Attention is drawn to a group of stars of luminosity class Ia, in which variation of radial velocity has long been known in semi-regular cycles of 5 to 30 days. The interval of approximate repetition appears to be positively correlated with the luminosity of the star.

Recent spectrophotometry of the absorption lines, especially by Rosendhal, Aydin, Groth, and Buscombe shows a considerable variation in the strength of Balmer lines (with emission components detected at H∝), as well as those of metallic ions. The microturbulence parameter derived from curves of growth for Fe ii varies by a factor of two or more during some cycles.