# 2 Centauri

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Star in the constellation Centaurus

This article is about g Centauri; not to be confused with [G Centauri](/source/G_Centauri).

2 Centauri Location of 2 Centauri (circled in red) Observation data Epoch J2000.0 Equinox J2000.0 Constellation Centaurus Right ascension 13h 49m 26.72175s[1] Declination −34° 27′ 02.7929″[1] Apparent magnitude (V) 4.16–4.26[2] Characteristics Evolutionary stage AGB[3] Spectral type M5 III[4] U−B color index +1.44[5] B−V color index +1.49[5] Variable type SRb[2] Astrometry Radial velocity (Rv) +40.7±0.7[6] km/s Proper motion (μ) RA: −41.68±0.23[1] mas/yr Dec.: −59.77±0.18[1] mas/yr Parallax (π) 17.82±0.21 mas[1] Distance 183 ± 2 ly (56.1 ± 0.7 pc) Absolute magnitude (MV) +0.51[7] Details Mass 1.0[8] M☉ Radius 82.4[9] R☉ Luminosity 767[8] L☉ Surface gravity (log g) 0.65[8] cgs Temperature 3,438[8] K Other designations g Centauri, 2 Cen, V806 Cen, CD−33°9358, GC 18666, HD 120323, HIP 67457, HR 5192, SAO 204875[10] Database references SIMBAD data

**2 Centauri** is a single[11] [star](/source/Star) in the [southern](/source/Southern_celestial_hemisphere) [constellation](/source/Constellation) of [Centaurus](/source/Centaurus), located approximately 183 [light-years](/source/Light-year) from [Earth](/source/Earth).[1] It has the [Bayer designation](/source/Bayer_designation) **g Centauri**;[10] *2 Centauri* is the [Flamsteed designation](/source/Flamsteed_designation). This object is visible to the [naked eye](/source/Naked_eye) as faint, red-hued star with an [apparent visual magnitude](/source/Apparent_visual_magnitude) of about 4.2. It is moving away from the Earth with a heliocentric [radial velocity](/source/Radial_velocity) of +41 km/s.[6] The star is a member of the [HR 1614](/source/HR_1614) supercluster.[12]

A [light curve](/source/Light_curve) for V806 Centauri. The main plot shows the long term variability from *[Hipparcos](/source/Hipparcos)* data,[13] and the inset plot shows the variability over the 26.5 day period, using data from Tabur *et al.* (2009).[14] The green curve shows the best-fit sine wave, which has an amplitude of 18 millimagnitudes.

This is an [evolved](/source/Stellar_evolution) [red giant](/source/Red_giant) star with a [stellar classification](/source/Stellar_classification) of M5 III.[4] In 1951, [Alan William James Cousins](/source/Alan_William_James_Cousins) announced that the star, then called g Centauri, is a [variable star](/source/Variable_star).[15] It was given its [variable star designation](/source/Variable_star_designation), V806 Centauri, in 1978.[16] It is classified as a [semiregular](/source/Semiregular_variable_star) [variable star](/source/Variable_star) and its brightness varies from magnitude +4.16 to +4.26[2] with a period of 12.57 days.[17] The star has around 82 times the [Sun's radius](/source/Sun's_radius) and is radiating 767 times the [Sun's luminosity](/source/Sun's_luminosity) from its enlarged [photosphere](/source/Photosphere) at an [effective temperature](/source/Effective_temperature) of 3,438 [K](/source/Kelvin).

## References

1. ^ [***a***](#cite_ref-van_Leeuwen2007_1-0) [***b***](#cite_ref-van_Leeuwen2007_1-1) [***c***](#cite_ref-van_Leeuwen2007_1-2) [***d***](#cite_ref-van_Leeuwen2007_1-3) [***e***](#cite_ref-van_Leeuwen2007_1-4) [***f***](#cite_ref-van_Leeuwen2007_1-5) van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". *Astronomy and Astrophysics*. **474** (2): 653–664. [arXiv](/source/ArXiv_(identifier)):[0708.1752](https://arxiv.org/abs/0708.1752). [Bibcode](/source/Bibcode_(identifier)):[2007A&A...474..653V](https://ui.adsabs.harvard.edu/abs/2007A&A...474..653V). [doi](/source/Doi_(identifier)):[10.1051/0004-6361:20078357](https://doi.org/10.1051%2F0004-6361%3A20078357). [S2CID](/source/S2CID_(identifier)) [18759600](https://api.semanticscholar.org/CorpusID:18759600). [Vizier catalog entry](http://webviz.u-strasbg.fr/viz-bin/VizieR-5?-out.add=.&-source=I/311/hip2&recno=67228)

1. ^ [***a***](#cite_ref-gcvs_2-0) [***b***](#cite_ref-gcvs_2-1) [***c***](#cite_ref-gcvs_2-2) Samus, 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](/source/Bibcode_(identifier)):[2009yCat....102025S](https://ui.adsabs.harvard.edu/abs/2009yCat....102025S).

