Alpha2 Canum Venaticorum variable

Lore & Background

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. This is now the prototype of the α2 CVn class of variables.

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. 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. 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.

Reader's Guide

The α2 CVn variables represent a class of magnetic chemically peculiar stars whose variability arises from an inhomogeneous distribution of elements on their surfaces, modulated by rotation. Their study provides insight into the interplay between magnetic fields, stellar rotation, and atmospheric chemistry in upper main sequence stars. The oblique rotator model, which explains how surface spots are carried across the field of view, is central to understanding these stars. The class is named after its prototype, α2 Canum Venaticorum, whose 5.47-day brightness cycle of 0.14 magnitudes was the first such variation observed. These stars are notable for their strong magnetic fields and enhanced spectral lines of silicon, strontium, or chromium. Their brightness variations, typically 0.01 to 0.1 magnitudes over periods from half a day to 160 days, are accompanied by changes in spectral line profiles and magnetic field strength, all with the same period. The spots are thought to result from a combination of factors including a weak stellar wind, magnetic field properties, a weak convection zone, and slow rotation. Naked-eye examples of this class are listed for stars with typical brightness magnitude 6.5 or brighter.

Did You Know?

• These stars are of spectral class B8p to A7p with strong magnetic fields.
• Their brightness variations typically range from 0.01 to 0.1 magnitudes over 0.5 to 160 days.
• The variations are believed to equal the star's rotation period.