{{Short description|Star in the constellation Centaurus}} {{about-distinguish|g Centauri|G Centauri}} {{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=2 Centauri |x=435|y=268 }} | caption = Location of 2 Centauri (circled in red) }} {{Starbox observe | epoch= J2000.0 | constell = [[Centaurus]] | ra = {{RA|13|49|26.72175}}<ref name="van Leeuwen2007"/> | dec = {{DEC|−34|27|02.7929}}<ref name="van Leeuwen2007"/> | appmag_v = 4.16–4.26<ref name=gcvs/> }} {{Starbox character | type = [[asymptotic giant branch|AGB]]<ref name=eggen1992/> | class = M5 III<ref name=HD/> | b-v = +1.49<ref name=EgUBV/> | u-b = +1.44<ref name=EgUBV/> | variable = [[semiregular variable star|SRb]]<ref name=gcvs/> }} {{Starbox astrometry | radial_v = {{Val|+40.7|0.7}}<ref name=RV/> | prop_mo_ra = {{Val|−41.68|0.23}}<ref name="van Leeuwen2007"/> | prop_mo_dec = {{Val|−59.77|0.18}}<ref name="van Leeuwen2007"/> | parallax = 17.82 | p_error = 0.21 | parallax_footnote = <ref name="van Leeuwen2007"/> | absmag_v = +0.51<ref name=Cardini2005/> }} {{Starbox detail | source = | mass = 1.0<ref name=ayres2024/> | radius = 82.4<ref>{{Cite journal |last1=Wood |first1=Brian E. |last2=Harper |first2=Graham M. |last3=Müller |first3=Hans-Reinhard |date=May 2024 |title=Resolving Red Giant Winds with the Hubble Space Telescope* |journal=The Astrophysical Journal |language=en |volume=967 |issue=2 |pages=120 |doi=10.3847/1538-4357/ad401f |doi-access=free |issn=0004-637X|arxiv=2404.15086 }}</ref> | luminosity = 767<ref name=ayres2024/> | temperature = 3,438<ref name=ayres2024/> | metal_fe = | gravity = 0.65<ref name=ayres2024/> | rotational_velocity = | age_gyr = }} {{Starbox catalog | names = {{odlist | V=V806 Cen | B=g Centauri | F=2 Cen | CD=−33°9358 | HD=120323 | HIP=67457 | HR=5192 | SAO=204875 | GC=18666 }}<ref name=Simbad/> }} {{Starbox reference | Simbad = HD+120323 }} {{Starbox end}}
'''2 Centauri''' is a single<ref name=Eggleton2008/> [[star]] in the [[Southern celestial hemisphere|southern]] [[constellation]] of [[Centaurus]], located approximately 183 [[light-year]]s from [[Earth]].<ref name="van Leeuwen2007"/> It has the [[Bayer designation]] '''g Centauri''';<ref name=Simbad/> ''2 Centauri'' is the [[Flamsteed designation]]. This object is visible to the [[naked eye]] as faint, red-hued star with an [[apparent visual magnitude]] of about 4.2. It is moving away from the Earth with a heliocentric [[radial velocity]] of +41 km/s.<ref name=RV/> The star is a member of the [[HR 1614]] supercluster.<ref name="Eggen1998"/>
[[File:V806CenLightCurve.png|thumb|left|250px|A [[light curve]] for V806 Centauri. The main plot shows the long term variability from ''[[Hipparcos]]'' data,<ref name=HipDataAccess/> and the inset plot shows the variability over the 26.5 day period, using data from Tabur ''et al.'' (2009).<ref name="Tabur"/> The green curve shows the best-fit sine wave, which has an amplitude of 18 millimagnitudes.]]
This is an [[stellar evolution|evolved]] [[red giant]] star with a [[stellar classification]] of M5 III.<ref name=HD/> In 1951, [[Alan William James Cousins]] announced that the star, then called g Centauri, is a [[variable star]].<ref name="Cousins1951"/> It was given its [[variable star designation]], V806 Centauri, in 1978.<ref name="Kholopov1978"/> It is classified as a [[semiregular variable star|semiregular]] [[variable star]] and its brightness varies from magnitude +4.16 to +4.26<ref name=gcvs/> with a period of 12.57 days.<ref name=Ruban2009/> The star has around 82 times the [[Sun's radius]] and is radiating 767 times the [[Sun's luminosity]] from its enlarged [[photosphere]] at an [[effective temperature]] of {{val|3438|ul=K|fmt=commas}}. {{clear left}} ==References== {{Reflist|refs=
<ref name=Simbad>{{cite simbad | title=2 Cen | access-date=2019-04-06 }}</ref>
<ref name=ayres2024>{{cite journal |last1=Ayres |first1=Thomas |title=In the Trenches of the Solar-Stellar Connection. VII. Wilson-Bappu 2022 |journal=The Astrophysical Journal Supplement Series |date=2023 |volume=266 |issue=1 |page=6 |doi=10.3847/1538-4365/acb535 |doi-access=free |bibcode=2023ApJS..266....6A }}</ref>
