I've compared the 816 processed images from the July 2009 data release to SDSS to get zero points for each image. For y band I fit y_{PS} - z_{SDSS} versus i_{SDSS}-z_{SDSS} and got a slope of -0.247. Using this I made a simulated y-band magnitude for each SDSS star as y_{SDSS-sim} = z_{SDSS}-.247*(i_{SDSS}-z_{SDSS}), assuming that stars of zero i-z color should have zero z-y color. I used the resulting simulated y-band magnitudes to compute the PS zero points.

See PS1_depth for magnitude histograms and zpt_variation_july09 for visual representations of the chip-to-chip zero point variations.

The summary table is:

filter zero point FWHM DRM zero point
g 24.58 ~.06 24.90
r 24.80 ~.06 25.15
i 24.74 ~.05 25.00
z 24.26 ~.05 24.63
y 23.41 ~.05 23.03

I'm just pulling these zero points and FWHM by eye off the following plots, looking for the good photometric clusters of points.

The zero points are well-behaved enough that we can see the effects of atmosphere. We get airmass extinction terms:

filter k_{PS} k_{SDSS}
g .136 .17
r .182 .10
i .122 .06
z .079 .06
y .085 ---

Obviously there is a lot of uncertainty in the values I've given, and I haven't been very careful. However, it is nice to see that they agree vaguely.

The zero points have negligible temperature dependance:

The straight lines through the data are arbitrary lines I've added to make looking for deviations from flatness easier; temperature and zero point look awfully uncorrelated.

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