Models of OH maser variations in U Herculis

Arecibo spectra of the main-line OH maser emission from U Her over more tha n a decade show variations of the OH emission over these timescales. These observations are combined with high spatial resolution VLBA maps to investi gate the changes in the velocities of the maser components. Global properti es of the dust shell, such as accelerations, variations in the pump, and sh ellwide magnetic held changes are examined as possibilities and eliminated. A solution to the problem involving plasma turbulence and the local magnet ic held is introduced, and the relevant timescales of the turbulence are ca lculated. The turbulent velocity field causes variations on timescales that are too long (of order centuries), while the turbulent magnetic held cause s variations on appropriate timescales of a few years. A line-of-sight mode l of the turbulence is developed and investigated. The complete exploration of this solution requires extensive theoretical and observational work. Po ssible avenues of investigation of the plasma turbulence model are presente d.