Alpha2 Canum Venaticorum variable

Short description: Variable star type

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

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

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(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

1. ↑ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html.
2. ↑ 2.0 2.1 2.2 2.3 Faltová, N. et al. (December 2021), "A case study of ACV variables discovered in the Zwicky Transient Facility survey", Astronomy & Astrophysics 656: id. A125, doi:10.1051/0004-6361/202141534, Bibcode: 2021A&A...656A.125F.
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 , 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, doi:10.1134/S1063772917010085, Bibcode: 2017ARep...61...80S.

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Variable stars

Pulsating|

| Cepheids and
cepheid-like|

* Classical
* Type II (BL Herculis, W Virginis, RV Tauri)
* RR Lyrae
* Delta Scuti
* Rapidly oscillating Ap
* SX Phoenicis

|

Blue-white with
early spectra|

* Alpha Cygni
* Beta Cephei
* Slowly pulsating B-type
* PV Telescopii
* Blue large-amplitude pulsator

Long-period|

* Mira
* Semiregular
* Slow irregular

Other|

* Gamma Doradus
* Solar-like oscillations
* White dwarf

Eruptive|

| Protostar and PMS|

* Herbig Ae/Be
* Orion
* FU Orionis
* T Tauri

|

Giants and
supergiants|

* Luminous blue variable
* R Coronae Borealis (DY Persei)
* Yellow hypergiant

Eruptive binary|

* Double periodic
* FS Canis Majoris
* RS Canum Venaticorum

Other|

* Flare
* Gamma Cassiopeiae
* Lambda Eridani
* Wolf–Rayet

Cataclysmic|

* AM Canum Venaticorum
* Dwarf nova
* Luminous red nova
* Nova
* Polar
* Intermediate polar
* Supernova
* Hypernova
* SW Sextantis
* Symbiotic
* Symbiotic nova
* Z Andromedae

Rotating|

| Non-spherical|

* Rotating ellipsoidal

|

Stellar spots|

* BY Draconis
* FK Comae Berenices

Magnetic fields|

* Alpha² Canum Venaticorum
* Pulsar
* SX Arietis

Eclipsing|

* Algol
* Beta Lyrae
* Planetary transit
* W Ursae Majoris

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