Ultraviolet/Visible Spectropolarimetry of $\alpha$~Orionis
Session 5 -- Chromospheres/Coronae/Active Binaries
Display presentation, Monday, 30, 1994, 9:20-6:30

## [5.07] Ultraviolet/Visible Spectropolarimetry of $\alpha$~Orionis

K.H. Nordsieck, L. Rao, M.R. Meade, C.M. Anderson, B.L. Babler, K.S. Bjorkman, A.D. Code, M. Taylor, N.E. Zellner (U. Wisconsin), A.M.Magalh\~aes (U. Sao Paulo), G.C.Clayton (U. Colorado), R.E.Schulte-Ladbeck (U. Pittsburgh), B.A.Whitney (CFA)

In December 1990, spectropolarimetric observations were obtained of the M supergiant $\alpha$~Orionis, from 1500-3300 $\AA$ with the Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE) aboard the Astro-1 mission, and from 3200-7600 $\AA$ at the University of Wisconsin Pine Bluff Observatory. Analysis of these data indicates that 1) there are at least two independent polarization mechanisms, with different geometries, which contribute to the intrinsic linear polarization in both the visible and ultraviolet; 2) the polarization rises dramatically to 2\% at 3000 $\AA$, then drops steeply below 2900 $\AA$; and 3) the MgII $\lambda$2800 emission line is depolarized. This indicates that photospheric and chromospheric processes are involved in the production of the intrinsic polarization, through pronounced surface intensity variations scattered within the atmosphere and/or in a dusty envelope. Several models of intrinsic polarization from hot spots, atmospheric scattering, and dust scattering will be compared with the observations. An ongoing monitoring program and a spectropolarimetric survey of Luminous Red Variables will also be described.

This work has been supported by NASA contract NAS5-26777 to the University of Wisconsin.