Physics
Scientific paper
Jun 1991
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991phdt........21z&link_type=abstract
Thesis (PH.D.)--THE UNIVERSITY OF IOWA, 1991.Source: Dissertation Abstracts International, Volume: 52-12, Section: B, page: 645
Physics
1
Giant Stars, Sixteen 1612 Mhz Emission
Scientific paper
I have used the Arecibo radio telescope to observe seven giant OH/IR stars at 1612 MHz. The line profiles of these objects are consistent with a model in which emission arises from several thousand discrete emitting elements within circumstellar shells. I have made model line profiles which contain many, but not all, of the characteristics of the observed line profiles. Observations at 1612 MHz of six giant OH/IR stars in right and left circular polarization, utilizing high spectral resolution and sensitivity, revealed that the degree of circular polarization rarely exceeds 10% in any spectral feature. Magnetic field intensities in the regions of OH maser emission range from ~1 to ~10^2 muG. These results contrast with earlier 1612 MHz observations of several supergiant OH/IR stars, in which net circular polarizations were as high as about 40%, and in which field intensities were ~1 mG. The lower degree of circular polarization in the emission from the giants may be due both to smaller magnetic field intensities and to more efficient spectral blending. Interferometric observations of the circumstellar shell of the supergiant OH/IR star VX Sgr detected organization in the distribution of Stokes V flux over large spatial scales. Large scale organization in the spatial distribution of B flux may also exist in maps of the giant star OH 39.7 + 1.5. Evidence was also found that blending of oppositely polarized emission from spatially separated emitting elements can reduce the degree of polarization detected in single dish observations.
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