A re-examination test for three-dimensional protostellar collapse codes

The standard isothermal test case of protostellar collapse and binary fragmentation, originally advanced by Boss & Bodenheimer (1979), is here re-investigated using a secondorder-accurate hydrodynamic code written in spherical coordinates. The new test calculation employs a form of the initial m = 2 non-axisymmetric perturbation that is, in contrast with that used in all previous calculations, consistent with the demands of regularity of the density at the coordinate singularities. The results of the first evolution indicate that a major protostellar binary connected by a thin bar forms, followed by fragmentation of the bar into two more condensations. As the model is evolved further, the binary condensations are seen to sub-fragment while most of the residual bar material goes into forming two additional clumps; the full process resulting in the formation of a protostellar core of eight linearly arranged condensations. Thus the assumption of a regular density perturbation results in a completely different outcome for the standard isothermal test case. The results are shown to be numerically robust and the new model provides a more consistent calculation case for testing the reliability of future three-dimensional protostellar collapse codes.