Spectroscopy of hot gamma Doradus and A-F hybrid Kepler candidates close to the hot border of the delta Scuti instability strip

If gamma Dor-type pulsations are driven by the convective blocking mechanism, a convective envelope at a sufficient depth is essential. There are several hot gamma Dor and hybrid star candidates in which there should not be an adequate convective envelope to excite the gamma Dor-type oscillations. The existence of these hot objects needs an explanation. Therefore, we selected, observed, and studied 24 hot gamma Dor and hybrid candidates to investigate their properties. The atmospheric parameters, chemical abundances, and vsin i values of the candidates were obtained using medium-resolution (R = 46 000) spectra taken with the Fibre-fed Echelle Spectrograph instrument mounted at the Nordic Optical Telescope. We also carried out frequency analyses of the Kepler long- and short-cadence data to determine the exact pulsation contents. We found only five bona fide hot gamma Dor and three bona fide hot hybrid stars in our sample. The other 16 stars were found to be normal gamma Dor, delta Sct, or hybrid variables. No chemical peculiarity was detected in the spectra of the bona fide hot gamma Dor and hybrid stars. We investigated the interplay between rotation and pulsational modes. We also found that the hot gamma Dor stars have higher Gaia luminosities and larger radii compared to main-sequence A-F stars.