The pulsational behaviour of variable stars in the lower part of the instability strip

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The lower part of the classical instability strip and the surrounding main sequence are populated by a large variety of pulsating variable stars. In the past years a great effort was made by the stellar group of Brera Observatory to collect a large amount of photometric and spectroscopic data on Delta Sct stars, the more numerous class. In this paper I will describe our approach to this study. In Sect. 2.1 I show as the light curves of high-amplitude Delta Sct stars can be described in a synthetic and powerful way by using the Fourier decomposition. In Sect. 2.2 some interesting cases are presented, i.e. the peculiar light curves of some double-mode pulsators and the multiperiodicity of V974 Oph. As regards the small amplitude Delta Sct stars, the results which can be extracted from the photometry and (high-resolution) spectroscopy are discussed in Sect. 3; the importance of combining the two techniques into the synergic approach is stressed. As a final step, an excursus on the Gamma Dor stars is presented in Sect.4; the rich pulsational content makes these stars very similar to Delta Sct variables.