SIMULATION OF POLARIZATION MAPS .1. PROTOSTELLAR ENVELOPES

We developed a Monte Carlo code for the computation of polarization ma ps. This code includes multiple scattering and allows the computation for arbitrary dust configurations. In our model, we consider both the radiation of the central energy source and the thermal emission of the circumstellar dust. As one of the first applications of our code, we present polarization maps for 2D hydrodynamical models (for two time s teps of evolution: 32010 and 86222 yr) of a 1 M. rotating molecular cl ump which evolved into a protostar surrounded by a disk and envelope ( Yorke et al. 1993). For deriving the polarization patterns, we used tw o populations of the DL-MRN model - the diffuse ISM-population (radii between 0.005 and 0.25 mum) and a population with only larger grains ( radii between 0.1 and 1 mum). We calculated the polarization maps for 11 wavelength bands between 0.55 mum (V) and 1.3 mm. The computed maps agree with the typical features of the observed polarization maps of circumstellar regions around young stellar objects (YSOs). The grains in the optically thin lobes scatter the light only once. Therefore, th e radiation from these lobes is strongly polarized and has a centro-sy mmetric polarization pattern. For the inner regions of the dust disk w hich are optically thick, the polarization vectors are aligned and par allel to the disk plane. In the optically thin outer disk regions, the pattern is centro-symmetric again. The computed maps give evidence th at the particles are larger than assumed in the standard MRN model.