Photometry with a 114mm

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Grant Privett

 While between OTAs, I have been using my 114mm guidescope and an unfiltered Lodestar to occasionally take some measurements of LL And. Because they were mainly taken on moonlit or partially cloudy nights (and I am a deep sky observer) I just let the camera run a series of 30s frames in the hope it might drive down the errors that would be present with such a small light grasp instrument. Its not the best way to do this sort of thing, but it was simple to do and fun.

To analyse the data, I wrote Python code to plate solve all the frames, locate all the stars, compare the catalogue stars to those on my frames, established the Zp for each frame and thus derive the mag of LL And. I then took the median result (mag1).

To make things more interesting, I also looked at 4 comparison stars from the AAVSO chart and derived mags (mag2) for those using the sums of the fluxes measured from all the frames. I may extend the number of comparison stars.

The results are these:

Date      Mag1   Mag2   Magerr  Frames

210917  13.15   13.32    0.15      122

210918  13.39   13.60    0.4        212

210921  13.71   13.90    0.25      307

210922  13.77   13.98    0.25      277

210929  14.58   14.71    0.35      156

211010  17.41   17.26    0.8        179

Usable results could have been obtained with far fewer frames, but I had hoped to see some evidence of superhump activity (yeah I know) so I just let it run.   

What I am noticing from this – apart from how interesting LL And is – is that the Mag1 value seems consistently brighter than the Mag2 value. I won’t be submitting any observations formally until I figure out what causes that. Has anyone any thoughts on what I might be doing wrong?

EDIT: Andy worked out the problem and I am ashamed that I didn’t myself. One approach used the Gaia g catalogue mag values and the other used the AAVSO sequence mags ie V.