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The effect of a spiral-like perturbation in the orbits of an axisymmetric galactic potential is studied using surfaces of section. It is found that the perturbation induces stochasticity and diffusion of orbits in phase space.

A description of the stray-light problem based on a radiative transfer approach is presented. The 2D convolution that describes the effect of the stray-light is recovered in this formalism. The controversy raised by the old normalization condition is satisfactorily eliminated within the present description. The present formalism is applied to

Aims: To improve our understanding of substellar formation, we have performed a compositional and structural study of a brown dwarf disk. Methods: We present the results of photometric, spectroscopic, and imaging observations of 2MASS J04442713+2512164, a young brown dwarf (M 7.25) member of the Taurus association. Our dataset, combined with

In this paper we analyze the structural parameters of the dwarf galaxies in the Coma Cluster with -18

The focus of the present paper is on the detailed description of the internal structures of low mass, population II stars, to clarify some issues about these stellar models and, mainly, their present reliability for observational comparisons. We then explore 1) the role of the local convective model; 2) the differences between "grey" and "non grey"