Hybrid γdORADUS-δScuti Pulsators: New insights into the physics of the oscillations from kepler observations

Observations of the pulsations of stars can be used to infer their interior structure and test theoretical models. The main-sequence γDoradus (Dor) and δScuti (Sct) stars with masses 1.2-2.5M are particularly useful for these studies. The γDor stars pulsate in high-order g-modes with periods of order 1day, driven by convective blocking at the base of their envelope convection zone. The δSct stars pulsate in low-order g- and p-modes with periods of order 2 hr, driven by the κ mechanism operating in the He II ionization zone. Theory predicts an overlap region in the Hertzsprung-Russell diagram between instability regions, where "hybrid" stars pulsating in both types of modes should exist. The two types of modes with properties governed by different portions of the stellar interior provide complementary model constraints. Among the known γDor and δSct stars, only four have been confirmed as hybrids. Now, analysis of combined Quarter 0 and Quarter 1 Kepler data for hundreds of variable stars shows that the frequency spectra are so rich that there are practically no pure δSct or γDor pulsators, i.e., essentially all of the stars show frequencies in both the δSct and the γDor frequency range. A new observational classification scheme is proposed that takes into account the amplitude as well as the frequency and is applied to categorize 234 stars as δSct, γDor, δSct/γDor or γDor/δSct hybrids. © 2010. The American Astronomical Society. All rights reserved.