Feb 03-04 2006 Deep Grid Results

Observations - The observations consist of 6 exposures in each of the u*g'r'i'z' filters of Deep Fields D1 and D2. The 6 exposures consist of an unshifted reference image, four dithers shifted southeast, southwest, northeast, and northwest by half a field width, followed by another unshifted image. This shifting places many stars on multiple chips allowing a measure of the chip-to-chip photometric variations, after accounting for exposure-to-exposure variations. The duplicate unshifted image allows an assessment of the photometric conditions during the dither.

Photometry - Photometry was performed with DAOPHOT aperture photometry using 21.5 pixel (4 arcsecond) radius apertures.

Analysis - The analysis proceeded using the same methods used for the photometric grid data.

Results - This analysis produced coefficients (with errors) for each chip and each exposure and are listed below. We also plot the raw input data and the chip-by-chip data and fits. As a check, we also compare the coefficients derived from the three photometry methods by plotting them up with a different symbol for each method (see below). This is probably the best place to look to get an idea of the amount and form of the variations. Considerable structure is visible in the coefficients but with an RMS near or below our error-budget limit of 0.01 mag in both zeropoints and color terms. Nonetheless, as mentioned above, the consistent structure in the zeropoints especially indicate that by tuning Elixir these variations can be removed.