{{short description|Star in the constellation of Coma Berenices}} {{Starbox begin | name = FK Comae Berenices }} {{Starbox image | image = [[Image:FKComLightCurve.png|250px]] | caption = [[Light curve]]s for FK Comae Berenices. The main plot shows the short term variability plotted from [[Transiting Exoplanet Survey Satellite|''TESS'']] data;<ref name=MAST/> the inset, adapted from Panov and Dimitrov (2007),<ref name="Panov"/> shows the long term variability. }} {{Starbox observe | epoch = J2000 | ra = {{RA|13|30|46.79937}}<ref name=GaiaDR2/> | dec = {{DEC|+24|13|57.7862}}<ref name=GaiaDR2/> | appmag_v = 8.14 – 8.33<ref name=gcvs/> | constell = [[Coma Berenices]] }} {{Starbox character | type = [[red giant branch]]<ref name=gondoin2002/> | class = G4 III<ref name=Strassmeier2009/> | b-v = | u-b = | variable = [[Variable star#FK Comae Berenices variables|FK Com]]<ref name=gcvs/> }} {{Starbox astrometry | radial_v = {{Val|−21.0|5.8}}<ref name=Strassmeier2009/> | prop_mo_ra = −51.969<ref name=GaiaDR2/> | prop_mo_dec = −22.262<ref name=GaiaDR2/> | parallax = 4.6102 | p_error = 0.0446 | parallax_footnote = <ref name=GaiaDR2/> | absmag_v = 1.2<ref name=korhonen1999/> }} {{Starbox detail | mass = 1.1<ref name=starhorse/> | radius = 6.99<ref name=GaiaDR2/> | luminosity = 26.8<ref name=GaiaDR2/> | temperature = 4,966<ref name=GaiaDR2/> | gravity = 2.359<ref name=mcdonald2017/> | metal_fe = −0.89<ref name=starhorse/> | rotation = 2.4 days<ref name=hackman2013/> | rotational_velocity = 160<ref name=Ayres2016/> | age_myr = }} {{Starbox catalog | names = {{odlist | BD=+24°2592 | FK5= | HD=117555 | HIP=65915 | HR= | SAO=82867 }}<ref name=SIMBAD/> }} {{Starbox reference | Simbad = FK+Comae+Berenices }} {{Starbox end}}
'''FK Comae Berenices''' is a [[variable star]] that varies in [[apparent magnitude]] between 8.14 and 8.33 over a period of 2.4 days. In 1966, Pavel Fedorovich Chugainov discovered that the star, then called HD 117555, varied in brightness.<ref name="Chugainov1966"/> It was given its [[variable star designation]], FK Comae Berenices, in 1968.<ref name="Kukarkin1968"/> It is the prototype for the [[Variable star#FK Comae Berenices variables|FK Comae Berenices]] (FK Com) class of variable stars. The variability of FK Com stars may be caused by large, cool spots on the rotating surfaces of the stars. This star is thought to be the result of a recent binary merger, resulting in a high rate of both spin and [[magnetic activity]].
