{{Short description|Binary star in the constellation Centaurus}} {{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=π Centauri |x=918|y=808 }} | caption = Location of π Centauri (circled in red) }} {{Starbox observe | epoch = J2000.0 | constell = [[Centaurus]]<ref name=Anderson2012/> | ra = {{RA|11|21|00.41}}<ref name="van Leeuwen2007"/> | dec = {{DEC|−54|29|27.7}}<ref name="van Leeuwen2007"/> | appmag_v = +3.90<ref name=Anderson2012/> {{nowrap|(4.08 + 5.65)}}<ref name=Mason2001/> }} {{Starbox character | type = [[main sequence]] | class = B5Vn<ref name=Hiltner1969/> + B6V<ref name=Edwards1976/> | b-v = {{Val|−0.157|0.015}}<ref name=Anderson2012/> | u-b = | variable = }} {{Starbox astrometry | radial_v = {{Val|+9.4|3.7}}<ref name=Anderson2012/> | prop_mo_ra = {{Val|−35.85|0.34}}< | prop_mo_dec = {{Val|−1.72|0.27}} | pm_footnote = <ref name="van Leeuwen2007"/> | parallax = 9.12 | p_error = 0.34 | parallax_footnote = <ref name="van Leeuwen2007"/> | absmag_v = −1.30<ref name=Anderson2012/> }} {{Starbox orbit | reference = <ref name="Tokovinin2012"/> | period = {{Val|39.0|0.19}} | axis = {{Val|0.2263|0.0011}} | eccentricity = {{Val|0.8530|0.0040}} | inclination = {{Val|19.4|4.9}} | node = {{Val|327.8|3.9}} | periastron = {{Val|2010.410|0.037}} | periarg = {{Val|340.3|4.0}} }} {{Starbox detail | source = | component1 = A | mass = 6.43<ref name="Tokovinin2012"/> | radius = <!-- | luminosity = 783<ref name=Anderson2012/> --> | temperature = 16,760<ref name=Zorec2009/> | gravity = | metal_fe = | rotational_velocity = 340<ref name=vanBelle2012/> | age_myr = 13.9<ref name=Gratton_et_al_2023/> | component2 = B | mass2 = 3.68<ref name="Tokovinin2012"/> }} {{Starbox catalog | names = {{odlist | B=π Cen | CPD=−53°4498 | FK5=428 | HD=98718 | HIP=55425 | HR=4390 | SAO=238986 | CCDM=J11210-5429 | GC=15601 }}<ref name=SIMBAD/> }} {{Starbox reference | Simbad = pi+Cen }} {{Starbox end}}
'''Pi Centauri''' is a [[binary star]] system in the southern [[constellation]] of [[Centaurus]]. Its name is a [[Bayer designation]] that is [[Romanization of Greek|Latinized]] from π Centauri, and abbreviated Pi Cen or π Cen. This pair has a blue-white hue and is visible to the [[naked eye]] with a combined [[apparent visual magnitude]] of +3.90.<ref name=Anderson2012/> The system is located at a distance of approximately 360 [[light year]]s from the Sun based on [[stellar parallax|parallax]],<ref name="van Leeuwen2007"/> and is drifting further away with a [[radial velocity]] of around +9 km/s.<ref name=Anderson2012/> It is a member of the Lower Centaurus–Crux subgroup of the [[Scorpius–Centaurus association]].<ref name=Bobylev2007/>
The magnitude +4.08<ref name=Mason2001/> primary, designated component A, is a [[B-type main-sequence star]] with a [[stellar classification]] of B5Vn,<ref name=Hiltner1969/> where the 'n' suffix indicates broad, diffuse (nebulous) [[absorption line|lines]] due to rapid rotation. This star is spinning with a [[projected rotational velocity]] of 340 km/s, giving it an [[equatorial bulge]] that is 22% larger than the polar radius.<ref name=vanBelle2012/> It has 6.4<ref name="Tokovinin2012"/> times the [[mass of the Sun]] and is radiating 783<ref name=Anderson2012/> times the [[Sun's luminosity]] from its [[photosphere]] at an [[effective temperature]] of 16,760 K.<ref name=Zorec2009/>
The secondary companion, component B, is magnitude +5.65<ref name=Mason2001/> with a class of B6V<ref name=Edwards1976/> and 3.7<ref name="Tokovinin2012"/> times the Sun's mass. The pair orbit around their common [[barycentre]] once every 39 years with an [[orbital eccentricity|eccentricity]] of 0.8530. The [[semi-major axis]] of the companion is 0.23 [[arcsecond]]s at an inclination of 19.4°.<ref name="Tokovinin2012"/>
== References == {{Reflist|refs=
<ref name=SIMBAD>{{cite simbad | title=pi Cen | access-date=2019-10-10 }}</ref>
