= Stacking Photometry Issue =

== 2013-03-07 ==

After some reading through email threads and looking at Eddie's figures, I constructed a similar test/data set.  I chose three i-filter stacks along an RA slice at dec = -27, and compared the CAL_PSF_MAG values calculated by the static sky CMF to the median value of CAL_PSF_MAG for those objects in the warp CMFs.  This nicely reproduced the figure that Eddie had made.  The three positions I chose were (RA,DEC,stack_id) red=(170,-27,1111371), green=(197,-27,1157219), blue=(200,-27,1238704).  Based on Eddie's ucal comp figure (reproduced below), the red and green positions sample the area that is mottled with large offsets, and the blue position is a "good" position where the offsets seem small.  Constructing the <m_W> - m_SS plot shows that the blue position is good, with a single population scattered around zero:

[[Image(warp_SS_diff.png,800px)]]

Based on this figure, I selected the objects with m_SS < 20 AND (<m_W> - m_SS) < -0.25 to isolate the offset magnitudes, and then plotted them on the images:

Red: 

[[Image(overlay_1111371.jpg,600px)]]

Green:

[[Image(overlay_1157219.jpg,600px)]]

Blue:

[[Image(overlay_1238704.jpg,600px)]]

== Pre 2013-03-07 ==

[[Image(ps1stackucalcomphr.png,800px)]]