R Centauri (R Cen) is aMira variable star in theconstellationCentaurus. When it is near its maximum brightness, it is faintly visible to thenaked eye under very good observing conditions.
The distance to R Centauri as indicated by itsGaia Data Release 3parallax is about 2,900 light years, but that is considered to be potentially unreliable.[2] TheGaia Data Release 2 parallax was negative and relatively meaningless.[10] The olderHipparcos parallax suggested a distance of about 1,300 light years, but with a wide margin of error.[11] Estimates based on an assumed brightness for the star, adjusted forextinction, give distances as low as 750 light years.[12]
Theeffective temperature of R Centauri'sphotosphere has been calculated by different methods to be2,403 K[9] or3,450 K.[5] Its luminosity is even more uncertain, depending on assumptions about the distance. At a distance of384 pc, thebolometric luminosity would be 11,342 L☉,[9] while assuming a larger distance of640 pc the luminosity would be over 47,000 L☉.[5] In either case, it is a very large star, over 600 R☉.[9]
Benjamin Apthorp Gould discovered R Centauri, in 1871.[13] The star is a Mira variable and its brightness varies frommagnitude +5.2 to +11.5 with a period of about 500 days. It used to have an unusual double-peakedlight curve, but by 2001 this had reverted to an almost normal single-peaked curve. Prior to 1950 the period was about 550 days, but since then has decreased to about 500 days. A 2016 analysis ofASAS data derived a period of 498.84 days.[14]
It is thought that the unusual behaviour of R Centauri is caused by aflash in the helium shell around its core, which occurs periodically inasymptotic giant branch (AGB) stars as the mass of the helium shell increases with helium from the outer hydrogen shell.[4] It is also an H2Omaser source.[15]
^abcSamus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)".VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S.1.Bibcode:2009yCat....102025S.
^Wilson, R.E (1953). "General Catalogue of Stellar Radial Velocities".Carnegie Institute Washington D.C. Publication. Washington: Carnegie Institution of Washington.Bibcode:1953GCRV..C......0W.
^Celis, L. (1995). "Luminosity Attenuation and Distances of Red Giant Stars".The Astrophysical Journal Supplement Series.98: 701.Bibcode:1995ApJS...98..701C.doi:10.1086/192175.
^Lepine, J.R.D.; Paes de Barros, M.H. (1977). "Characteristics of the H2O emission from Mira variables".Astronomy and Astrophysics.56:219–226.Bibcode:1977A&A....56..219L.
