Spectrophotometry of Cas A: Implications for Nucleosynthesis in Massive Stars

Abstract

Cas A is the prototype of supernova remnants (SNRs) in which fast-moving, chemically peculiar debris is found. The fast-moving knots have velocities 4000–8000 km/s and are composed entirely of products from advanced stages of nucleosynthesis, with essentially no hydrogen (PEIMBERT and VAN DEN BERGH [1], CHEVALIER and KIRSHNER [2]). Based on this evidence, the fast knots are generally believed to represent uncontaminated ejecta from the core of a massive star. Recent studies by FESEN et al. [3] find that the fastest knots in Cas A are very nitrogen-rich, which suggests the more specific identification of the progenitor as a WN star, and that the super-fast nitrogen knots are material from its surface. Along with the handful of remnants with similiar but less extreme properties, Cas A provides one of the few arenas where theoretical models for the evolution and explosion of massive stars can confront observational evidence VAN DEN BERGH [4]. Cas A has become all the more interesting in the wake of SN1987A, for the two objects appear to have many similarities.