{{short description|Star in the constellation Coma Berenices}} {{Starbox begin}} {{Starbox image | image = [[Image:UUComLightCurve.png|250px]] | caption = A [[Photometric_system#Photometric_letters|visual band]] [[light curve]] for UU Comae Berenices from [[MOST (spacecraft)|''MOST'']] data. Adapted from Paunzen ''et al.'' (2019)<ref name=Paunzen2019/> }} {{Starbox observe | epoch = J2000.0 | equinox = J2000.0 ([[International Celestial Reference System|ICRS]]) | constell = [[Coma Berenices (constellation)|Coma Berenices]] | ra = {{RA|12|31|00.561}}<ref name=GaiaDR3/> | dec = {{DEC|+24|34|01.80}}<ref name=GaiaDR3/> | appmag_v = 5.41 – 5.46<ref name=Samus2017/> }} {{Starbox character | type = main sequence<ref name=Paunzen2019/> | class = A3p SrCr<ref name=Renson2009/> | b-v = {{Val|0.056|0.008}}<ref name=Anderson2012/> | variable = [[Alpha2 Canum Venaticorum variable|α<sup>2</sup> CVn]]<ref name=Paunzen2019/> + [[Delta Scuti variable|δ Sct]]<ref name=Samus2017/> }} {{Starbox astrometry | radial_v = {{Val|+1.0|1.8}}<ref name=Anderson2012/> | prop_mo_ra = −12.474 | prop_mo_dec = −9.085 | pm_footnote = <ref name=GaiaDR3/> | parallax = 12.0785 | p_error = 0.1214 | parallax_footnote = <ref name=GaiaDR3/> | absmag_v = 0.66<ref name=Anderson2012/> }} {{Starbox detail | source = <ref name=Paunzen2019/> | mass = {{Val|2.29|0.10}} | radius = {{Val|2.6|0.2}} | metal_fe = | gravity = {{Val|3.9|0.2}} | age_myr = 400–800 | luminosity = {{Val|38.2|1.3}} | temperature = {{Val|8900|200|fmt=commas}} | rotational_velocity = {{Val|63|2}} | rotation = 2.05219 d }} {{Starbox catalog | names = {{odlist | name=Kissīn<ref name=Allen1963/> | V=UU Com | F=21 Com | BD=+25°2517 | HD=108945 | HIP=61071 | HR=4766 | SAO=82346 }}<ref name=Simbad/> }} {{Starbox reference | Simbad = 21+com }} {{Starbox end}}
'''21 Comae Berenices''' is a [[variable star]] in the northern [[constellation]] of [[Coma Berenices]].<ref name=":0" /> It has the [[variable star designation]] UU Comae Berenices, while 21 Comae Berenices is the [[Flamsteed designation]].<ref name=Simbad/><ref name=":0">{{Cite web |title=21 Comae Berenices - Star in Coma Berenices {{!}} TheSkyLive.com |url=https://theskylive.com/sky/stars/21-comae-berenices-star |access-date=2023-06-13 |website=theskylive.com}}</ref><ref>{{Cite web |last=Guide |first=Universe |date=25 January 2015 |title=21 Comae Berenices Star Facts |url=https://www.universeguide.com/star/61071/21comaeberenices |access-date=13 June 2023 |website=Universe Guide |language=en-US}}</ref>
== About == According to [[Richard Hinckley Allen|R. H. Allen]], English [[Oriental studies|orientalist]] [[Thomas Hyde]] attributed the ancient title Kissīn to this star, a name that comes from a climbing plant – either [[convolvulus|bindweed]] or [[dog rose]].<ref name="Allen1963" /> This star has a white hue and is just visible to the [[naked eye]] with an [[apparent visual magnitude]] that fluctuates at about 5.4.<ref name=Samus2017/> Based upon [[stellar parallax|parallax]] measurements, it is located at a distance of approximately 270 [[light year]]s away from the Sun.<ref name="GaiaDR3" /> It is a single star but is a confirmed physical member of the [[Coma Star Cluster|Melotte 111]] [[open cluster]].<ref name="Silaj2014" />
== History == This object has been studied extensively since 1953, producing some occasionally contradictory results such as hints of [[Pulsating variable|pulsational behavior]] or a [[spectroscopic binary|binary companion]]. It is a weakly magnetic [[chemically peculiar star|chemically peculiar]] star of type CP2, or [[Ap and Bp stars|Ap star]], that is most likely on the [[main sequence]].<ref name=Paunzen2019/> The [[stellar classification]] is A3p SrCr,<ref name=Renson2009/> where the suffix notation indicates abundance anomalies of the [[iron-peak element]] chromium, as well as strontium.
