  We study the structure of cosmic strings produced at the breaking of an
anomalous U(1) gauge symmetry present in many superstring compactification
models. We show that their coupling with the axion necessary in order to cancel
the anomalies does not prevent them from being local, even though their energy
per unit length is found to diverge logarithmically. We discuss the formation
of such strings and the phenomenological constraints that apply to their
parameters.
