Why stars inflate to and deflate from red giant dimensions – II. Replies to critics

Abstract

ABSTRACTIn a 1992 paper of ours, the role of opacity-driven thermal instabilities in shaping the course of stellar evolution was amply illustrated. This included the classical issue of ‘why stars become red giants’ as well as the subsequent formation of extended ‘Cepheids’ blue loops during the helium-burning phases. Our explanation of these evolutionary phenomena has occasionally been dismissed with just a few words in refereed or non-refereed publications. In a recent case, the fact that over the years I have not replied to these criticisms was interpreted as evidence that they were well founded. In this paper, it is made clear that this is not at all the case: the leading role of such instabilities is instead reaffirmed and the criticisms are shown to be insubstantial.