  Young open clusters are likely sites of cosmic ray acceleration as indicated
by recent detections of the TeV gamma-ray sources in the directions of two open
clusters (Cyg OB2 and Westerlund 2) and their directional proximity to some
unidentified EGRET sources. In fact, up to now a few different scenarios for
acceleration of particles inside open clusters have been considered, i.e.
shocks in massive star winds, pulsars and their nebulae, supernova shocks,
massive compact binaries. Here we consider in detail the radiation processes
due to both electrons and hadrons accelerated inside the open cluster. As a
specific scenario, we apply the acceleration process at the shocks arising in
the winds of WR type stars. Particles diffuse through the medium of the open
cluster during the activity time of the acceleration scenario defined by the
age of the WR star. They interact with the matter and radiation, at first
inside the open cluster and, later in the dense surrounding clouds. We
calculate the broad band spectrum in different processes for three example open
clusters (Berk 87, Cyg OB2, Westerlund 2) for which the best observational
constraints on the spectra are at present available. It is assumed that the
high energy phenomena, observed from the X-ray up to the GeV-TeV gamma-ray
energies, are related to each other. We conclude that the most likely
description of the radiation processes in these objects is achieved in the
hybrid (leptonic-hadronic) model in which leptons are responsible for the
observed X-ray and GeV gamma-ray emission and hadrons are responsible for the
TeV gamma-ray emission, which is produced directly inside and in dense clouds
surrounding the open cluster.
