View source for KY Cygni

{{short description|Star in the constellation Cygnus}}
{{Starbox begin
| name = KY&nbsp;Cygni
}}
{{Starbox image
 | image=
{{Location mark
|image=Sadr Region rgb.jpg|alt=|float=center|width=320
|label=|position=right
|mark=Red circle.svg|mark_width=10|mark_link=KY Cyg
|x=215|y=193
}}
|caption=Location of KY Cygni in the [[Sadr region]] (circled, east is up)
}}
{{Starbox observe
| epoch = [[J2000.0]]
| equinox = [[J2000.0]] ([[International Celestial Reference System|ICRS]])
| constell = [[Cygnus (constellation)|Cygnus]]
| ra = {{RA|20|25|58.04}}<ref name=dr3/>
| dec = {{DEC|+38|21|07.7}}<ref name=dr3/>
| appmag_v=11.14<ref name=mauron>{{cite journal|bibcode=2011A&A...526A.156M|title=The mass-loss rates of red supergiants and the de Jager prescription|journal=Astronomy and Astrophysics|volume=526|pages=A156|last1=Mauron|first1=N.|last2=Josselin|first2=E.|year=2011|doi=10.1051/0004-6361/201013993|arxiv = 1010.5369 |s2cid=119276502}}</ref> {{nowrap|(10.60 - 11.74<ref name=alfonso-garzon>{{cite journal |bibcode=2012A&A...548A..79A |title=The first INTEGRAL-OMC catalogue of optically variable sources |journal=Astronomy & Astrophysics |volume=548 |page=A79 |last1=Alfonso-Garzón |first1=J. |last2=Domingo |first2=A. |last3=Mas-Hesse |first3=J. M. |last4=Giménez |first4=A. |year=2012 |arxiv=1210.0821 |doi=10.1051/0004-6361/201220095|s2cid=118428054 }}</ref>)}}
}}
{{Starbox character
| class = M3 Ia<ref name=white/> (M3.5 Ia<ref name=gcvs1>KY Cyg, database entry, [http://www.sai.msu.su/groups/cluster/gcvs/gcvs/iii/iii.dat The combined table of GCVS Vols I-III and NL 67-78 with improved coordinates, General Catalogue of Variable Stars] {{Webarchive|url=https://web.archive.org/web/20170620004609/http://www.sai.msu.su/groups/cluster/gcvs/gcvs/iii/iii.dat |date=2017-06-20 }}, Sternberg Astronomical Institute, Moscow, Russia.  Accessed on line November 12, 2010.</ref>)
| b-v = +3.39<ref name=mauron/>
| u-b = +2.91<ref name=mauron/>
| variable = [[Slow irregular variable|Lc]]<ref name=gcvs1/>
}}
{{Starbox astrometry
| prop_mo_ra = −3.556<ref name=dr3/>
| prop_mo_dec = −6.061<ref name=dr3/>
| parallax = 0.6687
| p_error = 0.0517
| parallax_footnote = <ref name=dr3/>
| dist_pc = {{val|fmt=commas|1436|106|119}}
| dist_ly = {{val|{{convert|1436|pc|ly|disp=number}}|{{convert|106|pc|ly|disp=number}}|{{convert|119|pc|ly|disp=number}}|fmt=commas}}
| dist_footnote = <ref name="b-j"/>
| absmag_v = −8.18<ref name=levesque>{{cite journal|bibcode=2005ApJ...628..973L|title=The Effective Temperature Scale of Galactic Red Supergiants: Cool, but Not As Cool As We Thought|journal=The Astrophysical Journal|volume=628|issue=2|pages=973–985|author1-link=Emily Levesque|last1=Levesque|first1=Emily M.|last2=Massey|first2=Philip|last3=Olsen|first3=K. A. G.|last4=Plez|first4=Bertrand|last5=Josselin|first5=Eric|last6=Maeder|first6=Andre|last7=Meynet|first7=Georges|year=2005|doi=10.1086/430901|arxiv = astro-ph/0504337 |s2cid=15109583}}</ref>
}}
{{Starbox detail
| source = <ref name="Comeron"/>
| mass = 19
| radius = {{solar radius calculator|type=logLT|5.176|3535}}{{efn | name=radius | Applying the [[Stefan–Boltzmann law]] with a nominal [[sun|solar]] [[effective temperature]] of 5,772&nbsp;[[Kelvin|K]]: 
:<math>\sqrt{\biggl(\frac{5,772}{3,535}\biggr)^4 \cdot 10^{5.176}} = 1,032.46\ R_\odot</math>.}}
 | temperature=3,535
| luminosity = 150,000
| metal=
| gravity=−0.5<ref name=levesque/>
| rotation=
| age_myr=>9{{efn|This is only the age at which the star enters the red supergiant phase.}}
}}
{{Starbox catalog
| names=[[Variable star designation|KY]]&nbsp;Cyg, [[Guide Star Catalog|GSC]]&nbsp;03152-01140, [[IRAS]]&nbsp;20241+3811, IRC+40415, [[Tycho Catalogue|TYC]]&nbsp;3152-1140-1, [[RAFGL]]&nbsp;2575, [[USNO CCD Astrograph Catalog|UCAC2]]&nbsp;45230193, [[2MASS]]&nbsp;J20255805+3821076
}}
{{Starbox reference
| Simbad=KY+Cyg}}
{{Starbox end}}