<ref name=eggen1992>{{cite journal |last1=Eggen |first1=Olin J. |title=Asymptotic Giant Branch Stars Near the Sun |journal=The Astronomical Journal |date=1992 |volume=104 |page=275 |doi=10.1086/116239 |bibcode=1992AJ....104..275E }}</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=RV>{{cite journal|title=Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system|author=Gontcharov, G. A.|date=2006|journal=Astronomy Letters|volume=32|issue=11|pages=759–771|bibcode=2006AstL...32..759G|doi=10.1134/S1063773706110065|arxiv=1606.08053|s2cid=119231169}}</ref>
<ref name=Cardini2005>{{citation | title=Mg II chromospheric radiative loss rates in cool active and quiet stars | last1=Cardini | first1=D. | postscript=. | journal=Astronomy and Astrophysics | volume=430 | pages=303–311 | date=January 2005 | doi=10.1051/0004-6361:20041440 | bibcode=2005A&A...430..303C |arxiv = astro-ph/0409683 | s2cid=12136256 }}</ref>
<ref name=EgUBV>{{cite journal|author1=Mermilliod, J.-C.|title=Compilation of Eggen's UBV data, transformed to UBV (unpublished)|journal=Catalogue of Eggen's UBV Data|date=1986|bibcode= 1986EgUBV........0M}}</ref>
<ref name="Eggen1998">{{cite journal | title=The HR 1614 Group and HIPPARCOS Astrometry | last1=Eggen | first1=Olin J. | journal=The Astronomical Journal | volume=115 | issue=6 | pages=2453–2458 | date=June 1998 | doi=10.1086/300380 | bibcode=1998AJ....115.2453E | doi-access=free }}</ref>
<ref name=Eggleton2008>{{cite journal | last1=Eggleton | first1=P. P. | last2=Tokovinin | first2=A. A. | title=A catalogue of multiplicity among bright stellar systems | journal=[[Monthly Notices of the Royal Astronomical Society]] | volume=389 | issue=2 | pages=869–879 | date=September 2008 | doi=10.1111/j.1365-2966.2008.13596.x | doi-access=free | bibcode=2008MNRAS.389..869E | arxiv=0806.2878 | s2cid=14878976 }}</ref>
<ref name=Ruban2009>{{cite journal | last1=Ruban | first1=E. V. | last2=Arkharov | first2=A. A. | last3=Hagen-Thorn | first3=E. I. | last4=Novikov | first4=V. V. | title=Physical parameters of the semiregular variable red giant 2 Cen | journal=Astrophysics | volume=52 | issue=3 | pages=383–394 | date=September 2009 | doi=10.1007/s10511-009-9075-3 | bibcode=2009Ap.....52..383R | s2cid=121256121 }}</ref>
<ref name=HD>{{cite journal|bibcode=1999MSS...C05....0H|title=Michigan catalogue of two-dimensional spectral types for the HD Stars, Vol. 5|journal=Michigan Spectral Survey|volume=5|author1=Houk, N.|author2=Swift, C.|year=1999}}</ref>
<ref name="Cousins1951">{{cite journal |last1=Cousins |first1=A. W. J. |title=Photographic magnitudes of the brightest stars |journal=The Observatory |date=October 1951 |volume=71 |pages=201–202 |bibcode=1951Obs....71..201C |url=https://ui.adsabs.harvard.edu/abs/1951Obs....71..201C/abstract |access-date=16 January 2025}}</ref>
<ref name="Kholopov1978">{{cite journal |last1=Kholopov |first1=P. N. |last2=Kukarkina |first2=N. P. |last3=Perova |first3=N. B. |title=63rd Name-List of Variable Stars |journal=Information Bulletin on Variable Stars |bibcode=1978IBVS.1414....1K |date=April 1978 |volume=1414 |pages=1–10 |url=https://ibvs.konkoly.hu/pub/ibvs/1401/1414.pdf |access-date=16 January 2025}}</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 | year=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=67228 Vizier catalog entry ]</ref>
<ref name="Tabur">{{cite journal |last1=Tabur |first1=V. |last2=Bedding |first2=T. R. |last3=Kiss |first3=L. L. |last4=Moon |first4=T. T. |last5=Szeidl |first5=B. |last6=Kjeldsen |first6=H. |title=Long-term photometry and periods for 261 nearby pulsating M giants |journal=Monthly Notices of the Royal Astronomical Society |year=2009 |volume=400 |issue=4 |pages=1945–1961 |doi=10.1111/j.1365-2966.2009.15588.x |bibcode=2009MNRAS.400.1945T |doi-access=free |arxiv=0908.3228 }}</ref>
<ref name=gcvs>{{cite journal|bibcode=2009yCat....102025S|title=VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)|journal=VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S|volume=1|display-authors=etal|last1=Samus|first1=N. N.|last2=Durlevich|first2=O. V.|year=2009}}</ref>
}}
{{Stars of Centaurus}}
[[Category:M-type giants]] [[Category:Asymptotic-giant-branch stars]] [[Category:Semiregular variable stars]] [[Category:Centaurus]] [[Category:Bayer objects|Centauri, g]] [[Category:Durchmusterung objects|CD-33 09358]] [[Category:Flamsteed objects|Centauri, 2]] [[Category:Henry Draper Catalogue objects|120323]] [[Category:Hipparcos objects|067457]] [[Category:Bright Star Catalogue objects|5192]] [[Category:Objects with variable star designations|Centauri, V806]]