Circular Polarization of Circumstellar Water Masers: Magnetic Fields of AGB stars
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We present circular polarization measurements of circumstellar water masers around 2 Mira variables and 4 supergaint stars. Both an LTE and non-LTE method are used to analyze the circular polarization and total intensity spectra and to obtain the magnetic field strength. The non-LTE method is found to be able to reproduce the observations best. Using this, we find fields from a few hundred milliGauss up to a few Gauss, indicating a solar-type r^(-2) dependence of the magnetic field on the distance, which leads to stellar surface magnetic fields of up to several hundred Gauss. No linear polarization is detected to less than 1.5%.
5 pages, 2 figures; to appear in the PASP conference proceeding of the VLBA 10th Anniversary Meeting
5 pages, 2 figures; to appear in the PASP conference proceeding of the VLBA 10th Anniversary Meeting