Published online by Cambridge University Press: 14 August 2015
Grain accretion processes in a protoplanetary nebula have been studied regarding: (a) the distribution function of grain velocities; (b) electrostatic and electromagnetic mechanisms between grains. The velocity distribution function has been investigated for grains embedded in a turbulent gaseous medium. Results have been obtained for protoplanetary nebula densities ranging from 10−19 to 10−10 g cm−3. Considering interactions between two grains, photoelectrically charged by galactic ultraviolet flux and by charged-particle capture, and solid-solid interactions (dipole fluctuation effect), the authors estimate the physical cross section σ(v) with respect to the geometric one σ0. Then a statistical approach for an assembly of grains gives the accretion or destruction rates for these small particles. Therefore, according to their characteristic velocities, the following processes have been studied: rupture, fusion, vaporization.