{{Short description|Star in the constellation Centaurus}} {{distinguish|H Centauri}} {{Starbox begin | name=Eta Centauri }} {{Starbox image | image= {{Location mark |image=Centaurus constellation map.svg|alt=|float=center|width=280 |label=|position=right |mark=Red circle.svg|mark_width=12|mark_link=Eta Centauri|x=254|y=461 }} |caption=Location of η Centauri (circled) }}{{Starbox observe | constell = Centaurus | epoch = J2000.0 | ra = {{RA|14|35|30.42416}}<ref name=aaa474_2_653/> | dec = {{DEC|−42|09|28.1708}}<ref name=aaa474_2_653/> | appmag_v = +2.35<ref name=apjs15_459/> {{nowrap|(2.30 - 2.41<ref name=gcvs/>)}} }} {{Starbox character | class = B1.5&nbsp;Vne<ref name=mnras309_1_221/> | b-v = −0.215<ref name=apjs15_459/> | u-b = −0.862<ref name=apjs15_459/> | variable = GCAS<ref name=gcvs/> + LERI }} {{Starbox astrometry | radial_v = −0.2<ref name=scfs/> | prop_mo_ra = −34.73<ref name=aaa474_2_653/> | prop_mo_dec = −32.72<ref name=aaa474_2_653/> | parallax = 10.67 | p_error = 0.21 | parallax_footnote = <ref name=aaa474_2_653/> | absmag_v = −2.53<ref name=Anderson2012/> }} {{Starbox detail | mass = {{Val|12.0|0.3}}<ref name=mnras410_1_190/> | radius = {{Val|6.10|0.12}}<ref name=Arcos2018/> | luminosity = 8,700<ref name=mnras309_1_221/> | temperature = 25,700<ref name=mnras309_1_221/> | metal_fe = | gravity = {{Val|3.95|0.04}}<ref name=Arcos2018/> | age_myr = {{Val|5.6|1.0}}<ref name=mnras410_1_190/> | rotational_velocity = 330<ref name=mnras309_1_221/> }} {{Starbox catalog | names = {{odlist | B=η Cen | CD=−41°8917 | CPD=−41°6839 | FK5=537 | HD=127972 | HIP=71352 | HR=5440 | SAO=225044 }}<ref name=SIMBAD/> }} {{Starbox reference | Simbad=HD+127972 }} {{Starbox end}} '''Eta Centauri''' is a star in the southern constellation of Centaurus. Its name is a Bayer designation that is Latinized from η Centauri, and abbreviated Eta Cen or η Cen. This star has an apparent visual magnitude of +2.35,<ref name=apjs15_459/> which indicates it is readily visible to the naked eye. Based on parallax measurements, it is located at a distance of around {{Convert|306|ly|pc|abbr=off|lk=on}}.<ref name=aaa474_2_653/>

[[File:EtaCenLightCurve.png|thumb|left|A light curve for Eta Centauri, plotted from ''TESS'' data<ref name=MAST/>]] The stellar classification of this star is B1.5&nbsp;Vne,<ref name=mnras309_1_221/> indicating that it is a B-type main sequence star. The 'n' suffix means that the absorption lines are broadened from rapid rotation and the 'e' that it shows emission lines in its spectrum. It has a projected rotational velocity of 330&nbsp;km s<sup>−1</sup><ref name=mnras309_1_221/> and completes a full rotation in less than a day.

As a Be star,<ref name=aas137_3_407/> it has variable emissions in its hydrogen spectral lines. This emission can be modelled by a decretion disk of gas that has been ejected from the star by its rapid rotation and now follows a near-Keplerian orbit around the central body.<ref name=apjs187_1_228/> Its brightness is also slightly variable, and it is classified as a Gamma Cassiopeiae variable star with multiple periods of variability.<ref name=gcvs/> The International Variable Star Index lists Eta Centauri as both a Gamma Cassiopeiae variable and a Lambda Eridani variable with variations caused by its rotation and pulsations.<ref name=vsx/>

