Abell 20 is an extremely faint planetary nebula with a dim, and quite blue, central star.
In February 2000, Brian Skiff contacted the observatory and indicated that VIZIER cited several positions for this central star which varied by a few arcseconds. We performed astrometry against the USNO A2 in six images, using approximately 500 stars in our plate solutions, which allowed us to utilize a distortion model. Note the variation in the x,y coordinates of the star in the images we measured (as indicated in the results, below); this deliberate offset is designed to reveal systematic trends in the astrometry. In addition, notice the star to the northwest (upper right) of our central star target - we had to use a small aperture size to avoid contamination from that star.
The measurements we made have been used to update the SIMBAD database.
The six images were taken by Acquire 13 beta (for ACP2), available on the RoboticObservatory home page.
Epoch: 01 Mar 2002 [0] RA=07h22m57.677s Dec=01°45'33.89" X=97.234 Y=34.673 Flux=16898 [1] RA=07h22m57.687s Dec=01°45'33.96" X=78.936 Y=65.835 Flux=15248 [2] RA=07h22m57.688s Dec=01°45'33.91" X=199.931 Y=280.597 Flux=15172 [3] RA=07h22m57.686s Dec=01°45'33.95" X=188.857 Y=292.390 Flux=15248 [4] RA=07h22m57.685s Dec=01°45'33.96" X=254.559 Y=167.782 Flux=16898 [5] RA=07h22m57.683s Dec=01°45'33.96" X=440.634 Y=274.470 Flux=15248