Upsilon Cygni

Upsilon Cygni, Latinized from υ Cygni, 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.

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]
Characteristics
Spectral type B2 Vne[3]
U−B color index −0.82[2]
B−V color index −0.11[2]
Astrometry
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
Distanceapprox. 640 ly
(approx. 200 pc)
Absolute magnitude (MV)−2.03[5]
Details
Mass9.25±0.52[6] M☉
Radius4.7[7] R☉
Luminosity (bolometric)7,305[6] L☉
Surface gravity (log g)3.30±0.10[8] cgs
Temperature22,000[6] K
Metallicity [Fe/H]−0.36[5] dex
Rotational velocity (v sin i)230±24[4] km/s
Age17.0±2.8[9] Myr
Other designations
υ Cyg, 66 Cygni, BD+34° 4371, FK5 1559, HD 202904, HIP 105138, HR 8146, SAO 71173.[10]
Database references
SIMBADdata

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.[7] The star itself is being viewed generally "pole-on", as ascertained by the lack of absorption features from the disk.[11]

Upsilon Cygni holds 9.3[6] times the mass of the Sun and is 4.7[7] 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.[8] It is radiating 7,305[6] times the solar luminosity from its outer atmosphere at an effective temperature of 22,000 K.[6]

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.[8]

References
  1. van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357.
  2. 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. 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. 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:1503.03874, Bibcode:2015ApJS..217...29B, doi:10.1088/0067-0049/217/2/29, 29.
  5. 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.
  6. 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:1003.2335, Bibcode:2010AN....331..349H, doi:10.1002/asna.200911355.
  7. 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:1310.3962, Bibcode:2013A&ARv..21...69R, doi:10.1007/s00159-013-0069-0.
  8. 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.
  9. 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:1007.4883, Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x.
  10. "ups Cyg -- Be Star", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2017-02-21.
  11. 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.
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