'''KY Cygni''' is a [[variable star|variable]] [[red supergiant]] of [[spectral class]] M3Ia located in the [[constellation]] [[Cygnus (constellation)|Cygnus]]. It is approximately 4,700 [[light-years]] away.

==Observations==
KY Cyg lies near the bright [[open cluster]] [[NGC 6913]], but is not thought to be a member.  The location is close to the bright star [[Gamma Cygni|γ Cygni]].<ref name=romano>{{cite journal|bibcode=1969MmSAI..40..375R|title=Researches with the Schmidt telescopes. III. Variable stars in the field of gamma Cygni|journal=Memorie della Società Astronomia Italiana|volume=40|pages=375|last1=Romano|first1=G.|year=1969}}</ref> It was identified as a variable star in 1930,<ref>{{cite journal|bibcode=1930MiSon..17....1H|title=Relative Koordinaten, Oerter und Karten neuer Veraenderlicher|journal=Mitteilungen der Sternwarte zu Sonneberg|volume=17|pages=1|last1=Hoffmeister|first1=Cuno|year=1930}}</ref> and later named as KY Cygni.<ref>{{cite journal|bibcode=1941KVeBB...6....4A|title=Die Veraenderlichen Sterne der noerdlichen Milchstrasse. Teil II|journal=Kleine Veroeffentlichungen der Universitaetssternwarte zu Berlin Babelsberg|volume=6|pages=4.1|last1=Ahnert|first1=P.|last2=Van Schewick|first2=H.|last3=Hoffmeister|first3=C.|year=1941}}</ref>  The spectrum was given the MK classification of M3 Ia, with only minor adjustments since.<ref name=white>{{cite journal|bibcode=1978ApJ...222..209W|title=Photoelectric two-dimensional spectral classification of M supergiants|journal=Astrophysical Journal|volume=222|pages=209|last1=White|first1=N. M.|last2=Wing|first2=R. F.|year=1978|doi=10.1086/156136|doi-access=free}}</ref>

KY Cygni is heavily reddened due to [[interstellar extinction]], losing an estimated 7.75 magnitudes at visual wavelengths. It would be a naked eye star if no light was lost.<ref name=levesque/>

==Properties==
[[File:Mukyv354.png|thumb|left|upright=1.0|Size comparison of [[Betelgeuse]], [[Mu Cephei]], KY Cygni, and [[V354 Cephei]], according to estimates derived in 2005<ref name=levesque/>]]
KY Cygni is classified as a luminous red supergiant with a strong [[stellar wind]].  It is losing mass at around {{val|4.9|e=-6|u={{solar mass|link=y}}}} and has been described as a cool [[hypergiant]].<ref name=mauron/><ref name=stickland>{{cite journal|bibcode=1985Obs...105..229S|title=IRAS observations of the cool galactic hypergiants|journal=The Observatory|volume=105|pages=229|last1=Stickland|first1=D. J.|year=1985}}</ref>

