Multi-line analysis of the spectra of Herbig Ae/Be stars

We present the results of the study of four Herbig Ae/Be stars (AB Aur, BD46 degrees 3471, HD250550, BD+61 degrees 154). For each of them, semi-empir ical models of the structure of their winds have been constructed; we then calculated the Na line, the Palmer discontinuity, as well as the C IV 1548 Angstrom and Mg II h or k resonance lines. Thanks to comparison with observ ational data, we have deduced constraints on the parameters of the models, which provide us with a rather good representation of the averaged structur e of the winds. Despite of the time variability of these stars, we show tha t we can gather trustworthy information on the values of the mass loss rate s of these stars. It is also shown that models with departure from spherica l symmetry are needed to account for the observed shapes of the lines. In a ddition, radiative losses due to several transitions (lines and continua) o f hydrogen have been evaluated, in order to gain more insight in the energy sources that generate the observed activity of these stars.