Eta Centauri has about 12 times the mass of the Sun,<ref name=mnras410_1_190/> placing it above the dividing line between stars that evolve into white dwarfs and those that turn into supernovae. It is radiating 8,700<ref name=mnras309_1_221/> times the luminosity of the Sun from its outer atmosphere at an effective temperature of 25,700&nbsp;K.<ref name=mnras309_1_221/> At this temperature, the star glows with the blue-white hue common to B-type stars.<ref name=csiro/> Eta Centauri is a proper motion member of the Upper Centaurus–Lupus sub-group in the Scorpius–Centaurus OB association, the nearest such co-moving association of massive stars to the Sun.<ref name=aaa216_1_44/>

In traditional Chinese astronomy, Eta Centauri was known as {{lang|zh|庫樓二}}<ref name=zh/> (meaning: the Second (Star) of ''Koo Low'').<ref name=allen1963/>

== References == <references> <ref name=MAST>{{citation |postscript=. |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=aaa474_2_653>{{citation |postscript=. | title=Validation of the new Hipparcos reduction | last=van Leeuwen | first=F. | journal=Astronomy and Astrophysics | volume=474 | issue=2 |date=November 2007 | pages=653–664 | doi=10.1051/0004-6361:20078357 | bibcode=2007A&A...474..653V |arxiv = 0708.1752 | s2cid=18759600 }}</ref>

<ref name=gcvs>{{citation |postscript=.|bibcode=2009yCat....102025S|title=VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007–2013)|journal=VizieR On-line Data Catalog: B/GCVS |volume=1|pages=02025|last1=Samus|first1=N. N.|last2=Durlevich|first2=O. V.|year=2009|display-authors=etal}}</ref>

<ref name=vsx>{{citation |postscript=.|bibcode= 2006SASS...25...47W|title= The International Variable Star Index (VSX)|journal= The Society for Astronomical Sciences 25th Annual Symposium on Telescope Science. Held May 23–25|volume= 25|pages= 47|last1= Watson|first1= C. L.|year= 2006}}</ref>

<ref name=zh>{{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>

<ref name=Anderson2012>{{cite XHIP | 71352 | mode=cs2 | postscript=. }}</ref>

<ref name=mnras309_1_221>{{citation | postscript=. | last1=Balona | first1=L. A. | last2=Dziembowski | first2=W. A. | title=Excitation and visibility of high-degree modes in stars | journal=Monthly Notices of the Royal Astronomical Society | volume=309 | issue=1 | pages=221–232 |date=October 1999 | doi=10.1046/j.1365-8711.1999.02821.x | bibcode=1999MNRAS.309..221B | doi-access=free }}</ref>

<ref name=allen1963>{{citation | postscript=. | last1=Allen | first1=R. H. | date=1963 | title=Star Names: Their Lore and Meaning | edition=Reprint | publisher=Dover Publications Inc. | location=New York, NY | page=[https://archive.org/details/starnamestheirlo00alle/page/154 154] | title-link=Star Names: Their Lore and Meaning }}</ref>

<ref name=aas137_3_407>{{citation | postscript=. | display-authors=3 | name-list-style=vanc | author=Janot-Pacheco | author2=E. | last3=Leister | first3=N. V. | last4=Hubert | first4=A. M. | last5=Floquet | first5=M. | date=1999 | title=Multi-periodicity of the Be star η Centauri from spectroscopic and photometric observations | journal=Astronomy and Astrophysics Supplement Series | volume=137 | issue=3 | pages=407 | bibcode=1999A&AS..137..407J | doi=10.1051/aas:1999256 | doi-access=free }}</ref>

<ref name=aaa216_1_44>{{citation | postscript=. | display-authors=1 | last1=de Geus | first1=E. J. | last2=de Zeeuw | first2=P. T. | last3=Lub | first3=J. | title=Physical parameters of stars in the Scorpio-Centaurus OB association | journal=Astronomy and Astrophysics | volume=216 | issue=1–2 | pages=44–61 |date=June 1989 | bibcode=1989A&A...216...44D }}</ref>

<ref name=mnras410_1_190>{{citation | postscript=. | display-authors=1 | last1=Tetzlaff | first1=N. | last2=Neuhäuser | first2=R. | last3=Hohle | first3=M. M. | 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 | doi-access=free | bibcode=2011MNRAS.410..190T |arxiv = 1007.4883 | s2cid=118629873 }}</ref>

