Abstract

The majority of intermediate mass and massive main sequence stars rotate rapidly. This affects their structure, evolution, lifetime, chemical yields, and final outcome. Modelling such stars is highly challenging due to the departure from spherical symmetry and is subject to many uncertainties. Hence, it is necessary to constrain these stars observationally in order to progress in our understanding of them. Asteroseismology, the study of stellar pulsations, is currently the only approach we have at our disposal for probing their internal structure, and is accordingly a particularly important source of information. However, as will be described in this seminar, it is necessary to overcome a number of hurdles to carry out asteroseismic investigations of such stars.

First of all, pulsation calculations must be carried out in a 2D context in order to fully include the effects of rotation. The geometry of the resultant pulsation modes can differ substantially from that of their non-rotating counterparts thus leading to a different mode classification. Likewise, the associated pulsation frequency spectra follow new patterns which are more complicated than in the non-rotating case. This leads to the next major hurdle which intervenes when trying to interpret observed pulsation spectra, namely mode identification, i.e. correctly matching theoretical modes with observed pulsation frequencies. Indeed, direct comparisons between the two typically yield multiple solutions due to the high density of theoretical frequencies compared with the observed ones. Therefore, current strategies for interpreting observed pulsations involve looking for specific frequency spacings, such as the large frequency separation and the rotation rate, and/or applying mode identification techniques based on multicolour photometric observations and spectroscopic observations of line profile variations, both of which need to be adapted to the rapidly rotating case. These interpretation strategies will be illustrated through various recent studies of observed stars.