotating giant stars such as FK Com and HD 199178 presented a puzzle for astronomers.[13] The star showed a variable polarization with a period of four days, suggesting chromospheric activity with an asymmetric distribution of star spots and faculae, modulated by rotation.[14][15] Photometric measurements established a rotation period of 3.337 days by 1983.[16]

V1794 Cygni was classified as a Herbig Ae/Be star in 1999[17] in a catalog of UX Orionis stars. However, this proved incorrect because of the star's its fast rotation compared to other giants[18] and it is now classified as a FK Comae Berenices variable.[6] The stellar classification of V1794 Cygni is G7III-IVne,[4] matching an evolved subgiant/giant star with emission lines (e) plus "nebulous" lines (n) due to rapid rotation. It is currently crossing the Hertzsprung gap,[3] which indicates it has ceased core hydrogen burning.

This star has 165% of the mass and 6.1 times the radius of the Sun, but, with an age of around 2 billion years is younger than the latter. It is spinning with a projected rotational velocity of 84 km/s. V1794 Cygni is radiating 13 times the luminosity of the Sun from its enlarged photosphere at an effective temperature of 5,180 K,[7] which gives it a yellow hue. For a giant star it has an exceptionally high X-ray emission, which suggests there is a high surface density of active regions.[3]

References

  1. ^ a b c d Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
  2. ^ a b c d Frasca, A.; et al. (May 1, 2018). "A spectroscopic survey of the youngest field stars in the solar neighborhood . II. The optically faint sample". Astronomy and Astrophysics. 612: A96. arXiv:1801.00671. Bibcode:2018A&A...612A..96F. doi:10.1051/0004-6361/201732028. ISSN 0004-6361. S2CID 119537437.
  3. ^ a b c Gondoin, P. (January 2004). "The corona of HD 199178 (V 1794 Cygni)". Astronomy and Astrophysics. 413 (3): 1095–1104. Bibcode:2004A&A...413.1095G. doi:10.1051/0004-6361:20031575.
  4. ^ a b Huenemoerder, D. P. (September 1986). "Optical spectroscopy of HD 199178 : velocity and activity". Astronomical Journal. 92: 673–677. Bibcode:1986AJ.....92..673H. doi:10.1086/114201.
  5. ^ a b Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. S2CID 119257644.
  6. ^ a b Samus, N. N.; et al. (2017). "General Catalogue of Variable Stars". Astronomy Reports. 5.1. 61 (1): 80–88. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085. S2CID 255195566.
  7. ^ a b c d Luck, R. Earle (2015). "Abundances in the Local Region. I. G and K Giants". Astronomical Journal. 150 (3). 88. arXiv:1507.01466. Bibcode:2015AJ....150...88L. doi:10.1088/0004-6256/150/3/88. S2CID 118505114.
  8. ^ a b Strassmeier, Klaus G. (September 2009). "Starspots". The Astronomy and Astrophysics Review. 17 (3): 251–308. Bibcode:2009A&ARv..17..251S. doi:10.1007/s00159-009-0020-6.
  9. ^ Feltzing, S.; et al. (2001-10-01). "The solar neighbourhood age-metallicity relation - Does it exist?". Astronomy and Astrophysics. 377 (3): 911–924. arXiv:astro-ph/0108191. Bibcode:2001A&A...377..911F. doi:10.1051/0004-6361:20011119. ISSN 0004-6361. S2CID 4811000.
  10. ^ "HD 199178", SIMBAD, Centre de données astronomiques de Strasbourg, retrieved 2022-02-04.
  11. ^ a b Duncan, J. C. (March 1926). "Photographic studies of nebulae. IV". Astrophysical Journal. 63: 122–126. Bibcode:1926ApJ....63..122D. doi:10.1086/142956.
  12. ^ Strassmeier, K. G.; et al. (November 1999). "Starspot photometry with robotic telescopes. U BV (RI)C and by light curves of 47 active stars in 1996/97". Astronomy and Astrophysics Supplement Series. 140: 29–53. Bibcode:1999A&AS..140...29S. doi:10.1051/aas:1999116.
  13. ^ a b Bopp, B. W.; Stencel, R. E. (August 1981). "The FK COM stars". Astrophysical Journal. 247: L131–L134. Bibcode:1981ApJ...247L.131B. doi:10.1086/183606.
  14. ^ Piirola, V.; Vilhu, O. (June 1982). "Polarimetric observations of HD 199178- an FK COM type star". Astronomy and Astrophysics. 110: 351–354. Bibcode:1982A&A...110..351P.
  15. ^ Huovelin, J.; et al. (April 1987). "Five-colour (UBVRI) photopolarimetry of FK Comae and HD 199178". Astronomy and Astrophysics. 176: 83–92. Bibcode:1987A&A...176...83H.
  16. ^ Bopp, B. W.; et al. (December 1983). "Observations of active chromosphere stars". Astrophysical Journal. 275: 691–703. Bibcode:1983ApJ...275..691B. doi:10.1086/161566.
  17. ^ Herbst, W.; Shevchenko, V. S. (1999-08-01). "A Photometric Catalog of Herbig AE/BE Stars and Discussion of the Nature and Cause of the Variations of UX Orionis Stars". The Astronomical Journal. 118 (2): 1043–1060. Bibcode:1999AJ....118.1043H. doi:10.1086/300966. ISSN 0004-6256. S2CID 118185834.
  18. ^ "V1794 Cyg". The International Variable Star Index. AAVSO. Retrieved 29 December 2021.

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