{{Short description|Star in the constellation Coma Berenices}} {{Starbox begin | name = [[Bayer designation|α&nbsp;Comae&nbsp;Berenices]] }} {{Starbox image | image = {{Location mark | image = Coma Berenices constellation map.svg | width = 250 | alt = Map of the constellation Coma Berenices | float = center | mark = Red circle.svg | mark_width = 10 | x = 130 | y = 569 }} | caption = α&nbsp;Comae&nbsp;Berenices (circled) in the constellation Coma Berenices }} {{Starbox observe | epoch = J2000 | constell = [[Coma Berenices]] | ra = {{RA|13|09|59.285}}<ref name="van Leeuwen2007"/> | dec = {{DEC|+17|31|46.04}}<ref name="van Leeuwen2007"/> | appmag_v=4.29&nbsp;to&nbsp;4.35<br /><small>(combined)</small><ref name=nsv1>NSV 6116, database entry, [http://www.sai.msu.su/groups/cluster/gcvs/gcvs/nsv/nsv.dat New Catalogue of Suspected Variable Stars, the improved version], Sternberg Astronomical Institute, Moscow, Russia. Accessed on line September 3, 2008.</ref><br />A: 4.85 / B: 5.53<ref name=orb /> }} {{Starbox character | class = A: F5V / B: F5V<br /><small>(binary star)</small><ref name=kaler/> | u-b = −0.06<ref name=bsc2>[http://webviz.u-strasbg.fr/viz-bin/VizieR-5?-out.add=.&-source=V/50/catalog&recno=4968 HR 4968], database entry, The Bright Star Catalogue, 5th Revised Ed. (Preliminary Version), D. Hoffleit and W. H. Warren, Jr., [[Centre de Données astronomiques de Strasbourg|CDS]] ID [http://vizier.u-strasbg.fr/viz-bin/Cat?V/50 V/50]. Accessed on line September 3, 2008.</ref> | b-v = 0.45<ref name=bsc2 /> | v-r = 0.2<ref name=sb0 /> | r-i = 0.2<ref name=sb0 /> }} {{Starbox astrometry | radial_v = {{val|−17.7|0.9}}<ref name=sb0 /> | prop_mo_ra = {{val|−433.13|0.70}}<ref name="van Leeuwen2007"/> | prop_mo_dec = {{val|141.24|0.51}}<ref name="van Leeuwen2007"/> | parallax = 56.10 | p_error = 0.89 | parallax_footnote = <ref name="van Leeuwen2007"/> | absmag_v= 3.82<ref name=Reiners2006/> }} {{Starbox orbit | reference = <ref name="Muterspaugh2015"/> | period = {{val|25.8696|0.008219}} | axis = {{val|0.67144|0.00033}} | periastron = {{val|57056.84|0.36}} | inclination = {{val|90.0501|0.0062}} | node = {{val|12.2272|0.0098}} | eccentricity = {{val|0.51060|0.00061}} | periarg = {{val|100.563|0.026}} }} {{Starbox detail | component1 = A | mass = 1.237<ref name=pavlovic/> | luminosity = 1.72<ref name=brummelaar/> | temperature = 6,365<ref name=pastel/> | metal_fe = {{val|-0.23}}<ref name=pastel/> | gravity = 4.19<ref name=pastel/> | component2 = B | mass2 = 1.087<ref name=pavlovic/> | temperature2 = 6,378<ref name=brummelaar/> | luminosity2 = 1.75<ref name=brummelaar/> }} {{Starbox catalog | names={{odlist | name=Diadem | B=α Com | F=42 Com | ADS=8804 | BD=+18 2697 | CCDM=J13100+1732 | GC=17833 | GJ=501 | HIP=64241 | LTT=13802 | NLTT=33105 | PPM=129630 | SAO=100443 | WDS=J13100+1732}}, [[Double star designation|STF 1728]], [[Index Catalogue of Visual Double Stars|IDS]]&nbsp;13051+1803&nbsp;AB<ref name=sb0 /> | component1 = A | names1={{odlist | HD=114378 | HR=4968}}<ref>{{SIMBAD link|HD+114378|HD 114378 -- Star in double system}}, database entry, [[SIMBAD]], accessed on line September 3, 2008.</ref> | component2 = B | names2={{odlist | HD=114379 | HR=4969}}<ref>{{SIMBAD link|HD+114379|HD 114379 -- Star in double system}}, database entry, [[SIMBAD]], accessed on line September 3, 2008.</ref> }} {{Starbox reference | Simbad=alf+Com |sn=The system | Simbad2=alf+Com+A |sn2=A | Simbad3=alf+Com+B |sn3=B }} {{Starbox end}}

'''Alpha Comae Berenices''' ('''α Comae Berenices''', abbreviated '''Alpha Com''', '''α Com''') is a [[binary star]] in the northern [[constellation]] of [[Coma Berenices]] ([[Berenice II of Egypt|Berenice]]'s Hair), {{convert|17.8|pc|ly}} away. It consists of two [[main sequence]] stars, each a little hotter and more luminous than the Sun.

