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Alpha2 Canum Venaticorum variable

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A light curve for α2 Canum Venaticorum, plotted from TESS data[1]

Alpha2 Canum Venaticorum variable (or α2 CVn variable) is a type of magnetic variable star.[2] These are chemically peculiar stars of the CP2 type that are photometrically variable. That is, they are upper main sequence stars of spectral class B8p to A7p, with strong magnetic fields and strong silicon, strontium, or chromium spectral lines. Their brightness typically varies by 0.01 to 0.1 magnitudes over the course of 0.5 to 160 days.[3]

The first CP2 variable to be discovered was α2 Canum Venaticorum, a star in the binary system of Cor Caroli, which lies in the northern constellation of Canes Venatici. Its brightness fluctuates by 0.14 magnitudes with a period of 5.47 days.[4] This is now the prototype of the α2 CVn class of variables.[2]

In addition to their brightness, the intensities and profiles of the spectral lines of α2 CVn variables vary, as do their magnetic fields. The periods of these variations are all equal and are believed to equal the period of rotation of the star. It is thought that they are caused by an inhomogeneous distribution of chemical elements in the atmospheres of these stars.[5] These result in spots and enhanced element abundances, which produce localized variations in surface flux. The oblique rotator model explains how these variations are carried across the field of view, resulting in the stellar variability.[2] Several factors are thought responsible for the spots, including a weak stellar wind, the properties of the magnetic field, a weak convection zone, and a slow rotation rate.[2]

Naked eye examples

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This list shows selected variables of this class that are visible to the naked eye. That is, their typical brightness is magnitude 6.5 or brighter.

List of Alpha2 Canum Venaticorum Variables[6]
Designation (name) Constellation Discovery Apparent magnitude (Maximum) Apparent magnitude (Minimum) Range of magnitude Spectral type Comment
(α2 Canum Venaticorum) Cor Caroli Canes Venatici   2.84 2.98 0.14 A0Vp(Si-Cr-Eu) Prototype
(ε UMa) Alioth Ursa Major 1.76 0.02 A1III-IVp kB9(Cr-Eu) Brightest member
α Dor Dorado 3.26 3.30 0.04 B9IIIp(Si) One of the hottest; binary
α Psc (Alrescha) Pisces 3.82 3.83 0.01 A2IVp(Sr) Binary
β Hydrae A Hydra 1834 4.67 4.71 0.04 B8.5IIIp(Si) Hottest member; binary
HD 187474 Sagittarius 5.28 5.34 0.06 A0 EuCrSr Long 6.4 year period; binary

References

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  1. ^ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 8 December 2021.
  2. ^ a b c d Faltová, N.; et al. (December 2021), "A case study of ACV variables discovered in the Zwicky Transient Facility survey", Astronomy & Astrophysics, 656, id. A125, arXiv:2108.11411, Bibcode:2021A&A...656A.125F, doi:10.1051/0004-6361/202141534.
  3. ^ Variability types, General Catalogue of Variable Stars, Sternberg Astronomical Institute, Moscow, Russia. Accessed on line August 20, 2008.
  4. ^ alf 2 CVn , database entry, General Catalogue of Variable Stars Archived 2017-06-20 at the Wayback Machine, Sternberg Astronomical Institute, Moscow, Russia. Accessed on line August 20, 2008.
  5. ^ pp. 83–85, Variable Stars, Michel Petit, foreword by Paolo Maffei, tr. from French by W. J. Duffin, Chichester, UK: John Wiley & Sons, 1987, ISBN 0-471-90920-3.
  6. ^ Samus', N. N.; et al. (2017), "General catalogue of variable stars: Version GCVS 5.1", Astronomy Reports, 61 (1): 80–88, Bibcode:2017ARep...61...80S, doi:10.1134/S1063772917010085, S2CID 125853869.
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