1. **[^](#cite_ref-eggen1992_3-0)** Eggen, Olin J. (1992). "Asymptotic Giant Branch Stars Near the Sun". *The Astronomical Journal*. **104**: 275. [Bibcode](/source/Bibcode_(identifier)):[1992AJ....104..275E](https://ui.adsabs.harvard.edu/abs/1992AJ....104..275E). [doi](/source/Doi_(identifier)):[10.1086/116239](https://doi.org/10.1086%2F116239).

1. ^ [***a***](#cite_ref-HD_4-0) [***b***](#cite_ref-HD_4-1) Houk, N.; Swift, C. (1999). "Michigan catalogue of two-dimensional spectral types for the HD Stars, Vol. 5". *Michigan Spectral Survey*. **5**. [Bibcode](/source/Bibcode_(identifier)):[1999MSS...C05....0H](https://ui.adsabs.harvard.edu/abs/1999MSS...C05....0H).

1. ^ [***a***](#cite_ref-EgUBV_5-0) [***b***](#cite_ref-EgUBV_5-1) Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". *Catalogue of Eggen's UBV Data*. [Bibcode](/source/Bibcode_(identifier)):[1986EgUBV........0M](https://ui.adsabs.harvard.edu/abs/1986EgUBV........0M).

1. ^ [***a***](#cite_ref-RV_6-0) [***b***](#cite_ref-RV_6-1) Gontcharov, G. A. (2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". *Astronomy Letters*. **32** (11): 759–771. [arXiv](/source/ArXiv_(identifier)):[1606.08053](https://arxiv.org/abs/1606.08053). [Bibcode](/source/Bibcode_(identifier)):[2006AstL...32..759G](https://ui.adsabs.harvard.edu/abs/2006AstL...32..759G). [doi](/source/Doi_(identifier)):[10.1134/S1063773706110065](https://doi.org/10.1134%2FS1063773706110065). [S2CID](/source/S2CID_(identifier)) [119231169](https://api.semanticscholar.org/CorpusID:119231169).

1. **[^](#cite_ref-Cardini2005_7-0)** Cardini, D. (January 2005), "Mg II chromospheric radiative loss rates in cool active and quiet stars", *Astronomy and Astrophysics*, **430**: 303–311, [arXiv](/source/ArXiv_(identifier)):[astro-ph/0409683](https://arxiv.org/abs/astro-ph/0409683), [Bibcode](/source/Bibcode_(identifier)):[2005A&A...430..303C](https://ui.adsabs.harvard.edu/abs/2005A&A...430..303C), [doi](/source/Doi_(identifier)):[10.1051/0004-6361:20041440](https://doi.org/10.1051%2F0004-6361%3A20041440), [S2CID](/source/S2CID_(identifier)) [12136256](https://api.semanticscholar.org/CorpusID:12136256).

1. ^ [***a***](#cite_ref-ayres2024_8-0) [***b***](#cite_ref-ayres2024_8-1) [***c***](#cite_ref-ayres2024_8-2) [***d***](#cite_ref-ayres2024_8-3) Ayres, Thomas (2023). ["In the Trenches of the Solar-Stellar Connection. VII. Wilson-Bappu 2022"](https://doi.org/10.3847%2F1538-4365%2Facb535). *The Astrophysical Journal Supplement Series*. **266** (1): 6. [Bibcode](/source/Bibcode_(identifier)):[2023ApJS..266....6A](https://ui.adsabs.harvard.edu/abs/2023ApJS..266....6A). [doi](/source/Doi_(identifier)):[10.3847/1538-4365/acb535](https://doi.org/10.3847%2F1538-4365%2Facb535).

