28 Cygni

28 Cygni is a single[12][13] star in the northern constellation of Cygnus. It is a faint blue-white hued star but visible to the naked eye with an apparent visual magnitude of 4.93.[2] The distance to 28 Cyg, as estimated from its annual parallax shift of 5.3 mas,[1] is around 620 light years. It has an absolute magnitude of −2.56,[2] which means that if the star were just 10 parsecs (33 light-years) away it would be brighter than Sirius, the brightest star in the night sky.

This article is about b2 Cygni. For other stars with this Bayer designation, see b Cygni.
28 Cygni
Observation data
Epoch J2000      Equinox J2000
Constellation Cygnus
Right ascension  20h 09m 25.61909s[1]
Declination +36° 50′ 22.5961″[1]
Apparent magnitude (V) 4.93[2]
Characteristics
Spectral type B2.5 V[3] or B2 IV(e)[4]
B−V color index −0.139±0.004[2]
Variable type SX Ari[5]
Astrometry
Radial velocity (Rv)−0.36±2.59[6] km/s
Proper motion (μ) RA: +2.728[1] mas/yr
Dec.: +15.562[1] mas/yr
Parallax (π)5.2947 ± 0.2255[1] mas
Distance620 ± 30 ly
(189 ± 8 pc)
Absolute magnitude (MV)−2.56[2]
Details
Mass9.5±0.3[7] M☉
Radius5.7[8] R☉
Luminosity1,353.22[9] L☉
Surface gravity (log g)3.983[10] cgs
Temperature11,338[9] K
Rotational velocity (v sin i)320[8] km/s
Age22.1±2.8[7] Myr
Other designations
b2 Cygni, 28 Cygni, V1624 Cygni, BD+36°3907, HD 191610, HIP 99303, HR 7708, SAO 69518[11]
Database references
SIMBADdata

This is a B-type main-sequence star with a stellar classification of B2.5 V, per Lesh (1968).[3] Slettebak (1982) found a class of B2 IV(e),[4] which would suggest this is a more evolved subgiant star. It is a Be star, which means the spectrum displays emission lines due a disk of ejected gas in a Keplerian orbit around the star. The star displays short-term variability with two or more periods,[8] and is classified as an SX Arietis variable by Samus et al. (2017).[5] It is spinning rapidly with a projected rotational velocity of 320 km/s; estimated at round 80% of the critical rotation rate. This is giving the star an oblate shape with an equatorial bulge out to 6.5 times the Sun's radius, compared to 5.7 at the poles.[8]

References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. 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.
  3. Lesh, Janet Rountree (December 1968), "The Kinematics of the Gould Belt: an Expanding Group?", Astrophysical Journal Supplement, 17: 371, Bibcode:1968ApJS...17..371L, doi:10.1086/190179.
  4. Slettebak, A. (1982), "Spectral types and rotational velocities of the brighter Be stars and A-F type shell stars", Astrophysical Journal Supplement Series, 50: 55–83, Bibcode:1982ApJS...50...55S, doi:10.1086/190820, 80
  5. Samus, N. N.; et al. (2017), "General Catalogue of Variable Stars", Astronomy Reports, 5.1, 61 (1): 80–88, Bibcode:2017ARep...61...80S.
  6. 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.
  7. 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, arXiv:1007.4883, Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x.
  8. Baade, D.; et al. (March 2018), "Short-term variability and mass loss in Be stars. III. BRITE and SMEI satellite photometry of 28 Cygni", Astronomy & Astrophysics, 610: 17, arXiv:1708.07360, Bibcode:2018A&A...610A..70B, doi:10.1051/0004-6361/201731187, A70.
  9. McDonald, I.; et al. (2012), "Fundamental parameters and infrared excesses of Hipparcos stars", Monthly Notices of the Royal Astronomical Society, 427: 343, arXiv:1208.2037, Bibcode:2012MNRAS.427..343M, doi:10.1111/j.1365-2966.2012.21873.x.
  10. Frémat, Y; et al. (2005), "Effects of gravitational darkening on the determination of fundamental parameters in fast-rotating B-type stars", Astronomy and Astrophysics, 440: 305, arXiv:astro-ph/0503381, Bibcode:2005A&A...440..305F, doi:10.1051/0004-6361:20042229.
  11. "28 Cyg". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-01-11.
  12. Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x.
  13. Wang, Luqian; et al. (February 2018), "Detection of Additional Be+sdO Systems from IUE Spectroscopy", The Astrophysical Journal, 853 (2): 10, arXiv:1801.01066, Bibcode:2018ApJ...853..156W, doi:10.3847/1538-4357/aaa4b8, 156
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