MONTE-CARLO SIMULATION OF LIGHT-SCATTERING IN THE ENVELOPES OF YOUNG STARS

We present the results of Monte Carlo simulations of light scattering in the non-spherical envelopes of young stars. The parameters of the c ircumstellar dust envelopes have been taken from our previous single s cattering modelling of colour excesses and linear polarization variati ons during deep minima for two Herbig Ae/Be stars, UX Ori and WW Vul. The calculations of intensity and linear polarization were carried out for the wavelength range from 1000 Angstrom to 1 mu m. It is shown th at the contribution of the scattered light to the total radiation of a homogeneous oblate spheroidal envelope with a central star can reach 20-30% in the ultraviolet region of the spectrum near 2000-3000 Angstr om. A minimum influence of the dust envelope occurs at about 1 mu m wh ere the scattered stellar radiation as well as the obscurity of the st ar by circumstellar dust are already quite small, whereas thermal dust emission is not large yet. This wavelength region may be used for inv estigations of the stellar continuum unpolluted by circumstellar dust. In the envelope of WW Vul, the wavelength dependence of circumstellar extinction (taking into account scattered radiation) is almost neutra l. The degree of linear polarization does not exceed 1% for the shell models of both stars, but it increases tremendously when circumstellar dust clouds screen the star. When a full stellar eclipse occurs, the maximum polarization is 8-10% in the red part of the spectrum. The pol arization shows the local minimum at wavelengths 1300-2000 Angstrom fo r WW Vul and the double polarization reversal at wavelengths 1600-1700 Angstrom and 1900-2000 Angstrom for UX Ori.