Alpha Comae Berenices is said to represent the crown worn by Queen Berenice. The two components are designated Alpha Comae Berenices A (officially named '''Diadem''' {{IPAc-en|'|d|ai|@|d|E|m}}, the traditional name for the system)<ref name="IAU-LSN">{{cite web | url=https://www.iau.org/public/themes/naming_stars/ | title=Naming Stars | publisher=IAU.org | access-date=16 December 2017 | archive-date=10 March 2025 | archive-url=https://web.archive.org/web/20250310063743/https://www.iau.org/public/themes/naming_stars/ | url-status=dead }}</ref> and B.

== Nomenclature == ''α Comae Berenices'' ([[Latinisation of names|Latinised]] to ''Alpha Comae Berenices'') is the system's [[Bayer designation]]. The designations of the two components as ''Alpha Comae Berenices A'' and ''B'' derive from the convention used by the Washington Multiplicity Catalog (WMC) for [[Star system|multiple star system]]s, and adopted by the [[International Astronomical Union]] (IAU).<ref name="planetnaming">{{cite arXiv |title=On the naming convention used for multiple star systems and extrasolar planets |date=2010 |eprint=1012.0707 |class=astro-ph.SR |last1= Hessman |first1=F. V. |last2= Dhillon |first2=V. S. |last3= Winget |first3=D. E. |last4= Schreiber |first4=M. R. |last5= Horne |first5=K. |last6= Marsh |first6=T. R. |last7= Guenther |first7=E. |last8= Schwope |first8=A. |last9= Heber |first9=U. }}</ref>

The system has the proper name ''Diadem'', of unknown modern origin.<ref name=kaler/> In 2016, the [[International Astronomical Union]] organized a [[IAU Working Group on Star Names|Working Group on Star Names]] (WGSN)<ref>{{Cite web|url=https://www.iau.org/science/scientific_bodies/working_groups/280/|title=International Astronomical Union {{!}} IAU|website=www.iau.org|access-date=2017-03-31|archive-date=2016-06-10|archive-url=https://web.archive.org/web/20160610172014/https://www.iau.org/science/scientific_bodies/working_groups/280/|url-status=dead}}</ref> to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire [[multiple star|multiple systems]].<ref name="TriRpt18">{{cite web | url=https://www.iau.org/static/science/scientific_bodies/working_groups/280/wg-starnames-triennial-report-2015-2018.pdf | page=5 | title=WG Triennial Report (2015-2018) - Star Names | access-date=2018-07-14 | archive-date=2022-10-09 | archive-url=https://ghostarchive.org/archive/20221009/https://www.iau.org/static/science/scientific_bodies/working_groups/280/wg-starnames-triennial-report-2015-2018.pdf | url-status=dead }}</ref> It approved the name ''Diadem'' for the component Alpha Comae Berenices A on 1 February 2017 and it is now so included in the List of IAU-approved Star Names.<ref name="IAU-LSN"/>

