As the interior of stars is not directly observable, accurate information is gathered from stellar oscillations which penetrate deep inside the star and whose behaviour is uniquely determined by the properties of the overall stellar structure. For an aster oseismic study it is important to unravel and interpret accurately the pulsational frequency spectra of stars. Promising targets are non-radially pulsating stars that oscillate with many modes. Ground-based multi-colour photometry and high-resolution spectroscopy can capture the periodic temperature, light and radial velocity variations accurately and allow a careful study of the pulsational behaviour of stars and an identification of pulsation modes. However, one of the limiting factors of ground-based ob servations is the restricted time window. Observations in space can overcome this problem. The future (2006) space mission COROT, dedicated to stellar seismology and the search for extra-solar planets, will allow a high photometric precision and a continuous monitoring of targets without time-gap. As targets will be chosen among different types of pulsators along the main-sequence, COROT will offer an excellent opportunity to improve the understanding of the evolution of stars with different masses. In this context we propose a ground-based study, both photometric and spectroscopic, of potential primary and secondary targets (in particular delta Sct and gamma Dor stars) of the COROT space mission, in order to characterise the targets and optimise the COROT scientific prospects. Additionally, we propose a dedicated spectroscopic study of the class of gamma Dor stars, whose high-order g-mode pulsational behaviour is not well understood yet, with the aim to constrain their pulsational characteristics and to understand their link between p-modes and solar-like pulsators. This information is of utmost importance for future seismic modelling.
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