Detection of a large sample of γ Doradus stars from Kepler space photometry and high-resolution ground-based spectroscopy

Context. The launches of the MOST, CoRoT, and Kepler missions opened up a new era in asteroseismology, the study of stellar interiors via interpretation of pulsation patterns observed at the surfaces of large groups of stars. These space missions deliver a huge amount of high-quality photometric data suitable to study numerous pulsating stars. Aims. Our ultimate goal is a detection and analysis of an extended sample of. Dor-type pulsating stars with the aim to search for observational evidence of non-uniform period spacings and rotational splittings of gravity modes in main-sequence stars typically twice as massive as the Sun. This kind of diagnostic can be used to deduce the internal rotation law and to estimate the amount of rotational mixing in the near core regions. Methods. We applied an automated supervised photometric classification method to select a sample of 69 Gamma Doradus (gamma Dor) candidate stars. We used an advanced method to extract the Kepler light curves from the pixel data information using custom masks. For 36 of the stars, we obtained high-resolution spectroscopy with the HERMES spectrograph installed at the Mercator telescope. The spectroscopic data are analysed to determine the fundamental parameters like T-eff, logg, v sin i, and [M/H]. Results. We find that all stars for which spectroscopic estimates of Teff and log g are available fall into the region of the HR diagram, where the. Dor and delta Sct instability strips overlap. The stars cluster in a 700 K window in effective temperature; log g measurements suggest luminosity class IV-V, i.e. sub-giant or main-sequence stars. From the Kepler photometry, we identify 45 gamma Dor-type pulsators, 14 gamma Dor/delta Sct hybrids, and 10 stars, which are classified as possibly gamma Dor/delta Sct hybrid pulsators. We find a clear correlation between the spectroscopically derived v sin i and the frequencies of independent pulsation modes. Conclusions. We have shown that our photometric classification based on the light curve morphology and colour information is very robust. The results of spectroscopic classification perfectly agree with the photometric classification. We show that the detected correlation between v sin i and frequencies has nothing to do with rotational modulation of the stars but is related to their stellar pulsations. Our sample and frequency determinations offer a good starting point for seismic modelling of slow to moderately rotating gamma Dor stars.