Theoretical predictions on Type II Cepheids

A new theoretical prediction for the instability strip boundaries of these classes of variable stars has been obtained together with their dependence on metal abundance. The predicted light and radial-velocity curves were computed along the evolution inside the strip, showing how the amplitude and the morphology are affected by the position relative to the edges and by the luminosity and mass values. The transformation of bolometric light curves into various photometric systems allowed us to provide new theoretical period-luminosity and period-Wesenheit relations for BL Her and W Vir.

These relations are found to be consistent with previously published RR Lyrae model results but with a smaller metallicity dependence. Moreover, the application of the inferred theoretical relations to Magellanic and Galactic Type II Cepheid data provides results in good agreement with some independent distance estimates in the literature.