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SPRG Seminars - Archive
May 2 , 2006:
GBT Measurements of the Zeeman Effect in the Orion Molecular Complex
Tim Robishaw, UC Berkeley / Department of Astronomy
A detailed inspection of the polarization properties of the 100-m Green Bank Telescope (GBT) 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. Recent GBT detections of Zeeman splitting of the 21-cm line in emission will be presented. First, the measured polarization properties of the GBT will be reviewed. Next, detection of the 8 $\mu$G 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 an interstellar helical magnetic field. If time permits, preliminary results from other GBT observations will be presented.