In [[Chinese astronomy|Chinese]], {{lang|zh|太微左垣}} ({{lang|zh-Latn|Tài Wēi Zuǒ Yuán}}), meaning ''[[Supreme Palace enclosure|Left Wall of Supreme Palace Enclosure]]'', refers to an [[asterism (astronomy)|asterism]] consisting of Alpha Comae Berenices, [[Eta Virginis]], [[Gamma Virginis]], [[Delta Virginis]] and [[Epsilon Virginis]].<ref>{{in lang|zh}} ''中國星座神話'', written by 陳久金. Published by 台灣書房出版有限公司, 2005, {{ISBN|978-986-7332-25-7}}.</ref> Consequently, the [[Chinese star names|Chinese name]] for Alpha Comae Berenices itself is {{lang|zh|太微左垣五}} ({{lang|zh-Latn|Tài Wēi Zuǒ Yuán wǔ}}, {{langx|en|the Fifth Star of Left Wall of Supreme Palace Enclosure}}.),<ref>{{in lang|zh}} [http://www.lcsd.gov.hk/CE/Museum/Space/Research/StarName/c_research_chinengstars_c_d.htm 香港太空館 - 研究資源 - 亮星中英對照表] {{webarchive|url=https://web.archive.org/web/20090929163750/http://www.lcsd.gov.hk/CE/Museum/Space/Research/StarName/c_research_chinengstars_c_d.htm |date=2009-09-29 }}, Hong Kong Space Museum. Accessed on line November 23, 2010.</ref> representing {{lang|zh|東上將}} ({{lang|zh-Latn|Dōngshǎngjiāng}}), meaning ''The First Eastern General''.<ref>{{in lang|zh}} [http://www.lcsd.gov.hk/CE/Museum/Space/Research/StarName/e_research_chinengstarzone_b.htm#SupremePalaceEnclosure English-Chinese Glossary of Chinese Star Regions, Asterisms and Star Name] {{webarchive|url=https://web.archive.org/web/20080924022136/http://www.lcsd.gov.hk/CE/Museum/Space/Research/StarName/e_research_chinengstarzone_b.htm |date=2008-09-24 }}, Hong Kong Space Museum. Accessed on line November 23, 2010.</ref> 東上將 (Dōngshǎngjiāng), westernized into ''Shang Tseang'', but that name was designated for "v Comae Berenices" by R.H. Allen and the meaning is "a Higher General".<ref>[https://penelope.uchicago.edu/Thayer/E/Gazetteer/Topics/astronomy/_Texts/secondary/ALLSTA/Coma_Berenices*.html Richard Hinckley Allen: Star Names — Their Lore and Meaning: Coma Berenices]</ref>

==Properties== Although Alpha Comae Berenices bears the title "[[alpha]]", at [[apparent magnitude|magnitude]] 4.32 it is actually fainter than [[Beta Comae Berenices]].

It is a [[binary star]], with almost equal components of magnitudes 5.05 m and 5.08 m [[orbit]]ing each other with a [[orbital period|period]] of 25.87 years. The system, estimated to be 58 [[light-years]] distant, appears so nearly "edge-on" from the Earth that the two stars appear to move back-and-forth in a straight line with a maximum separation of only 0.7 arcsec. Eclipses are predicted to occur between the two components, however they have not been successfully observed due to miscalculations of the time of eclipse. If eclipses do occur, the next [[primary eclipse]] is expected to be around 27 September 2040; the next date for a [[secondary eclipse]], which has only a 3.3% probability of happening, is 11 January 2026.<ref name="Muterspaugh2015"/>

The mean separation between them is approximately 10 [[Astronomical unit|AU]], about the distance between the Sun and [[Saturn]].

The binary star has a [[double star|visual companion]], CCDM J13100+1732C, of apparent magnitude 10.2, located 89 [[arcsecond]]s away along a position angle of 345°.<ref name=wds>Entry 13100+1732, discoverer code STF1728, components AB-C, [http://ad.usno.navy.mil/wds/wdsnewframe3.html The Washington Double Star Catalog] {{webarchive|url=https://web.archive.org/web/20080413021643/http://ad.usno.navy.mil/wds/wdsnewframe3.html |date=2008-04-13 }}, [[United States Naval Observatory]]. Accessed on line September 3, 2008.</ref>

Alpha Comae Berenicis forms an isosceles triangle with globular star clusters [[Messier 53]] and [[NGC 5053]]. The apparent diameter of this triangle is a little more than one degree. The location of Alpha Comae Berenicis is westward (preceding) of both globular star clusters.

==References== <references> <ref name="Muterspaugh2015">{{cite journal | title=Predicting the α Comae Berenices Time of Eclipse: How 3 Ambiguous Measurements out of 609 Caused a 26 Year Binary's Eclipse to be Missed | last1=Muterspaugh | first1=Matthew W. | last2=Wijngaarden | first2=M. J. P. | last3=Henrichs | first3=H. F. | last4=Lane | first4=Benjamin F. | last5=Hartkopf | first5=William I. | last6=Henry | first6=Gregory W. | last7=Schaefer | first7=Gail H. | last8=Farrington | first8=Chris | last9=Hummel | first9=Christian A. | last10=Zavala | first10=R. T. | display-authors=1 | journal=The Astronomical Journal | volume=150 | issue=5 | at=140 | date=2015 | arxiv=1501.05639 | bibcode=2015AJ....150..140M | doi=10.1088/0004-6256/150/5/140 | s2cid=119282868 }}</ref>

