Metallicity of clusters from RRab pulsators: results of an automatic analysis

The stability of massive stars is re-examined with respect to an adiabatic dynamical instability discovered by Stothers & Chin. An adiabatic stability analysis is performed, its validity for the objects being considered is discussed, and the relation between the mean adiabatic index and adiabatic stability is commented on. As the results of Stothers & Chin could not be confirmed, we suspect that luminous blue variable instability is due to non-adiabatic effects.