{{Short description|Star in the constellation Centaurus}} {{About-distinguish|a Centauri|Alpha Centauri{{!}}α Centauri|HD 100673{{!}}A Centauri|Centaurus A}} {{Starbox begin}} {{Starbox image | image = {{Location mark |image=Centaurus constellation map.svg|alt=|float=center|width=280 |label=|position=right |mark=Red circle.svg|mark_width=10|mark_link=HD 125823 |x=300|y=392 }} | caption = Location of a Centauri (circled in red) }} {{Starbox observe | epoch = J2000.0 | constell = [[Centaurus]]<ref name=Anderson_Francis_2012/> | ra = {{RA|14|23|02.24}}<ref name="van Leeuwen2007"/> | dec = {{DEC|−39|30|42.5}}<ref name="van Leeuwen2007"/> | appmag_v = +4.41<ref name=Anderson_Francis_2012/> }} {{Starbox character | type = [[main sequence]]<ref name=dr3/><ref name=Walczak2024/> | class = B2V<ref name=houk1979/> | b-v = −0.19<ref name=cousins1971/> | u-b = −0.75<ref name=cousins1971/> | variable = [[SX Arietis variable|SX Ari]]<ref name=Samus_et_al_2017/> }} {{Starbox astrometry | radial_v = {{val|+7.13|0.16}}<ref name=Soubiran2018/> | prop_mo_ra = {{val|−24.15|0.13}}<ref name="van Leeuwen2007"/> | prop_mo_dec = {{val|−21.90|0.13}}<ref name="van Leeuwen2007"/> | parallax = 7.13 | p_error = 0.16 | parallax_footnote = <ref name="van Leeuwen2007"/> | absmag_v = −1.27<ref name=aaa334_181/> }} {{Starbox detail | source = | mass = {{val|5.4501|0.0067}}<ref name=Walczak2024/> | radius = {{val|3.0071|0.0054}}<ref name=Walczak2024/> | luminosity = {{Val|1019|9|fmt=commas}}<ref name=Walczak2024/> | temperature = {{Val|18863|57|56|fmt=commas}}<ref name=Walczak2024/> | metal_fe = | gravity = {{val|4.20|0.12}}<ref name=aaa334_181/> | rotational_velocity = 16.0<ref name=makarenko2021/> | rotation = 8.817744 days<ref name=aaa334_181/><ref name=Bohlender_et_al_2010/> | age_myr = {{Val|23.61|0.13}}<ref name=Walczak2024/> }} {{Starbox catalog | names = {{odlist | name=Bidelman's Helium Variable Star<ref name=Jaschek_et_al_1968/> | V=V761 Centauri | B=a Centauri | CD=−38 9329 | HD=125823 | HIP=70300 | HR=5378 | SAO=205497 }}<ref name=SIMBAD/> }} {{Starbox reference | Simbad = HD+125823 }} {{Starbox end}}
'''HD 125823''', also known as '''V761 Centauri''' or '''a Centauri''', is a [[variable star]] in the [[constellation]] [[Centaurus]]. It is a blue-white star that is visible to the [[naked eye]] with a mean [[apparent visual magnitude]] of +4.41. The distance to this star is approximately 460 [[light year]]s based on [[stellar parallax|parallax]] measurements.<ref name="van Leeuwen2007"/> It is a member of the Upper Centaurus–Lupus subgroup of the [[Scorpius–Centaurus association]].<ref name=Bobylev_Bajkova_2007/>
[[File:V761CenLightCurve.png|thumb|left|250px|A [[light curve]] V761 Centauri, plotted from ''[[Hipparcos]]'' data<ref name=HipDataAccess/>]]
In 1965, [[William P. Bidelman|W. P. Bidelman]] discovered that the intensities of the star's neutral helium lines had varied on photographic plates taken over the period 1908 to 1911. This variation was confirmed by [[A. David Thackeray|A. D. Thackeray]] in 1966.<ref name=Jaschek_et_al_1968/> The star ranges from a [[helium-strong]] B2 class to a [[helium-weak]] B8 with a period of 8.82 days.<ref name=Hubrig_González_2007/> Radial velocity measurements during the 1970s showed differing velocity variations for helium and other elements.<ref name=Underhill_et_al_1973/> The magnetic field strength peaks at a negative maximum in phase with the maximum helium line strength.<ref name=Hubrig_González_2007/> Weak emission has been detected in the singly-ionized lines of silicon, magnesium, and iron, but not in the neutral lines of hydrogen and helium.<ref name=Hubrig_González_2007/>
