AAS Meeting #193 - Austin, Texas, January 1999
Session 69. Circumstellar Material
Display, Friday, January 8, 1999, 9:20am-6:30pm, Exhibit Hall 1

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[69.01] The Polarization and Variability of Main Line OH Maser Emission from Long Period Variable Stars

J. D. Fix (U. Iowa)

The spectral shape and polarization of maser emission from the envelopes of cool stars are useful for investigating envelope dynamical and magnetic field structure. I have used 1665 MHz and 1667 MHz spectra obtained at the Arecibo Observatory at eight epochs between 1977 and 1992 to study the circular polarization and temporal variability of OH emission from the circumstellar shells of a sample of twelve long period variable stars. For about half of the stars, the polarization at 1667 MHz consistently was either weak or too small to measure. For the rest, the degree of polarization was large and variable. For each of the eight stars for which the emission at 1665 MHz was strong enough for polarization to be reliably determined, the polarization at 1665 MHz was stronger than that at 1667 MHz. All of the spectra showed temporal variability, but the time scale for significant change in the shape of the spectral line profile varied from star to star, ranging from six months to ten years. There is a strong correlation between polarization and variability in the sense that the greater the average degree of circular polarization, the shorter the time scale for variability. I interpret this result in terms of a plasma turbulent model of the region of maser production.

The author(s) of this abstract have provided an email address for comments about the abstract: john-fix@uiowa.edu

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