be driven by the $\kappa$-mechanism operating in the Z-bump despite low metallicity. The opposite situation occurs for models with higher metallicities. For example with $Z=0.02$ there is a large instability area beyond MS but there are no unstable modes in the blue loop models, because of too low temperature the blue loops reach. The exceptions are the highest considered masses - $M\approx 18 M_\odot$ for OPAL opacities and $M\approx 16 - 18 M_\odot$ for OP opacity tables. For those masses there are a few models on the hottest part of the blue loops that have unstable modes.

For every calculated mass and independently of metallicity or opacity tables we obtained unstable radial modes in the cooler models on the red giant branch or its vicinity. This result is similar to the one from Saio et al. (2013) and it was expected because in this area of HR diagram a classical instability strip is located. Those models are high-mass classical cepheids, in which the pulsations are driven in a region of the second ionization of helium. It is important to note that there are two effects that make the pulsational code we use unsuitable for such stars: the linear approximation and 