The γ Doradus CoRoT target HD 49434 -: I.: Results from the ground-based campaign

Context. We present an extensive ground-based photometric and spectroscopic campaign of the gamma Dor CoRoT target HD 49434. This campaign was a preparatory step of the CoRoT satellite observations, which occurred between October 2007 and March 2008. Aims. With satellite data, detection of low-degree pulsation modes only is achievable, and, as no filters are available, with poor identification. Ground-based data promise eventually to identify additional modes and provide extra input for the identification: spectroscopic data allows the detection of high-degree modes and an estimate of the azimuthal number m. We attempt to detect and identify as many pulsation modes as possible from the ground-based dataset of the gamma Dor star HD 49434, and anticipate the CoRoT results. Methods. We searched for frequencies in the multi-colour variations, the pixel-to-pixel variations across the line profiles, and the moments variations in a large dataset, consisting of both multi-colour photometric and spectroscopic data from different observatories, using different frequency analysis methods. We performed a tentative mode identification of the spectroscopic frequencies using the Moment Method and the Intensity Period Search Method. We also completed an abundance analysis. Results. The frequency analysis clearly indicates the presence of four frequencies in the 0.2-1.7 d(-1) interval, as well as six frequencies in the 5-12 d(-1) domain. The low frequencies are typical of gamma Dor variables, while the high frequencies are common to delta Sct pulsators. We propose that the frequency 2.666 d(-1) is the rotational frequency. All modes, for which an identification was possible, appear to be high-degree modes (3 <= l <= 8). We did not find evidence for a possible binary nature of the star HD 49434. The element abundances that we derived are consistent with values obtained in previous analyses. Conclusions. We classify the gamma Dor star HD 49434 as a hybrid pulsator, which pulsates simultaneously in p-and g-modes. This implies that HD 49434 is an extremely interesting target for asteroseismic modelling.