Evolution of interstellar dust grains in molecular cloud envelopes: observational imprints and theoretical expectations

Star formation takes place inside cold, dense clouds of molecular material (molecularclouds) that experience a hierarchical fragmentation process. Inside these clouds the material organises itself in lamentary structures, with a density increasing at smaller scales where stars are eventually formed. The evolution ofthese clouds is aected by the injection of energy into the system. It is now widely accepted that magnetohydrodynamic turbulence contributes to sustain a molecular cloud against collapse and in consequence, directly inuences the star formation eciency. Magnetic elds, therefore, are a fundamental shaping agent of molecular clouds. The most external layers of these clouds, the so-called molecular cloud envelopes, are partially ionised due to their exposure to the ambient radiation field and hence are eectively coupled to the magnetic field. This coupling favours the propagation of hydromagnetic waves inside the clouds, increasing the turbulent state of the gas...