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Session 47 - Circumstellar Disks & Shells.
Display session, Thursday, January 08
Exhibit Hall,
We present preliminary results of VLBI observations of the 1665/1667 MHz OH maser emission in the circumstellar dust shell of the long-period variable, U Her. We have obtained maps of both the right and left circularly polarized emission in both the 1665 MHz and 1667 MHZ lines. The maps have a spatial resolution of about 10 milliarcseconds and a spectral resolution of about 0.1 km/s. These maps show that the OH emission from U Her arises from several dozen spatially distinct components. The components can be identified with spectral features observed in high resolution OH spectra obtained over more than a decade at the Arecibo Observatory. We will use the VLBA maps to investigate whether secular changes in the appearance of OH spectra of U Her are due to changes in the Zeeman splitting, acceleration, and pumping of maser components or a combination of these factors.
