The evolving velocity field around protostars

Stars form as a result of gravitational collapse of an interstellar molecular cloud. In the process, a circumstellar disk, often referred to as a protoplanetary disk, is formed as well as a result of the net angular momentum of the parental cloud. This thesis addresses several questions about the formation of this disk and, in particular, the evolution of the velocity field surrounding the young star. The composition of the velocity field (i.e., the ratio of infall to rotation) can be use to trace the evolution of young stellar objects. This method of characterizing the evolutionary stage of protostars is applied to two objects, NGC1333-IRAS2A and L1489 IRS, the first of which we find to be a very young object while the latter is significantly more evolved. In addition, one chapter of this thesis presents a new radiation transfer code which has been developed by the author.UBL - phd migration 201