F.Gentili, Dipart. di Fisica, Univ. di Bologna, G.Morchio, Dipart. di Fisica, Univ. di Pisa Irreversible weak limits of classical dynamical systems (64K, TeX) ABSTRACT. Limits of classical dynamical systems depending on a parameter are considered, leading in general to irreversible time evolutions and stochastic maps. The appearence of irreversibility is characterized in terms of convergence properties of the corresponding automorphisms of the observable algebra. The resulting maps are shown to be automatically \lq\lq bistochastic\rq\rq . Necessary and sufficient conditions are given for the limits to define a time independent Markov process. A model is studied for a particle interacting with fixed configurations of external obstacles.