Supergiant mass loss and the Cassiopeia A progenitor

Observations of the chemical abundances in youg supernova remanants may be used, in some circumstances, to place constraints on the evolution of the progenitor stars. For example, if a progenitor was massive (M > 10 solar masses), the presence of high 14N/1H ratios in the supernova remnant can imply that substantial mass loss took place during the star's early evolution, that is, while it was an early-type supergiant. An example is the supernova remnent Cassiopeia A, which has a non-solar composition and a 14N/1H ratio which is very large in some regions. A comparison of the observed abundances in Cas A with the abundances predicted from theoretical calculations of the evolution of massive stars indicates, firstly, that the progenitor star was massive and, secondly, that substantial mass loss took place while it was an early-type supergiant. The rate of mass loss required in this case is consistent with the rates observed in early-type supergiants. (Auth.)