Opacity effects on the evolution of massive stars

An in-depth analysis of the stellar matter resistance to energy transport, the opacity, in the context of massive stars with high Zero Age Main Sequence (ZAMS) mass is performed. The opacity of astrophysical plasmas stands up as key in Stellar Evolution Codes (SECs) input physics, as it is know to dramatically affect model predictions of structural as well as evolutionary properties of stellar objects; by virtue of this paramount role, stellar plasma’s opaqueness is examined both as a stand-alone micro- physical process and as the possible origin of consistent evolutionary effects. The implementation, in the PAdova TRieste Evolutionary Code (PARSEC), of a refined sub-routine for relativistic electron scattering, with arbitrary degree of degeneracy, is followed by a thorough discussion of its consequent evolutionary impacts, within a varied stellar models grid. Furthermore, the author argues about the importance of thermal conductivity in the most advanced evolutionary stages, thus proceeding with its inclusion in the code at the highest temperature range. Lastly, the work tests a new prescription, for atomic and molecular transitions, still in preparation at the Padova group; model tracks of selected ZAMS from the grid are comprehensively described, offering great insights on the cooler temperatures’ opacity effects on massive stars evolution.