Checks on photometry

Checks are performed on the photometry to make sure that the photometry in the catalogs generated from the stacked images agrees with 2MASS and to ensure that the photometry is self-consistent bteween WIRwolf stacks.

The catalogs for each image stack were compared to 2MASS. As noted before, only the faintest 2MASS are unsaturated in WIRcam images, so the comparisons are necessarily noisy, with a typical scatter of 0.2 mags. The plot below shows an better than average

Example of a comparison between 2MASS and WIRwolf

However the average offsets between 2MASS and WIRwolf stacks are typically good to about 0.02 mags, as shown by the plot below.

Photometric zero-point differences between WIRwolf and 2MASS

Many WIRwolf stacks overlap nearby stacks. The catalogs from these stacks were compared and the photometric residuals measured to determine the zero-point differences. The results are shown below. Not ethat only a very few H-band images overlap with neighbour H-band iamges. The results for H-band are not plotted. The typical zero-point error would appear to be about 2%, consistent with the residuals with respect to 2MASS.

Photometric zero-point differences between adjacent WIRwolf stacks

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