Polarimetric studies on Interstellar grains

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Spectroscopy and spectro-polarimetry have been made for reddened giants and supergiants in the Galactic plane, young stellar objects dark clouds, and back ground stars of dark clouds. Reddened stars in the Galactic plane is from an I-band objective prism survey, and most of them have turned out to be moderately reddened M-type stars that are intrinsically red. Their extinction and polarization agree fairly well with the relationship in the literature ; this suggests that even in dark clouds grains produce extinction and polarization in the same manner as in diffuse clouds. From their observations, we demonstrate that some of them show deep absorption at 3.4 microns, and that the 3.4 micron absorption feature increases with the interstellar extinction.One objects show a polarization excess in the ice band at 3.0 microns. This objects would be a useful tool when studying the ice properties because it is located behind a dark cloud and free from scattering effect. Spectro-polarimetry of many young stellar objects in dark clouds are also made in the ice band. The grain alignment efficiency have been compared with a model calculation, and usual magnetic field seems to be sufficient for the alignment. On the other hand, the spectral shape of the absorption and polarization is difficult to be reproduced by laboratory analogs of the interstellar ice.A number of objects with the ice band absorption and the 3.3 micron emission feature have been found in star forming regions. Some of them require further observations of higher spatial resolution.