On possible explanations of pulsations in Maia stars
Jadwiga Daszynska-Daszkiewicz (Uniwersytet Wroclawski), Przemyslaw Walczak (Uniwersytet Wroclawski), Alosha Pamyatnykh (Copernicus Astronomical Center, Warsaw)

The long-time photometric surveys in a few young open clusters allowed to identify the light variability in stars located between the well defined δ Scuti variables and Slowly Pulsating B-type stars (Mowlavi et al, 2013, 2015). The period of these changes is in the range of about 0.1 - 0.7 [d] corresponding to the frequencies of about 1.4 - 10 [d^-1]. Several objects of this type were suggested also from the analysis of the Kepler data (Balona et al. 2015). Assuming the pulsational origin of this variability, we test the two hypotheses. The first and the old one involves the very high rotation which, both, enhances the pulsational instability and causes the shift of unstable modes to the higher frequency range. We perform the pulsational computations in the framework of the traditional approximation and compare them with the results from the literature. In the second and the new scenario, we modify the opacity profile in order to excited pulsational modes in the required frequency range. We show that by increasing opacity at certain depths (log T) and considering modes with the harmonic degree up to 6, it is also possible to get the pulsational instability. This scenario works for, both, slow and fast rotating stars of B8-A2 type.