Mark,
Thanks for writing that up. It is good to see different approaches.
You are using an elliptical aperture which I don’t think is correct and probably explains the slightly brighter magnitude that you are getting since you will have included some of the dust tail. Comphot always uses a circular aperture which is reasonable since the comet’s coma is likely to be spherical and the rules are that you should not include the tail in the estimate. Also, how do you exclude stars that appear in the aperture? The sigma-clipped comet stack does significantly attenuate stars but they are not completely removed.
You make the comment that you would not normally use this approach with ASTAP. How would you normally deal with the fact that the comet is moving relative to the background since stacking over long periods is often necessary to get sufficient SNR in the outer coma?
Nick.
PS for Grant – Surely your home-brew camera software can query the mount’s commanded pointing position from SkyX and then insert the required FITS keywords. Blind solving is great but it is relatively slow so it is always best to have this data in the header. In particular Astrometrica is a bit of a pain to use if this is not there.