A. Burkert et P. Bodenheimer, MULTIPLE FRAGMENTATION IN COLLAPSING PROTOSTARS, Monthly Notices of the Royal Astronomical Society, 264(4), 1993, pp. 798-806
Hydrodynamical calculations in three space dimensions of the collapse
of an isothermal, rotating 1-M. protostellar cloud are presented. A nu
merical algorithm involving nested subgrids is used to resolve the reg
ion of initial binary formation in the central part of the protostar.
An extensive series of numerical tests confirms the accuracy of the co
mputer program. Comparisons are given with a standard test case of bin
ary fragmentation in a collapsing isothermal cloud of initially unifor
m density. In a simulation with a 50 per cent initial perturbation a b
inary is clearly formed. In another simulation with a 10 per cent init
ial perturbation, however, calculations show the initial formation of
a binary and a connecting bar, followed by fragmentation of the bar. T
he binary components are surrounded by accretion discs of radius appro
ximately 100 au. This result is shown to be independent of the grid sp
acing employed. It is suggested that the further evolution of this sys
tem is likely to produce some isolated low-mass fragments. In both the
above cases (i.e. 50 and 10 per cent perturbations) a detailed analys
is of the momentum of the forming fragments indicates that they are in
itially on a highly eccentric orbit. The subsequent interaction of eac
h fragment with the other's accretion disc could result in circulariza
tion and the formation of a shorter period multiple system.