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Session 57 - Astrophysical Diagnostics from Polarimetry.
Display session, Wednesday, June 12
Tripp Commons,
We describe a 1.2--millimeter polarimeter to be used on the Steward Observatory and Max--Planck--Institut für Radioastronomie 10--meter Submillimeter Telescope Observatory. The construction, performance parameters, and scientific purpose of the instrument are presented. The detector is a Ge bolometer with a Si absorber operated in a cavity cooled to 0.36 K by a liquid He^3 refrigerator. The bandpass has a central wavelength of 1.2 mm and a width of 0.3 mm. The system noise equivalent power is 1.5\times10^-14 W Hz^-1øver2 at 20 Hz. Polarimetric modulation is accomplished with a room temperature, rotating Rexolite half-wave plate. Unidirectional grooves provide the \lambda/2 phase shift between the orthogonal senses of polarization. The polarization analyzer is a stationary, room temperature, unidirectional wire grid that transmits only one sense of polarization with 99% efficiency. The system polarimetric efficiency is 87% and the laboratory instrumental polarization is a well defined 3.7%. Detection of a 1% linear polarization is possible at the several sigma level.
The primary scientific goal of this instrument is to probe the magnetic field orientations in the protostellar dust cores of molecular clouds. Non--spherical dust grains are aligned in the presence of a magnetic field resulting in linear polarization of the far--infrared thermal dust emission perpendicular to the magnetic field vector. Observed field orientations will be compared to protostellar molecular outflow orientations and magnetic fields on larger scales. With these comparisons we will assess the role of magnetic fields in cloud collapse and star formation.
