Upsilon Cygni

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Upsilon Cygni
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Cygnus
Right ascension 21h 17m 55.07506s[1]
Declination +34° 53′ 48.8289″[1]
Apparent magnitude (V) 4.43[2]
Spectral type B2 Vne[3]
U−B color index −0.82[2]
B−V color index −0.11[2]
Radial velocity (Rv) −1.93±0.59[4] km/s
Proper motion (μ) RA: +10.03[1] mas/yr
Dec.: +6.49[1] mas/yr
Parallax (π) 5.08 ± 0.55[1] mas
Distance approx. 640 ly
(approx. 200 pc)
Mass 9.25±0.52[5] M
Radius 4.7[6] R
Luminosity (bolometric) 7,305[5] L
Surface gravity (log g) 3.30±0.10[7] cgs
Temperature 22,000[5] K
Rotational velocity (v sin i) 230±24[4] km/s
Age 17.0±2.8[8] Myr
Other designations
υ Cyg, 66 Cygni, BD+34° 4371, FK5 1559, HD 202904, HIP 105138, HR 8146, SAO 71173.[9]

Upsilon Cygni (υ Cyg) is a star in the northern constellation of Cygnus. It is visible to the naked eye, having an apparent visual magnitude of 4.43.[2] Based upon an annual parallax shift of 5.08 mas,[1] it lies at a distance of roughly 640 light years from the Sun.

This is a B-type main sequence star with a stellar classification of B2 Vne.[3] The 'e' suffix indicates this is a Be star, which means it is a rapidly rotating star surrounded by an orbiting gaseous disk. It has a high projected rotational velocity of about 230 km/s,[4] which accounts for the nebulous appearance of its lines as indicated by the 'n' suffix. The emission region of its disk has a radius of 0.20±0.04 AU.[6] The star itself is being viewed generally "pole-on", as ascertained by the lack of absorption features from the disk.[10]

Upsilon Cygni holds 9.3[5] times the mass of the Sun and is 4.7[6] times the Sun's radius. The rapid rotation is giving the star an oblate shape with an equatorial bulge that is 18% wider than the polar radius.[7] It is radiating 7,305[5] times the solar luminosity from its outer atmosphere at an effective temperature of 22,000 K.[5]

The star shows variations in luminosity, including short term non-radial pulsations with periods of 2.95 and 2.6 per day, as well as random outbursts occurring up to every few years. The latter may be associated with mass-loss episodes. There is suspicion this is a spectroscopic binary, but no companion has been detected via speckle interferometry. Measured variations in radial velocity may be caused by a companion having an orbital period of about 11.4 years.[7]


  1. ^ a b c d e f van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752Freely accessible, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357. 
  2. ^ a b c d Nicolet, B. (1978), "Photoelectric photometric Catalogue of homogeneous measurements in the UBV System", Astronomy and Astrophysics Supplement Series, 34: 1–49, Bibcode:1978A&AS...34....1N. 
  3. ^ a b Murphy, R. E. (November 1969), "A spectroscopic investigation of visual binaries with B-type primaries.", Astronomical Journal, 74: 1082−1094, Bibcode:1969AJ.....74.1082M, doi:10.1086/110908. 
  4. ^ a b c Becker, Juliette C.; et al. (April 2015), "Extracting Radial Velocities of A- and B-type Stars from Echelle Spectrograph Calibration Spectra", The Astrophysical Journal Supplement Series, 217 (2): 13, arXiv:1503.03874Freely accessible, Bibcode:2015ApJS..217...29B, doi:10.1088/0067-0049/217/2/29, 29. 
  5. ^ a b c d e f Hohle, M. M.; et al. (April 2010), "Masses and luminosities of O- and B-type stars and red supergiants", Astronomische Nachrichten, 331 (4): 349, arXiv:1003.2335Freely accessible, Bibcode:2010AN....331..349H, doi:10.1002/asna.200911355. 
  6. ^ a b c Rivinius, Thomas; et al. (2013), "Classical Be stars. Rapidly rotating B stars with viscous Keplerian decretion disks", The Astronomy and Astrophysics Review, 21: 69, arXiv:1310.3962Freely accessible, Bibcode:2013A&ARv..21...69R, doi:10.1007/s00159-013-0069-0. 
  7. ^ a b c Neiner, C.; et al. (July 2005), "Rotation, pulsations and outbursts in the Be star υ Cygni (HD 202904)", Astronomy and Astrophysics, 437 (1): 257−272, Bibcode:2005A&A...437..257N, doi:10.1051/0004-6361:20041901. 
  8. ^ Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (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:1007.4883Freely accessible, Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x. 
  9. ^ "ups Cyg -- Be Star", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2017-02-21. 
  10. ^ Peters, G. J. (February 1979), "An analysis of the far-ultraviolet spectra of the pole-on Be stars Upsilon Cygni and MU Centauri", Astrophysical Journal Supplement Series, 39: 175−193, Bibcode:1979ApJS...39..175P, doi:10.1086/190570.