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Session 78 - Stars - Young and Old, Large and Small.
Display session, Wednesday, January 15
We present imaging polarimetry of the ``Homunculus" and extended nebulosity around the luminous, hot star \eta Car. Observations were obtained with the WFC2 in filters F390N (``U"), F555W (V), and F656N (H\alpha) on two occasions, 1996 May 13 and July 7. At each epoch, we gathered images exposed to different flux levels, without polarizer filters as well as with polarizer filters thus giving three relative polarizer orientations spaced by 60^o each. We report on our attempts to calibrate the V-band imaging polarimetry to derive the linear percentage polarizations and position angles across the image.
A ground-based polarization map of the Homunculus in the V band was published by Warren-Smith et al. (1979, MNRAS, 187, 761). It was binned to a spatial resolution of 0.7"x0.7" per bin. This map serves to show the overall behavior of the linear polarization across the Homunculus, in particular it demonstrates that the polarization vectors follow the centro-symmetric pattern expected of a reflection nebula.
Even with just a calibration of the relative intensities through the different polarizer filters in place at this time, it is already apparent that the wealth of detailed spatial structure seen in direct HST images of \eta Car also occurs in the polarization. We discuss the morphologies of our V-band direct and polarization images with an emphasis on flux and associated polarization variations on small spatial scales, and their implications for the three-dimensional structure of the nebulosity around \eta Car as well as the properties of the dust.
This work is supported by STScI/AURA grant GO-05840.01-94A.
Program listing for Wednesday