||Circular Polarization in Scattered Light and
the Process of Light Scattering in OMC1
||449, Astronomical Polarimetry 2008: Science from Small to Large Telescopes
||Matsumura, M.; Bastien, P.
||Large linear (pl) and circular (pc) polarization observed
in star forming regions is believed to be due to scattering and/or
extinction by aligned grains, although specific details of the
process are not well known. We investigate the properties of
polarization in scattered light by aligned ellipsoidal grains with
the Fredholm integral equation method (FIM) and the T-matrix
method (Tmat), and we apply the results to the observed circular
polarization in a region south-east of the BN object (SEBN)
in OMC1. The observed large circular polarization,
pc≈0.15, can be explained by silicate grains,
if their size is 0.15–1.5 μm, and they are well aligned,
i.e. R > 0.5 where R is the Rayleigh reduction factor.
If the grains are composed of silicates and ices, our model
predicts that the degree of circular polarization pc decreases
in the 3 μm ice feature, while that of linear polarization
increases. Since this wavelength dependence is different from
that in a process of extinction, linear and circular polarimetry
of the 3 μm ice band in SEBN should be important to investigate
the details of the scattering process.