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

Abstract

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 theγDor-type oscillations. The existence of these hot objects needs an explanation. Therefore, we selected, observed and studied 24 hotγDor and hybrid candidates to investigate their properties. The atmospheric parameters, chemical abundances and vsini values of the candidates were obtained using medium-resolution (R= 46 000)spectra taken with the FIES instrument mounted at the NordicOptical Telescope. We also carried out frequency analyses of theKeplerlong- and short-cadence data to determine the exact pulsation contents. We found only five bona-fide hotγDor and three bona-fide hot hybrid stars in our sample. The other 16 stars were found to benormalγDor,δSct, or hybrid variables. No chemical peculiarity was detected in the spectra of the bona-fide hotγDor and hybrid stars. We investigated the interplay between rotation and pulsational modes. We also found that the hotγDor stars havehigherGaialuminosities and larger radii compared to main-sequence A-F stars.

Accepted for publication in Monthly Notices of the Royal Astronomical Society Letters

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• Overstable Convective Modes in Rotating Early Type Stars
• A tidally tilted sectoral dipole pulsation mode in the eclipsing binary TIC 63328020
• High-Amplitude gamma Doradus Variables
• Rotational modulation in A and F stars: Magnetic stellar spots or convective core rotation?
• Unresolved Rossby and gravity modes in 214 A and F stars showing rotational modulation
• HD 42477: coupled r modes, g modes and a p mode in an A0Vnne star
• Non-linear excitation of low frequency modes by overstable convective modes in rotating stars