Instrument

The Io plasma torus is an observational challenge: its kilorayleigh or less optical emissions are swamped by the 6 megarayleigh reflected continuum from nearby Jupiter; the torus "wobbles" about Jupiter, which in turn canot be tracked sidereally; the high time-variability of the torus requires a long timebase of observations to study properly; and the precise spatial relationship of the emissions to Jupiter is critical to interpretation of any imaging data. We use the McMath-Pierce west auxiliary telescope because it has no "spider" which would scatter light from Jupiter into the field of view, and because it is possible to obtain large blocks of observing time. Our instrument, a broadband imager using a CCD and interference filter (fig. 1), uses a special assembly at the entrance aperture: the two sides of the torus are imaged in the clear areas on the sides of the tilted rectangular aperture, while a neutral density filter in the aperture center reflects a bright image of Jupiter to the guide camera and simultaneously transmits an attenuated image to the CCD. Adjustable bars mounted beside the aperture are used to block jovian moons when they enter the field of view. The entire assembly is built on a rotator which maintains the orientation of the torus on the entrance mask throughout the night.

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Copyright © 1999 R. Carey Woodward, Jr. and/or the Board of Regents of the University of Wisconsin, as their interests may lie. All rights reserved. When citing this paper, please use this information.