Three-dimensional Structure of the Io Plasma Torus from Ground-based Images

Details Three-dimensional Structure of the Io Plasma Torus from Ground-based Images Three-dimensional Structure of the Io Plasma Torus from Ground-based Images

Oct 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000dps....32.3510w&link_type=abstract

American Astronomical Society, DPS Meeting #32, #35.10; Bulletin of the American Astronomical Society, Vol. 32, p.1059

Astronomy and Astrophysics

Astronomy

Scientific paper

Ground-based imaging has provided key constraints on the structure of the Io plasma torus (e.g., Schneider & Trauger, ApJ. 450, p. 450, 1995), but most analyses have not tapped the full potential of the data. In most cases, images are analyzed for peak intensities, relative intensity variations, or overall morphology. One study of longitudinal variations showed the value of detailed numerical modeling (Schneider, N. M. et al. , "On the nature of the l III brightness asymmetry in the Io torus", JGR, 102, 19823-19833, 1997.), but the fitting algorithm was not sufficiently robust or efficient to extend to other data. We report on a comprehensive effort to derive the three-dimensional structure of the torus using an automated fitting algorithm. The image database includes the S+ images from Schneider & Trauger 1995, but additional images from other nights and other wavelengths will be added. The core of the fitting algorithm is the Colorado Io Torus Emissions Package (CITEP), a routine which simulates torus intensities based on plasma property inputs (Taylor, M.H et al. , "A comparison of the Voyager 1 ultraviolet spectrometer and plasma science measurements of the Io Plasma Torus", JGR . 100, 19541-50, 1995.). Our fitting algorithm uses IDL's down-hill simplex method to minimize a modified reduced-χ2 goodness of fit measure, finding densities and ion temperatures over the 4.5-6.5 Rj range. Fitting a single image provides these quantities at the torus 'ansas'; the three-dimensional structure comes from fitting a series of images spanning a complete rotation. Our results will focus on the longitudinal variations in density and ion temperature, and changes in structure from night to night. We will also extend modeling to S++ in order to place better constraints on overall plasma properties. This work has been supported by NASA's Planetary Astronomy Program.

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