In 1950, [[Olin J. Eggen|Olin Jeuck Eggen]] reported that the brightness of 21 Comae Berenices is variable.<ref name="Eggen1950"/> This is an [[Alpha2 Canum Venaticorum variable|Alpha<sup>2</sup> Canum Venaticorum (ACV) variable]], which indicates it varies in luminosity as it rotates due to [[star spot|spots]] on its surface created by a [[stellar magnetic field|magnetic field]]. The range of variation has an [[amplitude]] of 0.02 magnitude and a period of just over two days.<ref name=Paunzen2019/> Samus et al. (2017) have it classified as a low-amplitude [[Delta Scuti variable]],<ref name=Samus2017/> although this is disputed.<ref name=Paunzen2019/>
The age of the Melotte 111 cluster, and therefore this star, lies in the range of 400–800 million years. The star has a [[projected rotational velocity]] of 63 km/s, with a polar inclination of 64° or greater, resulting in a rotation period of 2.05 days. Stellar evolutionary models yield a mass of around 2.3 times that of the Sun and 2.6 times the [[Sun's radius]] for this object. It is radiating 38 times the [[luminosity of the Sun]] from its [[photosphere]] at an [[effective temperature]] of 8,900 K.<ref name=Paunzen2019/>
==References== <references> <ref name=GaiaDR3>{{Cite Gaia DR3|3959965486205062528}}</ref>
<ref name=Simbad>{{cite simbad | title=21 Com | access-date=2019-11-01}}</ref>
<ref name=Samus2017>{{citation | title=General catalogue of variable stars: Version GCVS 5.1 | 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 | journal=Astronomy Reports | volume=61 | issue=1 | pages=80 | year=2017 | postscript=. | doi=10.1134/S1063772917010085 | bibcode=2017ARep...61...80S | s2cid=125853869 }}</ref>
<ref name="Eggen1950">{{cite journal | last1=Eggen | first1=Olin J. | title=Photoelectric Studies.IV. Color-Luminosity Array for Stars in the Region of the Sun | journal=Astrophysical Journal | date=July 1950 | volume=112 | pages=141-177 | bibcode=1950ApJ...112..141E | doi=10.1086/145324 | url=https://articles.adsabs.harvard.edu/pdf/1950ApJ...112..141E | access-date=8 February 2025}}</ref>
<ref name=Anderson2012>{{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 | arxiv=1108.4971 | doi=10.1134/S1063773712050015 | s2cid=119257644 }}</ref>
<ref name=Paunzen2019>{{citation | title=A revisit to the enigmatic variable star 21 Comae | display-authors=1 | last1=Paunzen | first1=Ernst | last2=Handler | first2=Gerald | last3=Walczak | first3=Przemysław | last4=Hümmerich | first4=Stefan | last5=Niemczura | first5=Ewa | last6=Kallinger | first6=Thomas | last7=Weiss | first7=Werner | last8=Bernhard | first8=Klaus | last9=Fedurco | first9=Miroslav | last10=Gütl-Wallner | first10=Anna | last11=Matthews | first11=Jaymie | last12=Pribulla | first12=Theodor | last13=VaÅko | first13=Martin | last14=Wallner | first14=Stefan | last15=RóŻański | first15=Tomasz | journal=Monthly Notices of the Royal Astronomical Society | volume=485 | issue=3 | pages=4247–4259 | date=May 2019 | doi=10.1093/mnras/stz413 | doi-access=free | arxiv=1904.04809 | bibcode=2019MNRAS.485.4247P | s2cid=104292433 | postscript=. }}</ref>
<ref name=Renson2009>{{citation | title=Catalogue of Ap, HgMn and Am stars | last1=Renson | first1=P. | last2=Manfroid | first2=J. | journal=Astronomy and Astrophysics | postscript=. | volume=498 | issue=3 | pages=961–966 | year=2009 | bibcode=2009A&A...498..961R | doi=10.1051/0004-6361/200810788 | doi-access=free }}</ref>
<ref name=Silaj2014>{{citation | last1=Silaj | first1=J. | last2=Landstreet | first2=J. D. | title=Accurate age determinations of several nearby open clusters containing magnetic Ap stars | journal=Astronomy & Astrophysics | volume=566 | pages=A132 | year=2014 | bibcode=2014A&A...566A.132S | arxiv=1407.4531 | doi=10.1051/0004-6361/201321468 | s2cid=53370832 | postscript=. }}</ref>
<ref name=Allen1963>{{citation | first=Richard Hinckley | last=Allen | year=1963 | publisher=Dover Publications Inc. | page=171 | title=Star Names: Their Lore and Meaning | url=https://penelope.uchicago.edu/Thayer/E/Gazetteer/Topics/astronomy/_Texts/secondary/ALLSTA/Coma_Berenices*.html | access-date=2019-11-01 | postscript=. }}</ref> </references>
{{Stars of Coma Berenices}}
<!-- Properties --> [[Category:A-type main-sequence stars]] [[Category:Ap stars]] [[Category:Alpha2 Canum Venaticorum variables]] [[Category:Delta Scuti variables]] <!-- Position/Identifiers --> [[Category:Coma Berenices]] [[Category:Bright Star Catalogue objects|4766]] [[Category:Durchmusterung objects|BD+25 2517]] [[Category:Flamsteed objects|Comae Berenices, 21]] [[Category:Henry Draper Catalogue objects|108945]] [[Category:Hipparcos objects|061071]] [[Category:Objects with variable star designations|Comae Berenices, UU]]