J.-P. Arcoragi

Fragmentation of elongated cylindrical clouds. III, Formation of binary and multiple systems

Using three-dimensional hydrodynamical simulations, the fragmentation of uniform, isothermal, elongated molecular clouds, slowly rotating around an axis perpendicular to their elongation is studied. It is argued that this process could result in the formation of binary and multiple stars. This new method for forming binary stars can explain wide binaries with large eccentricities and various mass ratios. At relatively low initial Jeans numbers (the ratio of the absolute value of gravitational to thermal energies), a simple binary system is formed. For higher initial Jeans numbers, multiple fragmentation occurs between the binary fragments, forming a multiple system

Fragmentation of elongated cylindrical clouds. I. Isothermal clouds

We present a numerical study of fragmentation in its simplest possible form : that of elongated, isothermal, axially symmetric clouds. Results have been obtained for different ratios of length to diameter, L/D, and initial Jeans numbers, J 0 (ratio of gravitational to thermal energies). We introduce initial density perturbations on the axis of otherwise uniformly dense cylinders and determine the maximum number of fragments N fmax that can form and grow for combinations of L/D and J 0 .

Fragmentation of elongated cylindrical clouds. IV - Clouds with solid-body rotation about an arbitrary axis

Results of 3D hydrodynamic collapse calculations of elongated isothermal clouds with solid-body rotation about an arbitrary axis are presented. Four different modes of fragmentation are identified. In all evolutions that formed more than one fragment, a structural fragmentation mode occurred first, forming condensations on each side of the cylinder. It is shown that gravitational torques and tidal effects control most of the fragmentation and coalescence which occur. The fragmentation processes and gravitational torques can also reduce the fragments specific angular momentum by up to two orders of magnitude compared to that of the parent cloud. This is consistent with the inferred value of the specific angular momentum of the initial protosolar nebula.

Fragmentation of elongated cylindrical clouds. II : Polytropic clouds

A numerical study of the fragmentation of elongated, polytropic, axially symmetric clouds is presented. Results have been obtained for various ratios of length to diameter L/D, polytropic constant γ, and initial Jeans number J 0 (ratio of the absolute value of gravitational to thermal energies). Initial density perturbations on the axis of otherwise uniformly dense cylinders are intriduced and the maximum number of fragments that can form and grow for combinations of L/D, γ, and J 0 are determined.