<ref name=Reiners2006>{{citation | last1=Reiners | first1=Ansgar | title=Rotation- and temperature-dependence of stellar latitudinal differential rotation | journal=Astronomy and Astrophysics | volume=446 | issue=1 |date=January 2006 | pages=267–277 | doi=10.1051/0004-6361:20053911 | bibcode=2006A&A...446..267R |arxiv = astro-ph/0509399 | s2cid=8642707 }}</ref>

<ref name=orb>Entry 13100+1732, [http://ad.usno.navy.mil/wds/orb6/orb6orbits.txt Sixth Catalog of Orbits of Visual Binary Stars] {{Webarchive|url=https://web.archive.org/web/20050424035159/http://ad.usno.navy.mil/wds/orb6/orb6orbits.txt |date=2005-04-24 }}, [[United States Naval Observatory]]. Accessed on line September 3, 2008.</ref>

<ref name=sb0>{{SIMBAD link|alf+com|NSV 6116 -- Variable Star}}, database entry, [[SIMBAD]]. Accessed on line September 3, 2008.</ref>

<ref name="van Leeuwen2007">{{cite journal | title=Validation of the new Hipparcos reduction | url=http://www.aanda.org/articles/aa/abs/2007/41/aa8357-07/aa8357-07.html | last1=van Leeuwen | first1=F. | journal=Astronomy and Astrophysics | volume=474 | issue=2 | pages=653–664 | date=2007 | arxiv=0708.1752 | bibcode=2007A&A...474..653V | doi=10.1051/0004-6361:20078357 | s2cid=18759600 }} [http://webviz.u-strasbg.fr/viz-bin/VizieR-5?-out.add=.&-source=I/311/hip2&recno=64022 Vizier catalog entry ]</ref>

<ref name=pavlovic>{{cite journal|bibcode=2005SerAJ.170...73P|title=Orbits of Seven Edge-On Visual Double Stars|journal=Serbian Astronomical Journal|volume=170|pages=73–78|last1=Pavlovic|first1=R.|last2=Todorovic|first2=N.|year=2005|issue=170|doi=10.2298/SAJ0570073P|doi-access=free}}</ref>

<ref name=brummelaar>{{cite journal|bibcode=2000AJ....119.2403T|title=Binary Star Differential Photometry Using the Adaptive Optics System at Mount Wilson Observatory|journal=The Astronomical Journal|volume=119|issue=5|pages=2403|last1=Ten Brummelaar|first1=Theo|last2=Mason|first2=Brian D.|last3=McAlister|first3=Harold A.|last4=Roberts|first4=Lewis C.|last5=Turner|first5=Nils H.|last6=Hartkopf|first6=William I.|last7=Bagnuolo|first7=William G.|year=2000|doi=10.1086/301338|doi-access=free}}</ref>

<ref name=pastel>{{cite journal|bibcode=2016A&A...591A.118S|title=The PASTEL catalogue: 2016 version|journal=Astronomy and Astrophysics|volume=591|pages=A118|last1=Soubiran|first1=Caroline|last2=Le Campion|first2=Jean-François|last3=Brouillet|first3=Nathalie|last4=Chemin|first4=Laurent|year=2016|doi=10.1051/0004-6361/201628497|arxiv=1605.07384|s2cid=119258214}}</ref>

<ref name=kaler>{{cite web |last=Kaler |first=Jim |author-link=Jim Kaler |date=2008-05-11 |title=Diadem |url=http://stars.astro.illinois.edu/sow/diadem.html}}</ref> </references>

== External links == {{Sky|13|09|59.285|+|17|31|46.04}} {{Stars of Coma Berenices}}

[[Category:Bayer objects|Comae Berenices, Alpha]] [[Category:Binary stars]] [[Category:Coma Berenices]] [[Category:F-type main-sequence stars]] [[Category:Stars with proper names|Diadem]] [[Category:Flamsteed objects|Comae Berenices, 42]] [[Category:Henry Draper Catalogue objects|114378]] [[Category:Hipparcos objects|064241]] [[Category:Triple stars]] [[Category:Durchmusterung objects|BD+18 2697]] [[Category:Gliese and GJ objects|0501]] [[Category:Bright Star Catalogue objects|4968]]