SiO Maser Polarization as a Probe of AGB Circumstellar Environments
Dr. Taylor Tobin
Postdoctoral Research Associate, Department of Physics, University of Notre Dame
Observations of SiO maser polarization with Very Long Baseline Interferometry may allow us to study the structure and magnitude of the magnetic field in the near circumstellar environment of Asymptotic Giant Branch stars with sub-milliarcsecond resolution. However, other mechanisms, such as anisotropy, may also contribute to the observed maser polarization. Before the observed polarization may be used to definitively study these environments, the physical processes that contribute to it must be constrained. Thankfully, the expected behavior of the resulting polarization varies by theory. Maser features that exhibit an internal change of about 90° in the orientation of their linear polarization can be utilized as a test of several maser polarization theories. In this talk, I will discuss the multi-epoch analysis of the linear and circular polarization in a single v= 1, J = 1-0 SiO maser feature toward the Mira variable, TX Cam, that exhibits this internal polarization rotation. This analysis represents not only the first analysis of the polarization angle profile across an SiO maser feature with a ~90° linear polarization rotation, but also the most robust data sample for circular polarization analysis of SiO masers in these environments. I will compare our results to the predictions of several maser polarization theories and discuss possible explanations for discrepancies, along with ongoing theoretical development. Finally, I will discuss previous detections of polarization variation that could be due to surviving Jovian magnetospheres within the AGB circumstellar envelope and current efforts to follow up on these claims.