}}{{Starbox reference
| Simbad=28+Cyg
}}{{Starbox end}}28 Cygni is a single[21][22] 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.[3] The distance to 28 Cyg, as estimated from its annual parallax shift of {{Val|5.3|ul=mas}},[1] is around 620 light years. It has an absolute magnitude of −2.56,[3] which means that if the star were just {{Convert|10|pc|ly|abbr=off}} away it would be brighter than Sirius, the brightest star in the night sky.
This is a B-type main-sequence star with a stellar classification of B2.5 V, per Lesh (1968).[4] Slettebak (1982) found a class of B2 IV(e),[5] 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,[14] and is classified as an SX Arietis variable by Samus et al. (2017).[7] 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.[14]
References
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2. ^1 2 {{citation | last1=Samus | first1=N. N. | last2=Kazarovets | first2=E. V. | last3=Durlevich | first3=O. V. | last4=Kireeva | first4=N. N. | last5=Pastukhova | first5=E. N. | display-authors=1 | title=General Catalogue of Variable Stars | version=5.1 | journal=Astronomy Reports | year=2017 | volume=61 | issue=1 | pages=80–88 | bibcode=2017ARep...61...80S | postscript=. }}
3. ^1 2 3 4 5 {{citation | title=XHIP: An extended hipparcos compilation | last1=Anderson | first1=E. | last2=Francis | first2=Ch. | journal=Astronomy Letters | volume=38 | issue=5 | pages=331 | year=2012 | bibcode=2012AstL...38..331A | doi=10.1134/S1063773712050015 | arxiv=1108.4971 | postscript=. }}
4. ^1 {{citation | title=Effects of gravitational darkening on the determination of fundamental parameters in fast-rotating B-type stars | last1=Frémat | first1=Y | last2=Zorec | first2=J | last3=Hubert | first3=A.-M | last4=Floquet | first4=M | display-authors=1 | journal=Astronomy and Astrophysics | volume=440|pages=305 | year=2005 | bibcode=2005A&A...440..305F | arxiv=astro-ph/0503381 | doi=10.1051/0004-6361:20042229 | postscript=. }}
5. ^1 2 {{citation | last1=Tetzlaff | first1=N. | last2=Neuhäuser | first2=R. | last3=Hohle | first3=M. M. | display-authors=1 | title=A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun | journal=Monthly Notices of the Royal Astronomical Society | volume=410 | issue=1 | pages=190–200 | date=January 2011 | doi=10.1111/j.1365-2966.2010.17434.x | bibcode=2011MNRAS.410..190T | postscript=. | arxiv=1007.4883 }}
6. ^1 2 {{citation | display-authors=1 | last1=McDonald | first1=I. | last2=Zijlstra | first2=A. A. | last3=Boyer | first3=M. L. | title=Fundamental parameters and infrared excesses of Hipparcos stars | journal=Monthly Notices of the Royal Astronomical Society | volume=427 | pages=343 | year=2012 | doi=10.1111/j.1365-2966.2012.21873.x | bibcode=2012MNRAS.427..343M | arxiv=1208.2037 | postscript=. }}
7. ^1 {{citation | title=Extracting Radial Velocities of A- and B-type Stars from Echelle Spectrograph Calibration Spectra | last1=Becker | first1=Juliette C. | last2=Johnson | first2=John Asher | last3=Vanderburg | first3=Andrew | last4=Morton | first4=Timothy D. | journal=The Astrophysical Journal Supplement Series | volume=217 | issue=2 | id=29 | pages=13 | date=April 2015 | doi=10.1088/0067-0049/217/2/29 | bibcode=2015ApJS..217...29B | arxiv=1503.03874 | display-authors=1 | postscript=. }}
8. ^1 {{citation | title=Detection of Additional Be+sdO Systems from IUE Spectroscopy | last1=Wang | first1=Luqian | last2=Gies | first2=Douglas R. | last3=Peters | first3=Geraldine J. | display-authors=1 | journal=The Astrophysical Journal | volume=853 | issue=2 | id=156 | pages=10 | date=February 2018 | doi=10.3847/1538-4357/aaa4b8 | bibcode=2018ApJ...853..156W }}
9. ^1 2 {{citation | last=Lesh | first=Janet Rountree | postscript=. | title=The Kinematics of the Gould Belt: an Expanding Group? | journal=Astrophysical Journal Supplement | volume=17 | page=371 | date=December 1968 | doi=10.1086/190179 | bibcode=1968ApJS...17..371L }}
10. ^1 2 {{citation | last1=Slettebak | first1=A. | title=Spectral types and rotational velocities of the brighter Be stars and A-F type shell stars | journal=Astrophysical Journal Supplement Series | volume=50 | pages=55–83 | id=80 | year = 1982 | bibcode=1982ApJS...50...55S | doi=10.1086/190820 }}
11. ^1 {{citation | last1=Eggleton | first1=P. P. | last2=Tokovinin | first2=A. A. | title=A catalogue of multiplicity among bright stellar systems | journal=Monthly Notices of the Royal Astronomical Society | volume=389 | issue=2 | pages=869–879 | date=September 2008 | doi=10.1111/j.1365-2966.2008.13596.x | bibcode=2008MNRAS.389..869E | arxiv=0806.2878 | postscript=. }}
12. ^1 2 3 4 {{citation | title=Short-term variability and mass loss in Be stars. III. BRITE and SMEI satellite photometry of 28 Cygni | last1=Baade | first1=D. | last2=Pigulski | first2=A. | last3=Rivinius | first3=Th. | last4=Carciofi | first4=A. C. | last5=Panoglou | first5=D. | last6=Ghoreyshi | first6=M. R. | last7=Handler | first7=G. | last8=Kuschnig | first8=R. | last9=Moffat | first9=A. F. J. | last10=Pablo | first10=H. | last11=Popowicz | first11=A. | last12=Wade | first12=G. A. | last13=Weiss | first13=W. W. | last14=Zwintz | first14=K. | display-authors=1 | journal=Astronomy & Astrophysics | volume=610 | id=A70 | pages=17 | date=March 2018 | doi=10.1051/0004-6361/201731187 | postscript=. | bibcode=2018A&A...610A..70B | arxiv=1708.07360 }}