Chemical limit cycles for models of a region of low-mass star formation

Barnard 5 (B5) is a nearby, clumpy region in which low-mass star formation is occurring. We have calculated the chemical evolution for three variants of the dynamics of B5. In all of these models, interclump gas collapses to produce clumps which are dispersed by the stars which form; molecular gas cycles repeatedly between clump and interclump phases and during the dispersal interval may mix with ionized gas in the stellar winds. We find that the general chemical structure attains an approximate limit in each of these models. During each dynamical cycle in each model, the molecular abundances vary substantially as functions of time; the time variations differ markedly between the models. The results of high resolution mapping of chemical abundances in B5 should reflect these substantial abundance variations and permit the determination of the dynamical cycling time scales including those associated with the survival of clumps and the interclump medium. (author)