Monthly Notices of the Royal Astronomical Society vol:444 pages:1189-1204
We report the results of a numerical study on the initial formation stages of low-mass protostel-
lar binary systems. We determine the separation of protostellar binaries formed as a function
of the initial thermal state by varying the initial temperature in a slightly modified version of
the initial temperature of the cloud and the initial amplitude of azimuthal density perturbation
A. For A =10 per cent, variations of only 1 K below 10 K lead to changes of up to 100 au (i.e.
of the order of 30 per cent) in the instantaneous separation, whereas for this small A the initial
temperatures above 10 K yield, instead of a binary, a single low-mass fragment that never
reaches protostellar densities. Protostellar binaries, however, do emerge when the perturbation
amplitude is increased from 10 to 25 per cent. We also investigate the impact of the critical
density which governs the transition from isothermal to adiabatic thermodynamic behaviour
of the collapsing gas. We find that the critical density not only affects the overall structural
evolution of the gas envelope, but also the size of the rotating disc structures formed during
collapse as well as the number of protostellar fragments resulting from the final fragmentation
of the discs. This mechanism can give rise to young protostellar objects constituting bound
multiple stellar systems.