Variations in the phase lag between radial-velocity and light curves of the beta CMa stars.

By analysing the existing photometric and spectroscopic data for the best observed β CMa stars, together with that from new observations, the author shows that a secular variation exists in the phase lag between the light and velocity curves. The phase lag of at least three stars (δ Cet, BW Vul and β Cep) have sinusoidal variations with semiamplitude of 0.1 period about the standard 0.25 value. These phase lag variations may be attributed to physical variations in the non adiabatic outer zone of the stars.