The uncertain evolution of blue looping He burning stars

We investigate the evolutionary characteristics of stars in the central He burning phase, with particular attention to the problem of the loop formation and its temperature extension. One finds that in the case of a 5 M. (Y=0.25, Z=0.008) the. C-12 + alpha reaction and the release of gravitational energy govern the extension of the loop. However, as already discussed in the literature, the loops formation and extension appear not driven by a single parameter but by an interaction of several factors and strongly dependent on variations of the physical inputs within their uncertainties.