A type of main-sequence, extrinsic variable star; abbr. ACV. Stellar rotation produces brightness variations of 0.01–0.1 mag., accompanied by changes in the strengths of the spectral lines and the magnetic fields. The rotational periods range from 0.5 days to more than 160 days. The spectra (B8p–A7p) exhibit abnormally strong lines of silicon, strontium, chromium, and rare-earth elements. Stars in the ACVO subtype undergo non-radial pulsation (periods 0.004–0.01 days), with small (0.01-mag.) variations superimposed on the fluctuations caused by the rotation. Alpha2 CVn itself, better known as Cor Caroli, is an A0 dwarf with strong spectral lines of silicon and europium, varying between magnitudes 2.84 and 2.98 every 5.47 days.