Today I received CD-ROM #3. Thank you, Tom. I took a look at some of the images which are all taken with the V filter. For beginning I renamed them:
H3R1260912.fts H3R1260920.fts H3R1260928.fts H3R1260936.fts H3R1260916.fts H3R1260924.fts H3R1260932.fts H3R1260940.fts
I hope it is still clear to which images on CDROM they correspond. I found a match with catalog using fitsblink, after I manually inserted approximate center coordinates and pixel sizes. The current format of WCS coordinates in the header is not complete.
I calculated center coordinates for the images from the above list:
H3R1260912.fts 15:02:31.87 +6:12:09.0 H3R1260916.fts 15:07:44.18 +6:12:08.6 H3R1260920.fts 15:14:20.76 +6:12:09.3 H3R1260924.fts 15:20:33.64 +6:12:09.4 H3R1260928.fts 15:26:50.94 +6:12:09.4 H3R1260932.fts 15:33:08.98 +6:12:10.6 H3R1260936.fts 15:39:09.42 +6:12:11.5 H3R1260940.fts 15:41:55.58 +6:12:07.2
Pixel dimensions are 7.33 arc seconds. Rotation angle is -90.20 degrees.
Here is how WCS keywords should look like to be read by some programs:
CTYPE1 = 'RA---TAN' / Inserted by fitsblink CRVAL1 = 2.28586492404737E+02 / Inserted by fitsblink CRPIX1 = 1.02700000000000E+03 / Inserted by fitsblink CDELT1 = 2.03541013146073E-03 / Inserted by fitsblink CROTA1 = -9.01936682426076E+01 / Inserted by fitsblink CTYPE2 = 'DEC--TAN' / Inserted by fitsblink CRVAL2 = 6.20258131600432E+00 / Inserted by fitsblink CRPIX2 = 1.01850000000000E+03 / Inserted by fitsblink CDELT2 = 2.03518130888765E-03 / Inserted by fitsblink CROTA2 = -9.01936682426076E+01 / Inserted by fitsblink
For such wide a field it is not unusual to have rather poor astrometry without using higher order plate constants. Positional error as a function of distance from the image center is plotted below. It is probably not surprising that the error increases as we go away from the center.
After that I took the image H3R1260928.fts and compared instrumental magnitudes with V magnitudes of stars from the ACT catalog. Appended here is a plot of the magnitude difference between the two as a function of the ACT magnitude.
If you take a look at this image, you will see two outliers. One is right at the edge of field, the other (denoted by arrow), is a star with TYCHO number 36200024501 (zero based image coordinates x=483.09, y=1500.76). It should have a magnitude 7.88, what is apparently not a case here. The star is rather cometary but so are many others which don't have such magnitude differences. In the GSC catalog this star has number 362045 and magnitude 11.24. Must be some variable.
Another interesting thing is a magnitude difference as a function of image coordinate. This is shown below.
Next I made a match with the GSC. There are matches up to magnitude 15.
Unfortunately, I have no time to make some more detailed analysis. It is obvious that flatfielding and dark subtraction will be needed and that everything would be better without coma, but we knew that before. For unprocessed images the magnitude variation in comparison to the ACT catalog is someting like +- 0.16 mag. Limiting magnitude is around 15 for the V filter.