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J. M. Carvano (The University of Arizona/Observatório Nacional), D. W. Mccarthy (The University of Arizona), R. Binzel (Massachusetts Institute of Technology), J. Drummond (Phillips Lab), M. Gaffey (Rensselaer Polytechnic Institute), K. Hege, L. Lebofsky (The University of Arizona), P. Thomas (Cornell University), E. Wells (Computer Sciences Corporation), B. Zellner (Georgia Southern University), A. Storr (Towson University), J. Hinz (The University of Arizona)
Being the biggest asteroid with a reasonably intact basaltic crust, 4 Vesta is a pivotal object to the understanding of the early history of the Solar System. Attempts to map the mineralogical variations on its surface include earth-based spectroscopy on the 0.8-2.5\mu m range as well as disk-resolved observations with the HST between 0.4-1.0\mu m and JHK imaging with adaptive optics with the Keck Telescope. However,the observations of 4 Vesta during the 1997 opposition with the HST/NICMOS are the first to combine spatial resolution and full rotational coverage with a set of filters that covers the most mineralogically relevant spectral features of HED assemblages.
The NICMOS data were all acquired within a 5-day interval, with Vesta's sub-earth latitude varying from -2.8 to -3.5o. Narrow-band filters centered on 0.9536, 1.1298, 1.606, 1.8986 and 2.1641 \mu m and medium-band filters on 1.4556 and 2.2181 \mu m were used. For each filter, full rotational coverage was obtained, with increments of ~ 20o of longitude.
The resulting 144 frames were initially reduced with CALNICA and then PSF-calibrated with the Iterative Blind Deconvolution algorithm. This algorithm, coded on the program IDAC, performs PSF deconvolution through the physically constrained iterative minimization of an error metric. The high signal-to-noise of the data allowed us to achieve super-resolution.
Here we compare the first results of the deconvolution with previous results on the surface mineralogy of 4 Vesta. Further developments of this work will lead to the first mineralogical map of 4 Vesta on the 0.95-2.2\mu m range.
J. Carvano was supported by a CNPq fellowship.