CHEMICAL EVOLUTION IN CIRCUMSTELLAR STRUCTURE OF B5 IRS1 - COMMENT

We show that the observations of Kelly, Macdonald & Millar provide a s trong indication of the freeze-out of molecules on to dust, but they d o not constrain the cyclic models of regions of low-mass star formatio n because the observed sources are the remnants of core collapse and a re not in one of the phases of evolution treated in the cyclic models. We discuss observations that are needed to provide tests of the cycli c models.