1. **[^](#cite_ref-9)** Wood, Brian E.; Harper, Graham M.; Müller, Hans-Reinhard (May 2024). ["Resolving Red Giant Winds with the Hubble Space Telescope*"](https://doi.org/10.3847%2F1538-4357%2Fad401f). *The Astrophysical Journal*. **967** (2): 120. [arXiv](/source/ArXiv_(identifier)):[2404.15086](https://arxiv.org/abs/2404.15086). [doi](/source/Doi_(identifier)):[10.3847/1538-4357/ad401f](https://doi.org/10.3847%2F1538-4357%2Fad401f). [ISSN](/source/ISSN_(identifier)) [0004-637X](https://search.worldcat.org/issn/0004-637X).

1. ^ [***a***](#cite_ref-Simbad_10-0) [***b***](#cite_ref-Simbad_10-1) ["2 Cen"](http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=2+Cen). *[SIMBAD](/source/SIMBAD)*. [Centre de données astronomiques de Strasbourg](/source/Centre_de_donn%C3%A9es_astronomiques_de_Strasbourg). Retrieved 2019-04-06.

1. **[^](#cite_ref-Eggleton2008_11-0)** Eggleton, P. P.; Tokovinin, A. A. (September 2008). ["A catalogue of multiplicity among bright stellar systems"](https://doi.org/10.1111%2Fj.1365-2966.2008.13596.x). *[Monthly Notices of the Royal Astronomical Society](/source/Monthly_Notices_of_the_Royal_Astronomical_Society)*. **389** (2): 869–879. [arXiv](/source/ArXiv_(identifier)):[0806.2878](https://arxiv.org/abs/0806.2878). [Bibcode](/source/Bibcode_(identifier)):[2008MNRAS.389..869E](https://ui.adsabs.harvard.edu/abs/2008MNRAS.389..869E). [doi](/source/Doi_(identifier)):[10.1111/j.1365-2966.2008.13596.x](https://doi.org/10.1111%2Fj.1365-2966.2008.13596.x). [S2CID](/source/S2CID_(identifier)) [14878976](https://api.semanticscholar.org/CorpusID:14878976).

1. **[^](#cite_ref-Eggen1998_12-0)** Eggen, Olin J. (June 1998). ["The HR 1614 Group and HIPPARCOS Astrometry"](https://doi.org/10.1086%2F300380). *The Astronomical Journal*. **115** (6): 2453–2458. [Bibcode](/source/Bibcode_(identifier)):[1998AJ....115.2453E](https://ui.adsabs.harvard.edu/abs/1998AJ....115.2453E). [doi](/source/Doi_(identifier)):[10.1086/300380](https://doi.org/10.1086%2F300380).

1. **[^](#cite_ref-HipDataAccess_13-0)** ["Hipparcos Tools Interactive Data Access"](https://www.cosmos.esa.int/web/hipparcos/interactive-data-access). *Hipparcos*. ESA. Retrieved 8 December 2021.

1. **[^](#cite_ref-Tabur_14-0)** Tabur, V.; Bedding, T. R.; Kiss, L. L.; Moon, T. T.; Szeidl, B.; Kjeldsen, H. (2009). ["Long-term photometry and periods for 261 nearby pulsating M giants"](https://doi.org/10.1111%2Fj.1365-2966.2009.15588.x). *Monthly Notices of the Royal Astronomical Society*. **400** (4): 1945–1961. [arXiv](/source/ArXiv_(identifier)):[0908.3228](https://arxiv.org/abs/0908.3228). [Bibcode](/source/Bibcode_(identifier)):[2009MNRAS.400.1945T](https://ui.adsabs.harvard.edu/abs/2009MNRAS.400.1945T). [doi](/source/Doi_(identifier)):[10.1111/j.1365-2966.2009.15588.x](https://doi.org/10.1111%2Fj.1365-2966.2009.15588.x).

1. **[^](#cite_ref-Cousins1951_15-0)** Cousins, A. W. J. (October 1951). ["Photographic magnitudes of the brightest stars"](https://ui.adsabs.harvard.edu/abs/1951Obs....71..201C/abstract). *The Observatory*. **71**: 201–202. [Bibcode](/source/Bibcode_(identifier)):[1951Obs....71..201C](https://ui.adsabs.harvard.edu/abs/1951Obs....71..201C). Retrieved 16 January 2025.

1. **[^](#cite_ref-Kholopov1978_16-0)** Kholopov, P. N.; Kukarkina, N. P.; Perova, N. B. (April 1978). ["63rd Name-List of Variable Stars"](https://ibvs.konkoly.hu/pub/ibvs/1401/1414.pdf) (PDF). *Information Bulletin on Variable Stars*. **1414**: 1–10. [Bibcode](/source/Bibcode_(identifier)):[1978IBVS.1414....1K](https://ui.adsabs.harvard.edu/abs/1978IBVS.1414....1K). Retrieved 16 January 2025.

