Inward Motions in Starless Dense Molecular Cloud Cores by Dr. Tyler Bourke (CfA)   The search for and study of inward motions in dense cores has a checkered history. While the inside-out collapse model of Shu provides a good description of infall for cores that have already formed a protostar, no such model exists for the starless (or pre-stellar) phase, when a core may be slowly evolving and contracting. One problem is that the commonly used kinematic tracers (e.g., CS) deplete in the dense centers of starless cores, while the non-depleting N_2H^+ is not optically thick and so is not sensitive to inward motions in data with modest S/N. With the Kitt Peak 12-m and IRAM 30-m radio telescopes we have obtained very high S/N (>100) data on N_2H^+ toward 4 starless cores which have indications of infall in CS. Source models for these cores provide strong contraints on many parameters, such as the variation of density and abundance with radius, and allow us to model the very sensitive data we have obtained with different infall model and velocity profiles. I will present some early model testing and discuss the implications.