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Session 71 - Stellar Activity/Starspots.
Display session, Thursday, June 13
Tripp Commons,
We have monitored the Luminous Blue Variable (LBV) AG Car during its recent activity state by means of ultraviolet and optical spectropolarimetry. Optical spectropolarimetry was obtained at the Anglo-Australian Telescope at 5 epochs between 1991 and 1995. Ultraviolet spectropolarimetry was obtained at 4 epochs between 1991 and 1993 with the Hubble Space Telescope, and at 1 epoch in 1995 with the Wisconsin Ultraviolet Photo-Polarimeter Experiment. The data set includes two near-simultaneous ultraviolet-optical observations in 1991 and in 1995.
Based on a sub-set of 3 of the optical observations, Schulte-Ladbeck et al. (1994, ApJ, 429, 846) proposed that the polarization of AG Car is in part intrinsic and due to electron scattering. This polarization was found to be variable along a preferred axis that coincides with the long axis of the nebula, and to change sign. The amount of intrinsic polarization derived depends critically on the value of the interstellar polarization.
In this poster paper we shall discuss how the parameters derived by Schulte-Ladbeck et al. (1994) hold up when confronted with additional data. The ultraviolet polarization and new optical polarization data across the H_\alpha emission line provide better constraints on the interstellar foreground polarization. The longer time-interval covered by the observations allows us to investigate how the polarization changed as the activity state of AG Car progressed, and this provides new information on changes in the electron density distribution near AG Car with time.
This work was supported by NASA in part through grant number AR-04919.01-92A from the Space Telescope Science Institute, by NAS5-26777, and by NAG8-1073.
