THE MULTI-GAUSSIAN EXPANSION METHOD - A TOOL FOR BUILDING REALISTIC PHOTOMETRIC AND KINEMATICAL MODELS OF STELLAR-SYSTEMS .1. THE FORMALISM

We introduce a new technique to build photometric and kinematical mode ls of the stellar components of galaxies. This, so-called Multi-Gaussi an Expansion method, generalizes the approach of Monnet et al. (1992). It provides accurate deconvolution of the observed surface brigthness for an arbitrary Point Spread Function, an analytical derivation of t he spatial luminosity distribution for any assumed triaxial shape and an arbitrary line of view, and a semi-analytical derivation of the rot ation and velocity dispersion laws for a large class of models with cy lindrical rotation. Other applications (e.g. the virial mass) have bee n developed.