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My M67 photometry results
Hi everyone,
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.
-Mike Durkin
Thanks Brian, My values ranged from -0.080 to -0.110, with an average of -0.094 and a standard deviation of 0.011. That agrees with previous calculations, which would typically be around -0.09. -Mike Durkin
Hi! That sound like an interesting experiment indeed! Do you happen to have an image of the star field / or even a screenshot of the analysis with the stars marked :-) , just to give a visual impression? Or a chart you used to identify the stars. I have a feeling I would not be able to replicate this with a F/5 , 6 " Newtonian, I guess, as it might be difficult to find enough space to place the photometry aperture around individual stars.
CS HB
Iused the following image to identify the stars: http://binaries.boulder.swri.edu/binaries/fields/m67.html There's a link on that page to the photometry data that Arne obtained around 2000. My own setup was an 8 inch at f/10, so I also have a feeling you might have some trouble with a 6 inch, f/5. I wonder if you could use a barlow to get a smaller field of view? -Mike Durkin
Hi! Excellent, exactly what I was looking for. Yes, I could try with a Barlow. Hmm... I've done photometry on a Mira down to 11 mag already with the 6" and DSLR, this could be a nice challenge :-). Thanks again HB
Hi Mike, Your results look really good. Congratulations! What type of variation in the transformation coefficient did you have? Brian