Understanding properties of dust in star forming clouds: polarization vs extinction

A. K. Sen*
Department of Physics, Assam University, Silchar 788 011, India

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There are evidences that the small compact clouds (also known as Bok Globules) are undergoing gravitational collapse and some of them may form low mass stars. But as these clouds undergo gravitational collapse, the ambient magnetic field plays a key role in the collapse dynamics. The strength and geometry of the magnetic field are normally estimated through the polarimetry of stars background to the cloud. The optical polarization is caused by selective absorption of background starlight by the magnetically aligned dust (grain) present in the cloud. When observed in NIR (and sub-mm), the same grains are seen in thermal re-emission. In order to study the role of grains and magnetic field, often extinction measurements are also made in such clouds. With these aims, recently such clouds have been studied in photometry, polarimetry and spectroscopy. These results are discussed with possible interpretations.

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Keywords : stars: formation – ISM: dust – extinction