Its properties are uncertain, but the temperature is around 3,500 K.  A model fit based on [[K band (infrared)|K-band]] infrared brightness gives a luminosity of {{solar luminosity|273,000}}, corresponding to a radius of {{solar radius|1,420}}.  Another model based on visual brightness gives an unexpectedly large luminosity of {{solar luminosity|1,107,000}}, with the difference due mainly to the assumptions about the level of extinction. The radius corresponding to the higher luminosity would be {{solar radius|2,850}}. These parameters are larger and more luminous than expected for any red supergiant, making them doubtful.<ref name=levesque/> More recently, integration of the [[spectral energy distribution]]s across a full range of wavelengths from [[UBV photometric system|U band]] to the 60 micron microwave flux gives an even lower luminosity of {{solar luminosity|138,000}},<ref name=mauron/> and a 2020 paper published a luminosity of {{solar luminosity|150,000}}, which give a smaller radius of {{solar radius calculator|type=logLT|5.176|3535|unit=y}} using an [[effective temperature]] of 3,535{{Nbsp}}K.<ref name="Comeron"/>

[[File:KYCygLightCurve.png|thumb|left|A [[Photometric_system#Photometric_letters|visual band]] [[light curve]] for KY Cygni, plotted from data published by Kochanek ''et al.'' (2017)<ref name="Kochanek"/>]]
KY Cygni is a variable star with a large amplitude but no clear periodicity. At times, it varies rapidly, at others it is fairly constant for long periods.<ref name=romano/>  The photographic magnitude range is given as 13.5 - 15.5,<ref name=gcvs1/> while a visual range is 10.60 - 11.74.<ref name=alfonso-garzon/>

{{clear left}}
== See also ==

* [[List of largest known stars]]

==Notes==
{{Notelist}}

==References==
{{reflist|refs=

<ref name=dr3>{{cite Gaia DR3|2058131491974019968}}</ref>

<ref name="b-j">{{Cite journal |last1=Bailer-Jones |first1=C. A. L. |last2=Rybizki |first2=J. |last3=Fouesneau |first3=M. |last4=Demleitner |first4=M. |last5=Andrae |first5=R. |date=2021-03-01 |title=Estimating distances from parallaxes. V: Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3 |journal=The Astronomical Journal |volume=161 |issue=3 |pages=147 |doi=10.3847/1538-3881/abd806 |doi-access=free |arxiv=2012.05220 |bibcode=2021AJ....161..147B |issn=0004-6256}} Data about this star can be seen [https://dc.zah.uni-heidelberg.de/gedr3dist/q/cone/form here].</ref>

<ref name="Comeron">{{Cite journal|last1=Comerón|first1=F.|last2=Djupvik|first2=A. A.|last3=Schneider|first3=N.|last4=Pasquali|first4=A.|date=October 2020|title=The historical record of massive star formation in Cygnus|journal=Astronomy & Astrophysics|volume=644|pages=A62|arxiv=2009.12779|bibcode=2020A&A...644A..62C|doi=10.1051/0004-6361/202039188|s2cid=221970180}}</ref>

<ref name="Kochanek">{{cite journal |last1=Kochanek |first1=C. S. |last2=Shappee |first2=B. J. |last3=Stanek |first3=K. Z. |last4=Holoien |first4=T. W. S. |last5=Thompson |first5=Todd A. |last6=Prieto |first6=J. L. |last7=Dong |first7=Subo |last8=Shields |first8=J. V. |last9=Will |first9=D. |last10=Britt |first10=C. |last11=Perzanowski |first11=D. |last12=Pojmański |first12=G. |title=The All-Sky Automated Survey for Supernovae (ASAS-SN) Light Curve Server v1.0 |journal=Publications of the Astronomical Society of the Pacific |date=October 2017 |volume=129 |issue=980 |page=104502 |doi=10.1088/1538-3873/aa80d9 |arxiv=1706.07060 |bibcode=2017PASP..129j4502K |doi-access=free }}</ref>

}}

==External links==
* http://jumk.de/astronomie/big-stars/ky-cygni.shtml
* http://www.astronomy.com/asy/default.aspx?c=a&id=2772
*[http://www.space.com/scienceastronomy/aas_largest_stars_050110.html List of Largest Stars Gets 3 New Chart Toppers], Robert Roy Britt, space.com, 10 January 2005.  Accessed on line November 12, 2010.

{{Stars of Cygnus}}

[[Category:M-type supergiants]]
[[Category:Cygnus (constellation)]]
[[Category:Slow irregular variables]]
[[Category:Objects with variable star designations|Cygni, KY]]
[[Category:2MASS objects|J20255805+3821076]]
[[Category:IRAS catalogue objects]]
[[Category:M-type hypergiants]]
[[Category:Population I stars]]