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T. Robishaw, C. Heiles (UC Berkeley)
A detailed inspection of the polarization properties of the 100-m Green Bank Telescope (GBT) by the authors has revealed that the GBT should be unparalleled among large single-dish radio telescopes for making Zeeman-splitting measurements of spectral lines in emission. The off-axis design and unblocked aperture of the GBT provide a characterizable polarized beam structure with negligible response outside of the main beam. This talk will focus on recent GBT detections of Zeeman splitting of the 21-cm line in emission. First, detection of the 8 \muG line-of-sight magnetic field towards the North Celestial Pole will be discussed. Then results will be shown from two slices across the major axis of a filamentary molecular cloud in Orion. The measured line-of-sight fields in combination with plane-of-sky polarization measurements suggest that this may be the first evidence of a helical magnetic field. Support for this work was provided by the NSF through award GSSP 05-0004 from the NRAO.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.