DYNAMICAL FRICTION FOR COMPOUND BODIES

In the framework of the fluctuation-dissipation approach to dynamical friction, we derive an expression giving the orbital energy exchange e xperienced by a compound body, as it moves, interacting with a non-hom ogeneous discrete background. The body is assumed to be composed of pa rticles endowed with a velocity spectrum and with a non-homogeneous sp atial distribution. The Chandrasekhar formula is recovered in the limi t of a point-like satellite with zero velocity dispersion and infinite temperature moving through a homogeneous infinite medium. In this sam e limit, but dropping the zero satellite velocity dispersion (sigma(s) ) condition, the orbital energy loss is found to be smaller than in th e sigma(s) = 0 case by a factor of up to an order of magnitude in some situations.