Interstellar grain size - A look at the deviant four

Abstract

A linear polarimeter has been used to examine three of four stars (BR 545, 885, and 929 in Orion) that do not appear to fit either a simple relationship between IR excess and wavelength of maximum polarization or the simple grain-growth models of McMillan (1978). The data obtained are shown to resolve the discrepancies in the cases of BR 545 and BR 929. The polarization of BR 885 is found to be quite complex, and the data indicate that interstellar reddening, possibly caused by two large intracluster dust clouds in the line of sight, is the source of the IR excess and polarization. It is concluded that the available interstellar data for these three stars are consistent with models of accretion of nonabsorbing mantles on dust-grain cores.