<ref name=Zorec2009>{{citation | display-authors=1 | last1=Zorec | first1=J. | last2=Cidale | first2=L. | last3=Arias | first3=M. L. | last4=Frémat | first4=Y. | last5=Muratore | first5=M. F. | last6=Torres | first6=A. F. | last7=Martayan | first7=C. | title=Fundamental parameters of B supergiants from the BCD system. I. Calibration of the (λ_1, D) parameters into Teff | journal=Astronomy and Astrophysics | volume=501 | issue=1 | pages=297–320 | date=July 2009 | doi=10.1051/0004-6361/200811147 | postscript=. | bibcode=2009A&A...501..297Z | arxiv=0903.5134 | s2cid=14969137 }}</ref>
<ref name=Edwards1976>{{citation | title=MK classification for visual binary components | last= Edwards | first= T. W. | journal= The Astronomical Journal | postscript=. | date=1976 | volume=81 | pages=245–249 | bibcode=1976AJ.....81..245E | doi=10.1086/111879 }}</ref>
<ref name=vanBelle2012>{{citation | last=van Belle | first=Gerard T. | title=Interferometric observations of rapidly rotating stars | journal=The Astronomy and Astrophysics Review | volume=20 | issue=1 | article-number=51 | date=March 2012 | bibcode=2012A&ARv..20...51V | arxiv=1204.2572 | doi=10.1007/s00159-012-0051-2 | s2cid=119273474 | postscript=. }}</ref>
<ref name=Bobylev2007>{{citation | 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 | bibcode=2007AstL...33..571B | postscript=. |arxiv = 0708.0943 | s2cid=15785349 }}</ref>
<ref name=Hiltner1969>{{citation | display-authors=1 | last1=Hiltner | first1=W. A. | last2=Garrison | first2=R. F. | last3=Schild | first3=R. E. | title=MK Spectral Types for Bright Southern OB Stars | journal=Astrophysical Journal | postscript=. | volume=157 | pages=313–326 | date=July 1969 | doi=10.1086/150069 | bibcode=1969ApJ...157..313H | doi-access=free }}</ref>
<ref name="Tokovinin2012">{{citation | title=Speckle Interferometry and Orbits of "Fast" Visual Binaries | last=Tokovinin | first=Andrei | postscript=. | journal=The Astronomical Journal | volume=144 | issue=2 | at=56 | year=2012 | arxiv=1206.1882 | bibcode=2012AJ....144...56T | doi=10.1088/0004-6256/144/2/56 | s2cid=118586009 }}</ref>
<ref name=Anderson2012>{{cite XHIP | 55425 | mode=cs2 | postscript=. }}</ref>
<ref name=Mason2001>{{citation | display-authors=1 | last1=Mason | first1=Brian D. | last2=Wycoff | first2=Gary L. | last3=Hartkopf | first3=William I. | last4=Douglass | first4=Geoffrey G. | last5=Worley | first5=Charles E. | title=The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog | journal=The Astronomical Journal | postscript=. | volume=122 | issue=6 | pages=3466 | year=2001 | doi=10.1086/323920 | bibcode=2001AJ....122.3466M | doi-access=free }}</ref>
<ref name="van Leeuwen2007">{{citation | title=Validation of the new Hipparcos reduction | last=van Leeuwen | first=F. | journal=Astronomy and Astrophysics | volume=474 | issue=2 | pages=653–664 | year=2007 | arxiv=0708.1752 | bibcode=2007A&A...474..653V | doi=10.1051/0004-6361:20078357 | s2cid=18759600 | postscript=. }}[http://webviz.u-strasbg.fr/viz-bin/VizieR-5?-out.add=.&-source=I/311/hip2&recno=55246 Vizier catalog entry ]</ref>
<ref name=Gratton_et_al_2023>{{citation | postscript=. | title=Multiples among B stars in the Scorpius-Centaurus association | last1=Gratton | first1=R. | last2=Squicciarini | first2=V. | last3=Nascimbeni | first3=V. | last4=Janson | first4=M. | last5=Reffert | first5=S. | last6=Meyer | first6=M. | last7=Delorme | first7=P. | last8=Mamajek | first8=E. E. | last9=Bonavita | first9=M. | last10=Desidera | first10=S. | last11=Mesa | first11=D. | last12=Rigliaco | first12=E. | last13=D'Orazi | first13=V. | last14=Vigan | first14=A. | last15=Lazzoni | first15=C. | last16=Chauvin | first16=G. | last17=Langlois | first17=M. | display-authors=1 | journal=Astronomy & Astrophysics | volume=678 | at=id. A93 | date=October 2023 | doi=10.1051/0004-6361/202346806 | arxiv=2308.09962 | bibcode=2023A&A...678A..93G }}</ref>
}}
{{Stars of Centaurus}} {{DEFAULTSORT:Pi Centauri}} <!-- Physical properties --> [[Category:B-type main-sequence stars]] [[Category:Binary stars]] [[Category:Lower Centaurus Crux]] <!-- Constellation & catalogues --> [[Category:Centaurus]] [[Category:Bayer objects|Centauri, Pi]] [[Category:Bright Star Catalogue objects|4390]] [[Category:Durchmusterung objects|PD-53 4498]] [[Category:Henry Draper Catalogue objects|098718]] [[Category:Hipparcos objects|055425]]