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We report on an ongoing project to measure with high resolution the magnetic field geometries in deeply embedded star forming regions. It is widely believed that magnetic fields play a crucial role in star formation on scales ranging from the stellar size to that of the parent molecular cloud. So far, measurements of the magnetic field structure have only been made on the largest scales and little is known about the structure within collapsing protostellar condensations and circumstellar disks. Interferometric imaging of linearly polarized emission from magnetically aligned dust grains can provide information on the magnetic geometry in nearby star forming regions on scales ranging from 100 to 3000 A.U.
In 1994 February we installed tunable reflecting polarizers on 5 elements of the OVRO mm interferometer. Configured as $\lambda/4$ plates the polarizers allow us to multiplex between right and left hand circular polarizations on each telescope and thus to make images using all 4 stokes parameters. Cross circular polarizations minimize the systematic errors in measuring weakly linearly polarized emission such as that expected from aligned dust grains in star forming regions.
We will present a summary of the instrument performance and results from the ongoing polarimetric observations of dust and maser emission from nearby star forming regions.
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