This is a magnetic peculiar [[Bp star]] that shows periodic variation in the strength of its neutral helium lines. It is classified as an [[SX Arietis variable|SX Arietis type]] [[variable star]] and its brightness varies from magnitude +4.38 to +4.43 with a period of 8.82 days.<ref name=Samus_et_al_2017/> The star displays very different helium abundances between the two hemispheres, and, unusually, helium-3 has been detected in the weaker southern hemisphere. Latitudinal abundance concentrations have been found for iron, nitrogen, and oxygen.<ref name=Bohlender_et_al_2010/> The variation in helium concentration effects the density [[scale height]] of the atmosphere, causing helium rich regions to have a lower luminosity in the visual band but emitting stronger levels of far ultraviolet.<ref name=Krtička_et_al_2020/>
==References== <references> <ref name=dr3>{{cite Gaia DR3|6116497702589633152}}</ref>
<ref name=HipDataAccess>{{cite web |title=Hipparcos Tools Interactive Data Access |url=https://www.cosmos.esa.int/web/hipparcos/interactive-data-access |website=Hipparcos |publisher=ESA |access-date=8 December 2021}}</ref>
<ref name=SIMBAD>{{Cite simbad | title=HD 125823 | access-date=2021-10-08 }}</ref>
<ref name=cousins1971>{{cite journal |bibcode=1971ROAn....7.....C |title=Photometric standard stars |last1=Cousins |first1=A. W. J. |journal=Royal Observatory Annals |date=1971 |volume=7 }}</ref>
<ref name=Anderson_Francis_2012>{{cite journal | last1=Anderson | first1=E. | last2=Francis | first2=Ch. | title=XHIP: An extended hipparcos compilation | 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=makarenko2021>{{cite journal |bibcode=2021MNRAS.504.5813M |title=Testing the fossil field hypothesis: Could strongly magnetized OB stars produce all known magnetars? |last1=Makarenko |first1=Ekaterina I. |last2=Igoshev |first2=Andrei P. |last3=Kholtygin |first3=A. F. |journal=Monthly Notices of the Royal Astronomical Society |date=2021 |volume=504 |issue=4 |page=5813 |doi=10.1093/mnras/stab1175 |doi-access=free |arxiv=2104.10579 }}</ref>
<ref name=Walczak2024>{{Cite journal |last1=Walczak |first1=Przemysław |last2=Kopacz |first2=Agnieszka |date=2024-03-23 |title=Asteroseismic modelling of the chemically peculiar B-type pulsator with an asymptotic period spacing – a Cen |journal=Monthly Notices of the Royal Astronomical Society |language=en |volume=529 |issue=4 |pages=4176–4191 |doi=10.1093/mnras/stae672 |doi-access=free |issn=0035-8711}}</ref>
<ref name=aaa334_181>{{cite journal | last1=North | first1=P. | title=Do SI stars undergo any rotational braking? | journal=Astronomy and Astrophysics | volume=334 | pages=181–187 | date=June 1998 | bibcode=1998A&A...334..181N | arxiv=astro-ph/9802286 }}</ref>
<ref name="van Leeuwen2007">{{cite journal | title=Validation of the new Hipparcos reduction | 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=70061 Vizier catalog entry ]</ref>
<ref name=Soubiran2018>{{cite journal | title=Gaia Data Release 2. The catalogue of radial velocity standard stars | last1=Soubiran | first1=C. | last2=Jasniewicz | first2=G. | last3=Chemin | first3=L. | last4=Zurbach | first4=C. | last5=Brouillet | first5=N. | last6=Panuzzo | first6=P. | last7=Sartoretti | first7=P. | last8=Katz | first8=D. | last9=Le Campion | first9=J. -F. | last10=Marchal | first10=O. | last11=Hestroffer | first11=D. | last12=Thévenin | first12=F. | last13=Crifo | first13=F. | last14=Udry | first14=S. | last15=Cropper | first15=M. | last16=Seabroke | first16=G. | last17=Viala | first17=Y. | last18=Benson | first18=K. | last19=Blomme | first19=R. | last20=Jean-Antoine | first20=A. | last21=Huckle | first21=H. | last22=Smith | first22=M. | last23=Baker | first23=S. G. | last24=Damerdji | first24=Y. | last25=Dolding | first25=C. | last26=Frémat | first26=Y. | last27=Gosset | first27=E. | last28=Guerrier | first28=A. | last29=Guy | first29=L. P. | last30=Haigron | first30=R. | display-authors=1 | journal=Astronomy and Astrophysics | volume=616 | pages=A7 | year=2018 | bibcode=2018A&A...616A...7S | arxiv=1804.09370 | doi=10.1051/0004-6361/201832795 | s2cid=52952408 }}</ref>
