Astrometry of the PF-QHY Images

Based on the recent tests, the quality of the new prime focus corrector appears excellent. The following plot shows the field distortion based on 3 images (TWFC1-0000041754, 55 and 56) taken with binning 4x4 during the night 20210320, which were resolved with THELI 2.13 using Scamp based on the SDSS-DR9 star catalog.



Although the distortion pattern looks circular, the differences in pixel scales between the centre and the corners are below 0.0001 arcsec, thus the field of the camera could be considered flat with a scale of 0.2668 arcsec/pixel (binning 4x4).

Currently the following astrometric constants are missing from the headers: CRVAL1, CRVAL2, CRPIX1, CRPIX2, CUNIT1, CUNIT2, CD1_1, CD1_2, CD2_1, CD2_2 and should be inserted for astrometric projects. The RA and DEC values are accurate, representing the tracked position ICRS J2000 of the observed target.