The high amplitude delta Scuti stars seem to be a rather inhomogeneous group of variable stars consisting of both population I and II stars. Although most of them tends to pulsate in a single radial mode, some of them pulsate in double mode. Only a few non-radial mode were reported in high amplitude delta Scuti stars. The colour amplitude ratios and phase shifts are well-known discriminators between the radial and non-radial modes (if high precision and long enough colour data are used). However, these values can serve as discriminator for the overtones, too. Grouping of the excited modes with the same quantum numbers could be expected. The colour amplitude ratios and phase shifts of high amplitude delta Scuti stars, based on a published homogeneous set of high precision Stromgren photometry, are investigated for correlation between the distinct branches of this inhomogeneous group of pulsating variable stars.
IAU Joint Discussion
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