Published online by Cambridge University Press: 19 July 2016
The generation and maintenance of galactic magnetic fields are considered when the dynamo-acted disk is perturbed by spiral density waves. The periodic change of gaseous density and shear is coupled with the field oscillation as a dynamo wave. We find the conditions for parametric resonance which increases the efficiency of dynamos. Special attention is paid to two-armed spiral galaxies, in which the BSS field structure is possibly the most effectively excited configuration owing to the present mechanism.