  Interaction between collective monopole oscillations of a trapped
Bose-Einstein condensate and thermal excitations is investigated by means of
perturbation theory. We assume spherical symmetry to calculate the matrix
elements by solving the linearized Gross-Pitaevskii equations. We use them to
study the resonances of the condensate induced by temperature when an external
perturbation of the trapping frequency is applied and to calculate the Landau
damping of the oscillations.
