IN SEARCH OF EVIDENCE FOR PROTOSTELLAR COLLAPSE - A SYSTEMATIC STUDY OF LINE FORMATION IN LOW-MASS DENSE CORES

We present radiative transfer models of low-mass dense cores as depicted in two theoretical models of protostellar collapse: the Larson-Penston flow and the theory of Shu and coworkers based on the "inside-out collapse " model. In particular, line profiles of the first three rotational transitions of the CS molecule are calculated for hypothetical dense cores evolving according to these theories. The results are compared with CS observations of nearby dense cores. It is shown that the Larson-Penston flow overestimates the velocity width of the CS lines by a large margin and cannot be reconciled with the observations. In contrast, the theory of Shu and coworkers predicts the right velocity width for the CS lines during the formation stage of dense cores. The models indicate that " inside-out " collapse should significantly enhance the CS line widths and the enhancement should be easily observable, particularly at high resolution. A list of line properties are presented for hypothetical dense cores undergoing " inside-out " collapse. These properties are found to be unique to collapse motions; hence, they can be used as a guide in searching for protostellar collapse.