The spectral class of FK Comae Berenices is G4 III, although it is considered unusual in having very broad [[absorption line]]s as well as some [[emission line]]s. The broadened spectral lines are due to rapid rotation.<ref name=Ayres2016/>
The rotation rate of FK Comae Berenices is unusually fast for a cool [[giant star]]. It is speculated that this is due to the merger of a contact binary pair of stars into a single star. The rotation produces extremely strong magnetic fields which are expected to [[Magnetic braking (astronomy)|brake]] the star to a slower rotation rate. Analysis of variability due to star spots on the surface show that the star rotates at different speeds at different latitudes.<ref name=hackman2013/>
FK Comae Berenices is listed as a companion to the slightly brighter HD 117567. The two are not thought to be physically associated, with HD 117567 being a much closer F2 [[main sequence]] star.<ref name=wds/>
==References== <references> <ref name=SIMBAD>{{cite simbad | title=FK Com | access-date=2019-01-06 }}</ref>
<ref name=GaiaDR2>{{Cite Gaia DR2|3937690377058804480}}</ref>
<ref name=gondoin2002>{{cite journal |last1=Gondoin |first1=P. |last2=Erd |first2=C. |last3=Lumb |first3=D. |title=Structure and evolution of FK Comae corona |journal=Astronomy and Astrophysics |date=2002 |volume=383 |issue=3 |page=919 |doi=10.1051/0004-6361:20011810 |bibcode=2002A&A...383..919G }}</ref>
<ref name=Ayres2016>{{citation | title=FK Comae Berenices, King of Spin: The COCOA-PUFS Project | last1=Ayres | first1=Thomas R. | last2=Kashyap | first2=V. | last3=Saar | first3=S. | last4=Huenemoerder | first4=D. | last5=Korhonen | first5=H. | last6=Drake | first6=J. J. | last7=Testa | first7=P. | last8=Cohen | first8=O. | last9=Garraffo | first9=C. | last10=Granzer | first10=T. | last11=Strassmeier | first11=K. | display-authors=1 | journal=[[The Astrophysical Journal Supplement Series]] | volume=223 | issue=1 | id=5 | pages=30 | date=March 2016 | doi=10.3847/0067-0049/223/1/5 | postscript=. | bibcode=2016ApJS..223....5A | arxiv=1601.03305 | s2cid=118501523 | doi-access=free }}</ref>
<ref name="Chugainov1966">{{cite journal | last1=Chugainov | first1=P. F. | title=New Microvariable HD 117555 | journal=Information Bulletin on Variable Stars | date=December 1966 | volume=172 | pages=1–2 | bibcode=1966IBVS..172....1C | url=https://ibvs.konkoly.hu/pub/ibvs/0101/0172.pdf | access-date=28 January 2025}}</ref>
<ref name="Kukarkin1968">{{cite journal | last1=Kukarkin | first1=B. V. | last2=Efremov | first2=Yu. N. | last3=Frolov | first3=M. S. | last4=Medvedeva | first4=G. I. | last5=Kholopov | first5=P. N. | last6=Kurochkin | first6=N. E. | last7=Kukarkina | first7=N. P. | last8=Perova | first8=N. B. | last9=Fedorovich | first9=V. P. | title=Identification List of the New Variable Stars Nominated in 1968 | journal=Information Bulletin on Variable Stars | date=November 1968 | volume=311 | bibcode=1968IBVS..311....1K | url=https://ibvs.konkoly.hu/pub/ibvs/0301/0311.pdf | access-date=28 January 2025}}</ref>
<ref name=Strassmeier2009>{{citation | title=Starspots | last1=Strassmeier | first1=Klaus G. | journal=[[The Astronomy and Astrophysics Review]] | volume=17 | issue=3 | pages=251–308 | date=September 2009 | doi=10.1007/s00159-009-0020-6 | bibcode=2009A&ARv..17..251S | postscript=. | doi-access=free }}</ref>
<ref name=korhonen1999>{{citation|title=Study of FK Comae Berenices. I. Surface images for 1994 and 1995|author1=Korhonen, H. |author2=Berdyugina, S. V. |author3=Hackman, T. |author4=Duemmler, R. |author5=Ilyin, I. V. |author6=Tuominen, I. |journal=[[Astronomy and Astrophysics]]|volume=346|page=103|date=1999|bibcode = 1999A&A...346..101K|postscript=.}}</ref>
