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Nonradial oscillations in classical pulsators. Prospects for seismology.
Wojtek Dziembowski (Copernicus Astronomical Center, Polish Academy of Sciences), R. Smolec (Nicolaus Copernicus Astronomical Center)
We have now a good evidence that nonradial modes of moderate degrees (l=7-9) are excited in a large number of 1O Cepheids and RR Lyrae (RRc) stars. The first detected signature of the presence of these modes was the periodicity at (0.6-0.65)P_1O, which is due to harmonics that are associated with spherically symmetric changes of radiative flux. Only recently, thanks to precise space-based observations and extensive ground-based OGLE photometry, the signal at mode frequencies has been detected. The excited modes are very well trapped in stellar envelopes and very similar in terms of driving properties to the first two radial modes. It is unlikely that they play any essential role in the development of pulsation. Rather, they are passive contaminants useful as a source of new constraints on star parameters.