Notes. The distributions of the values considered in the parameter space are: temp – by equal steps in temperature of the grain size with the steepest radial temperature gradient, lin – linear, log – linear in the logarithm of the parameter, fixed – fixed value (no distribution at all), cos – linear in the cosine of the parameter, cont – continuous (scaling of the disk mass to minimize the χ² for given values of all other parameters). Values marked with an asterisk are (very close to) the boundaries of the parameter space explored and cannot be considered as reliable (in case of best-fit parameters real values may lie outside the parameter space explored, in case of confidence levels uncertainties are probably larger here). The values for τ_⊥ (vertical geometrical optical depth), and t_coll (collisional lifetime of the dust following Backman & Paresce 1993), and t_PR (Poynting-Robertson life time of dust grains, see Sect. 3.1 for details) are computed for the best-fit models at representative positions in the disk.