Physics
Scientific paper
Nov 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004phdt.......181f&link_type=abstract
Thesis (PhD). HARVARD UNIVERSITY, Source DAI-B 65/05, p. 2451, Nov 2004, 270 pages.
Physics
1
Scientific paper
We have observed hydroxyl masers in 15 massive star- forming regions using full-polarization VLBL Magnetic fields deduced from Zeeman pairs imply ordered fields, although unknown maser physics and evidence for Faraday rotation make full three-dimensional field reconstruction impossible. Maser clustering on 1015 cm scales suggest that some hydroxyl masers form in the region between the ionization and shock fronts around massive stars, while collinear maser structures and velocity gradients argue for the importance of shocks on scales larger than 1015 cm as well. We have found a total of more than 100 Zeeman pairs in more than 50 massive star-forming regions from the VLA survey of OH masers. The magnetic field deduced from the Zeeman splitting has allowed us to assign an overall line-of-sight magnetic field direction to many of the massive star-forming regions. We do not find strong Galactic-scale correlations of the magnetic field direction, but our data suggest that in the Solar neighborhood the magnetic field outside the Solar circle is oriented clockwise as viewed from the North Galactic Pole, while inside the Solar circle it is oriented counterclockwise. This reversal is in agreement with results obtained from pulsar rotation measures. We have observed H I absorption against 20 ultracompact H II regions, thereby resolving the kinematic distance ambiguity to these sources. The HWHM of the distribution of source height above and below the Galactic plane is found to be 35 ± 2 pc within the solar circle. The vertical height distribution is used to investigate the predictive accuracy of the Galactic latitude in resolving the kinematic distance ambiguity to UCH II regions without the need for H I observations. For a large difference between far and near kinematic distances, high accuracy can be achieved by choosing the kinematic distance closer to 1.84 | b|-1 kpc, where b is the Galactic latitude in degrees.
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