Models of OH Maser Variations in U Herculis

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Abstract
Arecibo spectra of the main-line OH maser emission from U Her over more than a decade show variations of the OH emission over these timescales. These observations are combined with high spatial resolution VLBA maps to investigate the changes in the velocities of the maser components. Global properties of the dust shell, such as accelerations, variations in the pump, and shellwide magnetic field changes are examined as possibilities and eliminated. A solution to the problem involving plasma turbulence and the local magnetic field is introduced, and the relevant timescales of the turbulence are calculated. The turbulent velocity field causes variations on timescales that are too long (of order centuries), while the turbulent magnetic field causes variations on appropriate timescales of a few years. A line-of-sight model of the turbulence is developed and investigated. The complete exploration of this solution requires extensive theoretical and observational work. Possible avenues of investigation of the plasma turbulence model are presented.
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