Numerical simulations of triggered star formation. I. Collapse of dense molecular cloud cores

Results from numerical simulations of shock waves impacting molecular cloud cores are presented. The three-dimensional smoothed particle hydrodynamics code used in the calculations includes effects from a varying adiabatic exponent, molecular, atomic, and dust cooling, as well as magnetic pseudofluid. The molecular cloud cores are assumed to be embedded in background cloud material and to have evolved into their preimpact state under ambipolar diffusion. The shock wave is assumed to be locally plane parallel and steady. The results are sensitive to the thermodynamics employed in the calculations, because it determines the shock structure and the stability of the core. Shocks with velocities in the range of 20-45 km s(-1) are capable of triggering collapse, while those with lower speeds rarely do. The results also depend on the properties of the preimpact core. Highly evolved cores with high initial densities are easier to trigger into collapse, and they tend to collapse to a single point. Less evolved cores with lower densities and larger radii may fragment during collapse and form binaries.