A Faraday Rotation Measure Anomaly Due to the Cygnus OB1 Association

Type Conference Paper
Names Catherine Whiting, S. R. Spangler, L. D. Ingleby, L. M. Haffner
Proceedings Title Bulletin of the American Astronomical Society
Conference Name American Astronomical Society, AAS Meeting #211, #139.12
Volume 39
Pages 987
Date December 1, 2007
URL http://adsabs.harvard.edu/abs/2007AAS...21113912W
Library Catalog NASA ADS
Abstract A study of rotation measures through the Cygnus region of the galactic plane by Lazio et al (ApJ 363, 515, 1990) revealed a large range in rotation measures, -100 to 700 rad/m2 , over a region of about 2-3°, possibly indicating a reversal of the direction of the galactic magnetic field. We present new polarization observations of the same sources observed by Lazio et al. The observations were made with the Very Large Array at 4585 and 4885 MHz. We confirm the rotation measure anomaly and offer a possible explanation. We show that a simple model of an expanding plasma shell can account for a large range in rotation measures, quantitatively similar to that observed, over a small angular scale. Details of the physical model of the shell will be presented as well as evidence for the existence of such a shell from the Wisconsin H-Alpha Mapper survey of ionized hydrogen along the line of sight of our sources.
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