HD 125823
{{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 = 250px
| caption = A light curve V761 Centauri, plotted from Hipparcos data
}}
{{Starbox observe
| epoch = J2000.0
| constell = Centaurus
}}
{{Starbox character
| type = main sequence
| variable = SX Ari
}}
{{Starbox astrometry
| radial_v = {{val|+7.13|0.16}}
| prop_mo_ra = {{val|−24.15|0.13}}
| prop_mo_dec = {{val|−21.90|0.13}}
| parallax = 7.13
| p_error = 0.16
}}
{{Starbox detail
| metal_fe =
}}
{{Starbox catalog
| names = {{odlist | V=V761 Centauri | B=a Centauri | CD=−38 9329 | HD=125823 | HIP=70300 | HR=5378 | SAO=205497 }}
}}
{{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 years based on parallax measurements. It is a member of the Upper Centaurus–Lupus subgroup of the Scorpius–Centaurus association.
In 1965, 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. D. Thackeray in 1966. The star ranges from a helium-strong B2 class to a helium-weak B8 with a period of 8.82 days. Radial velocity measurements during the 1970s showed differing velocity variations for helium and other elements. The magnetic field strength peaks at a negative maximum in phase with the maximum helium line strength. 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.
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 type variable star and its brightness varies from magnitude +4.38 to +4.43 with a period of 8.82 days. 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. 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.
References
{{reflist|refs=
{{cite Gaia DR3|6116497702589633152}}
{{Cite simbad | title=HD 125823 | access-date=2021-10-08 }}
| 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 }}
| 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 }}
| 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 ]
| 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 }}
| 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 }}
| 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 }}
| 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 }}
| 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 }}
| 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 }}
| 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 }}
| 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 }}
| 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 }}
}}
{{Stars of Centaurus}}
{{DEFAULTSORT:HD 125823}}