holy cosmic dust Batman!!! nice result Stuart, my only pathetic suggestion from an armchair wannabe is to crop out the right hand side and leave the comet and glob - they are brilliant
When I acquire the images I use a sequence of two minute L, R, G and B, then repeat. This gives at least a six minute (but typically 8 to 9 minute) gap between like exposures. Then you align as per normal on the stars, sigma reject and combine, which basically eliminates the comet and leaves you with the star field. The same process for all the LRGB subsets and combine these to form the colour image of the star field.
Next you do the same for the comet, i.e. one star align on the comet, the normal sigma rejection will remove most of the star field and leave the comet. In this case there was a lot of 47Tuc still remaining. Then align the R, G, B and L, frames and combine to form the colour image.
Next take the two colour images into photoshop, layer the comet over the star field apply a layer mask and cut out the bit over the comet, then blur the layer mask about 50 pixel Gaussian.
Job done.
I can post the intermediate frames if this helps...
