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W. H. Ryan, E. V. Ryan, C. T. Martinez (New Mexico Highlands University)
Statistical analysis, spectroscopic studies, and imaging data, all uniquely suggest an impact origin for the Vesta family of asteroids. In order to constrain numerical models of family formation, and uncover the basic principles of asteroid evolution, we have begun a photometric study of 4 Vesta and the asteroids that comprise its family. The collected lightcurves, color data, and subsequent shape analysis, will help to address whether the Vesta chips are intact spall fragments (having a thin, elongated shape) or re-accumulated rubble piles (having roughly spherical, ellipsoidal, or lumpy shapes). The implications of these data will later be examined using an existing numerical hydrocode model (Melosh, et al., 1992) to better understand the family's impact origin. Thus far, we have obtained and reduced lightcurves for 10 of the Vesta-family asteroids using the 1.8-meter Vatican Advanced Technology Telescope (VATT) at the Mount Graham International Observatory. This set of lightcurves has been analyzed to determine asteroid rotation rates, which were found to range from very short (< 3 hours) to > 9 hours. Further, rotationally resolved color data have been collected on approximately 50% of our program asteroids. These data are in the process of being analyzed in order to determine if the Vesta chips appear spectrally homogenous, a possible indication of random, rubble pile reaccumulation, or retain distinct color variations that could be indicative of intact spall fragments.
This work is supported by NASA Planetary Astronomy grant NAG5-8734 and the Vatican Observatory Research Group.
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