1. **[^](#cite_ref-Ruban2009_17-0)** Ruban, E. V.; Arkharov, A. A.; Hagen-Thorn, E. I.; Novikov, V. V. (September 2009). "Physical parameters of the semiregular variable red giant 2 Cen". *Astrophysics*. **52** (3): 383–394. [Bibcode](/source/Bibcode_(identifier)):[2009Ap.....52..383R](https://ui.adsabs.harvard.edu/abs/2009Ap.....52..383R). [doi](/source/Doi_(identifier)):[10.1007/s10511-009-9075-3](https://doi.org/10.1007%2Fs10511-009-9075-3). [S2CID](/source/S2CID_(identifier)) [121256121](https://api.semanticscholar.org/CorpusID:121256121).

v t e Constellation of Centaurus List of stars in Centaurus Centaurus in Chinese astronomy Stars Bayer α A (Rigil Kentaurus) B (Toliman) C (Proxima Centauri) β (Hadar) γ δ ε ζ (Leepwal) η θ (Menkent) ι (Kulou) κ λ μ ν (Heng) ξ1 ξ2 ο1 ο2 π ρ σ τ υ1 υ2 φ χ ψ x1 x2 C3 D E F G H J K M N Q Flamsteed 1 (i) 2 (g) 3 (k) 4 (h) Variable R T V Y RR SV SX BV DY UY V346 V553 V744 V752 V761 (a) V763 (C1) V766 V779 (Krzemiński's star) V803 V810 V816 (Przybylski's Star) V831 V842 V885 V886 V863 V1032 V1369 V1400 V1935 HR 4460 (A) 4466 (C2) 4499 4522 4523 4537 (j) 4546 (B) 4721 4748 (u) 4796 4817 (l) 4831 (w) 4874 (p) 4888 (e) 4889 (n) 4940 (f) 4979 4989 5006 (r) 5041 (m) 5089 (d) 5174 (z) 5222 (y) 5224 5241 5297 5358 (v) 5371 5471 (b) 5485 (c1) 5489 (c2) HD 97413 98176 100453 101581 101930 102117 (Uklun) 103197 107914 108236 109749 110113 113538 113766 114386 114729 115600 116434 (Matza) 117207 117618 (Dofida) 117939 120411 121228 121504 124448 (Popper's Star) 125072 125595 131399 Other 2MASS J1126−5003 2M1207 Gaia BH2 HD 131399 Ab PSR B1259−63 PSR J1311−3430 TOI-763 WASP-15 (Nyamien) WASP-41 WASP-42 WASP-167/KELT-13 Exoplanets 2M1207b b Centauri b HD 101930 b HD 102117 b (Leklsullun) HD 103197 b HD 109749 b HD 113538 b c HD 114386 b HD 114729 b HD 117207 b HD 117618 b (Noifasui) HD 121504 b HIP 65426 b (Najsakopajk) HIP 67522 b NGTS-13b Proxima Centauri b c d WASP-15b (Asye) Star clusters NGC 3766 4230 4507 5281 5286 5316 5460 5617 5662 Other IC 2944 ω Centauri Scorpius–Centaurus association Stock 16 Nebulae NGC 3918 5307 Other Boomerang Nebula Fleming 1 G292.0+1.8 G306.3-0.9 Gum 41 IC 2944 IRAS 13208−6020 RCW 79 RCW 86 Southern Crab Nebula SuWt 2 Galaxies NGC 3557 3568 3749 3783 4444 4603 4622 4650A 4683 4696 4706 4709 4729 4730 4743 4744 4909 4930 4945 4976 5011 A 5026 5064 5082 5090 5091 5102 5114 5121 5128 (Centaurus A) 5161 5206 5253 5266 5291 5398 5408 5419 5483 5516 Other ESO 269-57 ESO 325-4 ESO 383-76 ESO 444-46 Fourcade-Figueroa Object IC 3370 IC 4214 IC 4329A IRAS 13224−3809 J1144−4308 LEDA 677373 PKS 1144−379 PKS 1353−341 PKS 1424−418 Galaxy clusters Abell S740 Centaurus Cluster Shapley Supercluster Astronomical events GW190521 SN 185 SN 1895B (Z) SN 1972E SN 1986G J1407b SN 2019so Category

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Adapted from the Wikipedia article [2 Centauri](https://en.wikipedia.org/wiki/2_Centauri) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/2_Centauri?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.