Sensitivity of the Blue Loops of Intermediate-Mass Stars to Nuclear Reactions

Abstract

We investigate the effects of a modification of the $^{14}$N(p,{\gamma})$^{15}$O reaction rate, as suggested by recent evaluations, on the formation and extension of the blue loops encountered during the evolution of the stars in the mass range 5M$_{\odot}$ to 12M$_{\odot}$. We show that the blue loops of stars in the mass range 5M$_{\odot}$ to 8M$_{\odot}$, that is the range of super ABG stars, are severely affected by a modification of the important $^{14}$N(p,{\gamma})$^{15}$O reaction rate. We also show that the blue loops can be restored if envelope overshooting is included, which is necessary to explain the observations of the Cepheid stars.