By using a non-local and time-dependent convection theory , we have calculated radial and low-degree non-radial oscillations for stellar evolutionary models with M = 1.4 –3.0 \mathrm { M } _ { \odot } .
The results of our study predict theoretical instability strips for \delta Scuti and \gamma Doradus stars , which overlap with each other .
The strip of \gamma Doradus is slightly redder in colour than that of \delta Scuti .
We have paid great attention to the excitation and stabilization mechanisms for these two types of oscillations , and we conclude that radiative \kappa mechanism plays a major role in the excitation of warm \delta Scuti and \gamma Doradus stars , while the coupling between convection and oscillations is responsible for excitation and stabilization in cool stars .
Generally speaking , turbulent pressure is an excitation of oscillations , especially in cool \delta Scuti and \gamma Doradus stars and all cool Cepheid- and Mira-like stars .
Turbulent thermal convection , on the other hand , is a damping mechanism against oscillations that actually plays the major role in giving rise to the red edge of the instability strip .
Our study shows that oscillations of \delta Scuti and \gamma Doradus stars are both due to the combination of \kappa mechanism and the coupling between convection and oscillations , and they belong to the same class of variables at the low-luminosity part of the Cepheid instability strip .
Within the \delta Scuti– \gamma Doradus instability strip , most of the pulsating variables are very likely hybrids that are excited in both p and g modes .