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Paper: Circular Polarization of Circumstellar H2O Masers: Magnetic Fields of AGB Stars
Volume: 340, Future Directions in High Resolution Astronomy: The 10th Anniversary of the VLBA
Page: 394
Authors: Vlemmings, W.; Diamond, P.; van Langevelde, H.J.
Abstract: We present circular polarization measurements of circumstellar H2O 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%.
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