Magnetic diffusion and ionization fractions in dense molecular clouds - The role of charged grains
B. G. Elmegreen;
ApJ, 1979, 232, 729
ABSTRACT:The physics of magnetic diffusion in dense molecular clouds is examined, with particular attention given to the role of charged grains in
controlling the process.
The ionization fraction of dense molecular clouds in the
presence of grains is determined from considerations of charge exchange,
dissociative recombination, radiative recombination and collisions between
grains and charged species, and it is found that the inclusion of grains tends
to lower the ionization fraction for a given cosmic-ray ionization rate
and metal depletion.
The kinematics of grain motion is discussed and it is
shown that at temperatures less than 30 K, each grain alternates rapidly in
charge between -1 and 0 and thus executes periodic motion in a
self-gravitating cloud containing a magnetic field.
The full kinematics of magnetic
diffusion including the motions of ions and electrons are then examined, taking
into account the additional viscous force from charged grains, and
numerical calculations of the diffusion time scales of uniform, magnetically
supported clouds or cloud cores are presented.
KEYWORDS: charged particles, interstellar matter, ionization coefficients, magnetic diffusion, molecular collisions, plasma clouds, charge exchange, dissociation, interstellar magnetic fields, magnetic effects, particle collisions, recombination reactions, viscosity
PERSOKEY:dust, magnetic field, ,
CODE: elmegreen79