<ref name=gcvs>{{citation|bibcode=2009yCat....102025S|title=VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007–2013)|journal=VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S|volume=1|pages=B/GCVS|display-authors=etal|last1=Samus|first1=N. N.|last2=Durlevich|first2=O. V.|year=2009|postscript=.}}</ref>
<ref name=MAST>{{cite web |title=MAST: Barbara A. Mikulski Archive for Space Telescopes |url=https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html |publisher=Space Telescope Science Institute |access-date=8 December 2021}}</ref>
<ref name=hackman2013>{{citation |doi=10.1051/0004-6361/201220690 |title=Flip-flops of FK Comae Berenices |year=2013 |last1=Hackman |first1=T. |last2=Pelt |first2=J. |last3=Mantere |first3=M. J. |last4=Jetsu |first4=L. |last5=Korhonen |first5=H. |last6=Granzer |first6=T. |last7=Kajatkari |first7=P. |last8=Lehtinen |first8=J. |last9=Strassmeier |first9=K. G. |journal=Astronomy & Astrophysics |volume=553 |pages=A40 |arxiv=1211.0914 |bibcode=2013A&A...553A..40H |s2cid=118705220 |postscript=. |doi-access=free }}</ref>
<ref name=wds>{{citation | bibcode=2001AJ....122.3466M | doi=10.1086/323920 | title=The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog | journal=The Astronomical Journal | volume=122 | issue=6 | pages=3466 | year=2001 | last1=Mason | first1=Brian D. | last2=Wycoff | first2=Gary L. | last3=Hartkopf | first3=William I. | last4=Douglass | first4=Geoffrey G. | last5=Worley | first5=Charles E. | doi-access=free |postscript=. }}</ref>
<ref name="Panov">{{cite journal |last1=Panov |first1=K. |last2=Dimitrov |first2=D. |title=Long-term photometric study of FK Comae Berenices and HD 199178 |journal=Astronomy and Astrophysics |date=May 2007 |volume=467 |pages=229–235 |doi=10.1051/0004-6361:20065596 |doi-access=free }}</ref>
<ref name=mcdonald2017>{{citation | postscript=. | title=Fundamental parameters and infrared excesses of Tycho–Gaia stars | year=2017 | last1=McDonald | first1=I. | last2=Zijlstra | first2=A. A. | last3=Watson | first3=R. A. | journal=Monthly Notices of the Royal Astronomical Society | volume=471 | issue=1 | pages=770–791 | bibcode=2017MNRAS.471..770M | arxiv=1706.02208 | doi=10.1093/mnras/stx1433 | doi-access=free }}</ref>
<ref name=starhorse>{{citation |bibcode=2019A&A...628A..94A |title=Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia DR2 stars brighter than G = 18 |last1=Anders |first1=F. |last2=Khalatyan |first2=A. |last3=Chiappini |first3=C. |last4=Queiroz |first4=A. B. |last5=Santiago |first5=B. X. |last6=Jordi |first6=C. |last7=Girardi |first7=L. |last8=Brown |first8=A. G. A. |last9=Matijevič |first9=G. |last10=Monari |first10=G. |last11=Cantat-Gaudin |first11=T. |last12=Weiler |first12=M. |last13=Khan |first13=S. |last14=Miglio |first14=A. |last15=Carrillo |first15=I. |last16=Romero-Gómez |first16=M. |last17=Minchev |first17=I. |last18=De Jong |first18=R. S. |last19=Antoja |first19=T. |last20=Ramos |first20=P. |last21=Steinmetz |first21=M. |last22=Enke |first22=H. |journal=Astronomy and Astrophysics |volume=628 |pages=A94 |year=2019 |arxiv=1904.11302 |doi=10.1051/0004-6361/201935765 |s2cid = 131780028 |postscript=.}}</ref> </references>
==External links== * [http://jumk.de/astronomie/special-stars/fk-comae-berenices.shtml FK Coma Berenices]
{{Stars of Coma Berenices}}
[[Category:Coma Berenices]] [[Category:Henry Draper Catalogue objects|117555]] [[Category:Objects with variable star designations|Comae Berenices, FK]] [[Category:G-type bright giants]] [[Category:FK Comae Berenices variables]] [[Category:Hipparcos objects|065915]] [[Category:Durchmusterung objects]]