The spin - 1 electromagnetic vertex function

The e3 contribution to the electromagnetic vertex function of spin -1 particles is calculated in the framework of source theory. A magnetic moment of arbitrary strength kappa is included in the primitive interaction. In particular, the quadrupole form factor is shown to be finite with no need of adding any contact term if and only if kappa=1. A general discussion of the contact terms is included in the present work and the explicit expressions of the form factors are obtained along with their asymptotic behaviour, when kappa=1. The dynamically induced quadrupole moment, in that case, is calculated to be α/18π, and the associated spectral form is superconvergent. (author)