<ref name=Jaschek_et_al_1968>{{cite journal | title=On the Spectrum of Bidelman's Helium Variable Star HD 125823 | last1=Jaschek | first1=C. | last2=Jaschek | first2=M. | last3=Morgan | first3=W. W. | last4=Slettebak | first4=Arne | display-authors=1 | journal=Astrophysical Journal | volume=153 | page=L87 | date=August 1968 | doi=10.1086/180227 | bibcode=1968ApJ...153L..87J | doi-access=free }}</ref>
<ref name=Underhill_et_al_1973>{{cite journal | title=The radial velocity variations of HD 125823 a Centauri | display-authors=1 | last1=Underhill | first1=A. B. | last2=Klinglesmith | first2=D. A. | last3=Frey | first3=H. | journal=Astronomy and Astrophysics | volume=25 | page=141 | date=May 1973 | bibcode=1973A&A....25..141U }}</ref>
<ref name=Hubrig_González_2007>{{cite journal | title=Detection of variable Si II, Mn II, and Fe II emission lines in the magnetic Bp star a Centauri | last1=Hubrig | first1=S. | last2=González | first2=J. F. | journal=Astronomy and Astrophysics | volume=466 | issue=3 | date=May 2007 | pages=1083–1087 | bibcode=2007A&A...466.1083H | arxiv=astro-ph/0703229 | doi=10.1051/0004-6361:20066738 | s2cid=15414222 }}</ref>
<ref name=Bohlender_et_al_2010>{{cite journal | title=Doppler imaging of the helium-variable star a Centauri | display-authors=1 | last1=Bohlender | first1=D. A. | last2=Rice | first2=J. B. | last3=Hechler | first3=P. | journal=Astronomy and Astrophysics | volume=520 | id=A44 | pages=9 | date=September 2010 | arxiv=1007.0977 | bibcode=2010A&A...520A..44B | doi=10.1051/0004-6361/201014157 | s2cid=118374769 }}</ref>
<ref name=Krtička_et_al_2020>{{cite journal | title=Distorted surfaces of magnetic helium-peculiar stars: an application to a Cen | last1=Krtička | first1=J. | last2=Mikulášek | first2=Z. | last3=Prvák | first3=M. | last4=Niemczura | first4=E. | last5=Leone | first5=F. | last6=Wade | first6=G. | display-authors=1 | journal=Monthly Notices of the Royal Astronomical Society | volume=493 | issue=2 | pages=2140–2148 | date=April 2020 | doi=10.1093/mnras/staa378 | doi-access=free | arxiv=2002.01385 | bibcode=2020MNRAS.493.2140K }}</ref>
<ref name=Bobylev_Bajkova_2007>{{cite journal | title=Kinematics of the Scorpius–Centaurus OB association | last1=Bobylev | first1=V. V. | last2=Bajkova | first2=A. T. | journal=Astronomy Letters | volume=33 | issue=9 | pages=571–583 | date=September 2007 | doi=10.1134/S1063773707090010 | arxiv=0708.0943 | bibcode=2007AstL...33..571B | s2cid=15785349 }}</ref>
<ref name=houk1979>{{cite book | last1=Houk | first1=Nancy | title=Michigan catalogue of two-dimensional spectral types for the HD stars | volume=3 | date=1979 | publication-place=Ann Arbor, Michigan | publisher=Dept. of Astronomy, University of Michigan | bibcode=1982mcts.book.....H }}</ref>
<ref name=Samus_et_al_2017>{{cite journal | display-authors=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. | title=General Catalogue of Variable Stars | version=GCVS 5.1 | journal=Astronomy Reports | year=2017 | volume=61 | issue=1 | pages=80–88 | bibcode=2017ARep...61...80S | s2cid=125853869 | url=http://www.sai.msu.su/gcvs/cgi-bin/search.cgi?search=V761+Cen | accessdate=2021-10-10 | doi=10.1134/S1063772917010085 | url-access=subscription }}</ref> </references>
{{Stars of Centaurus}}
<!-- Properties --> [[Category:Ap stars]] [[Category:SX Arietis variables]] <!-- Other --> [[Category:Centaurus]] [[Category:Bayer objects|Centauri, a]] [[Category:Durchmusterung objects|CD-38 09329]] [[Category:Henry Draper Catalogue objects|125823]] [[Category:Hipparcos objects|070300]] [[Category:Bright Star Catalogue objects|5378]] [[Category:Objects with variable star designations|Centauri, V761]] [[Category:B-type main-sequence stars]]