Über die Stabilität der Radialen Pulsation der Sterne

Abstract

The one zone model which was introduced by BAKER for physical interpretation of the excitation of stellar pulsation is generalized in the following two developments.

1) By use of the quasi-adiabatic approximation the contribution of a radiative layer to the stability is formulated. Besides BAKER’s terms, a contribution arises from the variation of the adiabatic temperature gradient, but its net effect may not be as important as BAKER’s term, if it is integrated throughout the star. Accordingly, BAKER’s conclusion is qualitatively justified.

2) The one zone model in which the energy is transported partly by convection is investigated. The characteristic time of convection is assumed to be much shorter than the period of pulsation. The stability criterion agrees with the one given by BAKER showing destabilizing effect in ionization zones of abundant elements, if the convective heat transport is negligible compared with the radiative transport. In the opposite case, the criterion depends only on the thermodynamic quantities of gas, in such a way that the ionization zones tend to excite the pulsation.

It is concluded, therefore, that the coincidence of the ionization zones of abundant elements with zones which store pulsational energy is generally favorable for the maintenance of the radial pulsation of a star.