The interstellar medium (ISM) appears to be arranged in clouds, whose dimensions, masses and densities span a large range of scales. The structure of these objects show a high degree of complexity appearing, in the range of the observed scales, as a non-homogeneous distribution of matter. The arrangement of the ISM is clearly relevant for the study of the fragmentation of the clouds and then of the star formation processes. To quantify observationally the ISM structure, many approaches have been developed, including techniques based on fractal geometry. In this talk I will introduce, first of all, a few basic concepts of the fractal theory, and indicate their application in describing complex natural objects, and in particular astrophysical phenomena. Then, i will illustrate the properties of the so-called "fractional Brownian motion" images, which can be used also to characterize the IR/mm maps of the ISM and to carry out a quantitative description of their "structure". Among several statistical tools adopted to perform this kind of analysis, I will briefly illustrate and discuss the method of the "Delta-variance" for the determination of the fractal dimension of an observed cloud.
2009 February 18, 13:30
Centro de AstrofÝsica da Universidade do Porto (Auditorium)
Rua das Estrelas, 4150-762 Porto