AAS 201st Meeting, January, 2003
Session 49. Eta Carinae, LBVs, and Circumstellar Disks
Poster, Tuesday, January 7, 2003, 9:20am-6:30pm, Exhibit Hall AB

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[49.12U] Circumstellar Disk Diagnostics from Polarimetry and Infrared Excesses

A.C. Gault, K.S. Bjorkman, J.E. Bjorkman (U. Toledo)

The circumstellar disks of B-type emission line stars polarize the light emitted by the star and also cause excess infrared radiation. The observed polarization and infrared excess are affected by both the disk inclination and optical depth. We have modeled the effects of these two parameters on the predicted polarization and infrared excesses of Be stars over a range of stellar temperatures, with the disk temperature set to a value 75% of the stellar temperature. Our models produce a grid with lines of equal inclination and equal density. In principle, such a grid should enable us to determine the inclination angle and optical depth of a circumstellar disk by measuring the polarization level and infrared excess from the system. Our results reproduce the distinct triangular shape characteristically seen in empirical plots of observational data (polarization vs. infrared excess). In addition, an explanation for the observed upper limit of the polarization is suggested. Once the disk inclination reaches 70 to 75 degrees, the polarization reaches a maximum. It then decreases again at higher inclinations until, nearing 90 degrees, the polarization is about half the maximum value. Thus, we find that the upper limit produced by a specific model is defined by a combination of the maximum polarization and the maximum infrared excess predicted. We currently are extending this work to incorporate a more realistic Keplerian model for the disks.

This work has been supported by a NSF REU grant to the University of Toledo, and by NASA grant NAG5-8054. AG acknowledges support from an Ohio Space Grant Consortium Scholarship.

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