Date of this Version
THE ASTROPHYSICAL JOURNAL, Vol. 157, August 1969.
Nuclear energy of the stellar core is found to be the direct source of energy fed into radial pulsations in two classes of blue variable stars. The μ-mechanism (reversal of the gradient of mean molecular weight, which reduces the central condensation) or the β-mechanism (high radiation pressure) can explain the basic variability of β Cephei stars if they are burning hydrogen in their cores, have accreted a helium-rich envelope, and are the luminous secondaries of close binary systems. If the composition reversal does not lead to significant mixing in the envelope, the μ-mechanism will operate in inhomogeneous stars of 6-95 M ʘ. If rapid mixing takes place, the β-mechanism will operate in completely homogeneous stars of 12-60 M ʘ. The β-mechanism can also explain the variability of many Wolf-Rayet stars if they are burning helium in their cores, have masses in excess of ~8 M ʘ with a thin or absent hydrogen envelope, and are the luminous primaries of close binary systems.