One of my Fall projects is to get serious with variable star photometry with my Seestar S50. It has been suggested to me that perhaps one of the most important things I can do is concentrate on a Landolt field and work to devise an acquisition and processing workflow that results as good as 0.05 mag measurement of Landolt stars.
I want to submit good data and I think that exercise will help tremendously in me getting there.
The challenge for me is, there are a lot of Landolt fields: Standard Fields
Some of these fields are quite crowded and I’m unsure what makes a good candidate Landolt field for my S50 (both in terms of star density and magnitude). The S50’s field of view is about 1.3x0.7 degrees.
What am I looking for? (And if you can suggest one or two fields, that would be delightful. I’m in the northern hemisphere around 30 degrees N latitude.)
I’ve got a Seestar S50 and I did my transformation coefficients using several Landolt fields. I’m at 41 degrees north so I went though the list of standard fields here Standard Fields and picked the ones at +45 degrees which go almost directly overhead for me. I would avoid M67 and NGC 7790. They are too crowded for the S50’s short focal length.
It helped me greatly to put the S50’s field of view into a planetarium program (I use Guide 9.0) to visualize what the instrument can see. Then look for fields that have a wide range of B-V values bright enough to get good signal to noise ratios. Things get dicey fainter than 12.5 or 13.0 with a 45 second exposure for me with the S50 properly defocused to spread the image over several pixels in order to illuminate the Bayer matrix properly. I did mine imaging over 8 clear nights in late winter and early spring. I used SA 23, 26, 29 SF5, 32 and 35. I picked these because they transited during nights that were clear with no moon. I took 10 to 20 images of each field on the nights that they were available.
I used NINA to image the fields and took a good many flat fields and many dark frames each night to properly calibrate the images. I calibrated and debayered the images in ASTAP and then did the photometry.
At this time of year, SA 41 looks like it transits around midnight DST. SA 38 transits around 9:30 DST. SA 20 transits around 3:30 am DST. These will get an hour earlier every 2 weeks.