Opacity and nonlinear effects on theoretical BL Herculis models

Abstract

Carson et al. (1981) have discussed the low-mass BL Herculis variables mainly on the basis of nonlinear pulsation theory, while King et al. (1981) have concentrated on the linear theory. The nonlinear results provide light and velocity curve bumps which have been interpreted as an indication of a near resonance of the radial second overtone period (Pi(2)) with the radial fundamental mode period (Pi(0)). There is a discrepancy between the results obtained in both considered investigations. This discrepancy might be due to differences in the opacities used in both studies, or it may be caused by ifferences in the modeling approach. The present study is concerned with an investigation of these two possible causes of the discrepancy. It is found that there are slight differences in the resonance when using the two different opacity tables. However, the major effect is that Pi(2)/Pi(0)=0.5 occurs at the lower (observed) period for nonlinear calculations at 0.55 solar mass, but not for the linear results.