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When low-mass stars form, the collapsing cloud of gas and dust goes throughseveral stages which are usually characterized by the shape of their spectralenergy distributions. Such classification is based on the cloud morphology onlyand does not address the dynamical state of the object. In this paper weinvestigate the initial cloud collapse and subsequent disk formation throughthe dynamical behavior as reflected in the sub-millimeter spectral emissionline profiles. If a young stellar object is to be characterized by itsdynamical structure it is important to know how accurately information aboutthe velocity field can be extracted and which observables provide the bestdescription of the kinematics. Of particular interest is the transition frominfalling envelope to rotating disk, because this provides the initialconditions for the protoplanetary disk, such as mass and size. We use ahydrodynamical model, describing the collapse of a core and formation of adisk, to produce synthetic observables which we compare to calculated lineprofiles of a simple parameterized model. Because we know the velocity fieldfrom the hydrodynamical simulation we can determine in a quantitative way howwell our best-fit parameterized velocity field reproduces the original. We usea molecular line excitation and radiation transfer code to produce spectra ofboth our hydro dynamical simulation as well as our parameterized model. We findthat information about the velocity field can reasonably well be derived byfitting a simple model to either single-dish lines or interferometric data, butpreferentially by using a combination of the two. Our result shows that it ispossible to establish relative ages of a sample of young stellar objects usingthis method, independently of the details of the hydrodynamical model.

Characterizing the velocity field in hydrodynamical simulations of low-mass star formation using spectral line profiles