PARAMETERS OF DISKS AROUND YOUNG STELLAR OBJECTS FROM POLARIZATION OBSERVATIONS

Linear polarization maps of young stellar objects in which a pattern of aligned polarization vectors are observed close to the central object have been interpreted recently in terms of multiple scattering in flattened, optically thick, structures (Bastien and Ménard). These patterns provide direct evidence for circumstellar disks around young stellar objects. Circular polarization, which is predicted by this model, has been detected in a few stars already; however, it cannot be accounted for by a competing suggestion in which the pattern of aligned vectors is due to dichroic extinction by aligned nonspherical grains. This fact and many other objections lead us to reject aligned grains as a suitable model for the observations. In this paper, we use the results of the Bastien and Ménard model calculations to derive some parameters which represent best the observations. In particular, the size of the optically thick part of the disks, and their inclination to our line of sight is determined for published polarization maps. The distribution of inclination angles is consistent with the expected distribution. Inclination angles and disk sizes compare well with values obtained by other methods for the objects in common.