My M67 photometry results
I've come across a couple of references that mention using M67 for calibration since there's accurate photometry data for that cluster. So a couple of weeks ago, I hooked up my DSLR to my 8 inch SCT and took some images of M67, and I'd like to share my results.
I'm attaching a spreadheet which lists my results. I stacked 30 light frames in groups of 5 to create a series of 6 FITS files. I then measured the magnitude of various stars in the images and used. I also used Brian Kloppenborg's spreadsheet to calculate the color transformation coefficient. I didn't calculate the extinction coefficient since the field of view was small.
I'm reasonably happy with my results. My average measured V magnitude values are all with 0.02 of the published values. I noticed a correlation between the standard deviation of my measurements and the magnitude of each star, which also seems reasonable. For a magnitude 10.02 star, I have a standard devation of 0.004. For a magnitude 12.25 star, I have a standard devation of 0.025. I didn't measure stars fainter than that because according to the software program I was using (MaxDLSR), a star that was 12.25 had a SNR that was just over 100.
I was a little disappointed that I had more variation in the the values for the color transformation coefficient that I was expecting.
Please take a look at my results and let me know what you think.