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Hybrid stars like Nu Eridani and 12 Lacertae show two different types ofpulsations: (i) low-order acoustic and gravity modes of the Beta Cephei typewith periods of about 3-6 hours, and (ii) high-order gravity modes of the SPBtype with periods of about 1.5-3 days. Theoretical computations using both OPALand OP opacity data well reproduce short period low-order pulsations of theBeta Cep type and show a tendency to instability of high-order gravity modes,especially for stellar models built with the OP opacities. However, instabilityat observed long periods has not been achieved. We test effects of artificialopacity modifications in the deep envelope on the instability of some hybridstar models. For Nu Eri models, an opacity increase both in the Z opacity bumpregion at temperature of about 200 000 K and in the region of the deeperopacity bump at temperature of about 2-2.5 million degrees (this bump is alsomainly due to excited ions of the iron-group elements) may result ininstability of the high-order gravity modes with the observed periods. Theshortest observed period of 3 hours can also be excited in modified models.However, the required opacity increase seems to be quite large (up to 2 timesin some stellar layers) which may be incompatible with atomic physics.

Can opacity changes help to reproduce the hybrid star pulsations?