<ref name=scfs>{{citation | postscript=. | display-authors=1 | title=Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions | journal=Veröff. Astron. Rechen-Inst. Heidelb | volume=35 | last1=Wielen | first1=R. | last2=Schwan | first2=H. | last3=Dettbarn | first3=C. | last4=Lenhardt | first4=H. | last5=Jahreiß | first5=H. | last6=Jährling | first6=R. | publisher=Astronomisches Rechen-Institut Heidelberg | issue=35 | pages=1 | date=1999 | bibcode=1999VeARI..35....1W }}</ref>

<ref name=apjs15_459>{{citation | postscript=. | last1=Gutierrez-Moreno | first1=Adelina | last2=Moreno | first2=Hugo | title=A photometric investigation of the Scorpio-Centaurus association | journal=Astrophysical Journal Supplement Series | volume=15 | page=459 |date=June 1968 | bibcode=1968ApJS...15..459G | doi=10.1086/190168 | doi-access=free }}</ref>

<ref name=SIMBAD>{{cite simbad | title=eta Cen | access-date=2012-03-03 |mode=cs2 | postscript=. }}</ref>

<ref name=csiro>{{citation |postscript=. |title=The Colour of Stars |date=December 21, 2004 |work=Australia Telescope, Outreach and Education |publisher=Commonwealth Scientific and Industrial Research Organisation |url=http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html |access-date=2012-01-16 |url-status=dead |archive-url=https://web.archive.org/web/20120318151427/http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html |archive-date=2012-03-18 }}</ref>

<ref name=apjs187_1_228>{{citation | display-authors=1 | last1=Silaj | first1= J. | last2=Jones | first2=C. E. | last3=Tycner | first3=C. | last4=Sigut | first4=T. A. A. | last5=Smith | first5=A. D. | title=A Systematic Study of Hα Profiles of Be Stars | journal=Astrophysical Journal Supplement Series | volume=187 | issue=1 | pages=228–250 |date=March 2010 | doi=10.1088/0067-0049/187/1/228 | bibcode=2010ApJS..187..228S | s2cid= 122679154 | postscript=. | doi-access=free }}</ref>

<ref name=Arcos2018>{{citation | title=Stellar parameters and H α line profile variability of Be stars in the BeSOS survey | display-authors=1 | postscript=. | last1=Arcos | first1=C. | last2=Kanaan | first2=S. | last3=Chávez | first3=J. | last4=Vanzi | first4=L. | last5=Araya | first5=I. | last6=Curé | first6=M. | journal=Monthly Notices of the Royal Astronomical Society | volume=474 | issue=4 | pages=5287–5299 | date=March 2018 | doi=10.1093/mnras/stx3075 | doi-access=free | bibcode=2018MNRAS.474.5287A | arxiv=1711.08675 }}</ref> </references>

== External links == *{{cite web | title=ETA CEN (Eta Centauri) | publisher=University of Illinois | first1=James B. | last1=Kaler | url=http://stars.astro.illinois.edu/sow/etacen.html | access-date=2018-09-16}} * {{cite archive |first=Leah B. |last=Allen |author-link=Leah B. Allen |item=Study of η Centauri |item-url=https://articles.adsabs.harvard.edu//full/1911phae.proj..686A/0000686.006.html |type=Manuscript |item-id=KG11365.685 |date=1911 |page= |pages=1–50 |fonds= |series= |file= |box= |collection=Project PHAEDRA: Preserving Harvard's Early Data and Research in Astronomy |collection-url=https://library.cfa.harvard.edu/project-phaedra |repository= |institution=Harvard College Observatory |location= |bibcode=1911phae.proj..686A |accession= }}

{{Stars of Centaurus}}

Category:B-type main-sequence stars Category:Be stars Category:Lambda Eridani variables Category:Gamma Cassiopeiae variable stars Category:Upper Centaurus Lupus <!-- Constellation & catalogues --> Category:Centaurus Centauri, Eta 5440 Category:Durchmusterung objects 127972 071352 Category:Brightest stars