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Constraining Theories of SiO Maser Polarization: Analysis of a π/2 EVPA Change

Published online by Cambridge University Press:  16 July 2018

T. L. Tobin ,
A. J. Kemball  and
M. D. Gray
T. L. Tobin
Affiliation:
Department of Astronomy, University of Illinois at Urbana-Champaign1002 W. Green Street, Champaign, IL 61801, USA Jodrell Bank Centre for Astrophysics, Alan Turing Building, University of ManchesterManchester M13 9PL, UK
A. J. Kemball
Affiliation:
Department of Astronomy, University of Illinois at Urbana-Champaign1002 W. Green Street, Champaign, IL 61801, USA
M. D. Gray
Affiliation:
Jodrell Bank Centre for Astrophysics, Alan Turing Building, University of ManchesterManchester M13 9PL, UK
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Abstract

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The full theory of polarized SiO maser emission from the near-circumstellar environment of Asymptotic Giant Branch stars has been the subject of debate, with theories ranging from classical Zeeman origins to predominantly non-Zeeman anisotropic excitation or propagation effects. Features with an internal electric vector position angle (EVPA) rotation of ∼π/2 offer unique constraints on theoretical models. In this work, results are presented for one such feature that persisted across five epochs of SiO ν = 1, J = 1 − 0 VLBA observations of TX Cam. We examine the fit to the predicted dependence of linear polarization and EVPA on angle (θ) between the line of sight and the magnetic field against theoretical models. We also present results on the dependence of mc on θ and their theoretical implications. Finally, we discuss potential causes of the observed differences, and continuing work.

Keywords

maserspolarizationmagnetic fieldsstars: AGB and post-AGB
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 13 , Symposium S336: Astrophysical Masers: Unlocking the Mysteries of the Universe , September 2017 , pp. 53 - 56
Copyright
Copyright © International Astronomical Union 2018 

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