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Project Progress

On October 23 2007, Comet 17P/Holmes abruptly brightened by a factor of a million, from 17^th to 3^rd magnitude, in an apparent abrupt outburst of material. We have applied image enhancement techniques to show that the ejected material includes discrete lumps thrown in many directions. Also, we have developed a novel modeling approach that combines dust with dust-emitting fragments, and we are using it to constrain the nature of Holmes’ eruption.

After 17P/Holmes erupted, Hawaii graduate student Rachel Stevenson acquired a unsurpassed data set consisting of UH 88” images, followed later by very large field CFHT images as the eruption expanded.

Using Laplacian filter image enhancement and median radial profile subtraction, we removed most of the smooth, symmetric dust coma, leaving only asymmetric eruption features. By identifying these features across a series of observing nights, we saw a pattern of lumps, moving radially outward from the nucleus. We believe that these are icy chunks, emitting dust as they sublimate. When we trace the motion of these chunks back in time, we find that they converge closest at the time of the eruption, giving us a consistent picture of a violent outburst of discrete pieces, not just a jet.

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Figure 1 shows our enhanced images of Holmes, with the chunks labeled. Figure 2 shows the extrapolated average distance of the lumps from the nucleus and their common center.

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To model the outburst, we developed a highly flexible code that integrates the motion of a comet, simulating the emission of dust and dust-emitting fragments. Using this code, we are addressing the issues of the direction, shape, and velocity of the eruption, all key to understanding the nature of the phenomenon.

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Figure 3 shows one example of a model run, in which a conical burst of dust-emitting fragments with a 10 to 100 m/s velocity spread is emitted toward the sun, and along the orbit. Snapshots are separated by ten days. The characteristic bending of the dust stream should allow us to disentangle the degeneracies between orbital projection and fragment motion.