An Alpha² Canum Venaticorum star, also known as a spectrum variable, is a type of rotating variable that consists of a main sequence star of spectral type B8p to A7p with a strong magnetic field. Alpha² CVn stars have spectra with abnormally strong lines of silicon, strontium, chromium, and rare earth elements, the intensities of which vary with rotation. They also show magnetic field and brightness changes with periods of 0.5 to 160 days and visual amplitudes of 0.01 to 0.1 magnitude. It is thought the powerful magnetic field of an Alpha² CVn star gives rise to different compositions and brightness at different parts of the stellar surface, in the same way that the Sun's (much weaker) field produces sunspots. The prototype is the companion star of Cor Caroli.