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:

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. The small number of points shown in the blue position are generally found near NAN/masked regions, or for stars with NANs in the core (saturated?). However, the other two positions have these objects in regions that can be clearly seen to be the "interchip gaps" of one of the input pointings.

Red:

ID	FWHM	AIRM	ZPT	WEIGHT	COVAR	MEDIAN	CHISQ	ADDV
4	3.54	1.50	24.51	3.95e-03	nan	nan	12.59	10.35	o6015g0231o
5	3.63	1.47	24.51	3.72e-03	nan	nan	19.15	16.54	o6015g0212o
0	5.66	1.49	24.55	1.55e-03	nan	nan	8.51	7.15	o5662g0217o
2	6.05	1.51	24.55	1.39e-03	nan	nan	37.53	30.78	o5662g0234o
3	6.27	1.50	24.54	1.03e-03	nan	nan	21.12	17.20	o5272g0175o
1	6.41	1.48	24.54	9.08e-04	nan	nan	31.59	27.03	o5272g0191o

Green:

ID	FWHM	AIRM	ZPT	WEIGHT	COVAR	MEDIAN	CHISQ	ADDV
12	4.12	1.67	24.50	7.10e-04	nan	nan	1731.85	1398.38	o6015g0200o
11	4.18	1.75	24.49	7.64e-04	nan	nan	1989.35	1687.85	o6015g0182o
6	6.04	1.52	24.55	4.67e-04	nan	nan	1173.88	1000.39	o6057g0176o
4	7.00	1.49	24.56	3.30e-04	nan	nan	260.76	225.22	o6057g0161o
13	7.24	1.48	24.58	3.20e-04	nan	nan	1401.73	1188.33	o5649g0261o
0	7.36	1.54	24.56	1.57e-04	nan	nan	68.16	58.80	o5280g0239o
10	7.52	1.49	24.54	nan	nan	nan	nan	nan	o5292g0215o
7	7.64	1.48	24.58	nan	nan	nan	nan	nan	o5649g0244o
1	7.73	1.52	24.56	nan	nan	nan	nan	nan	o5280g0252o
2	7.80	1.51	24.55	nan	nan	nan	nan	nan	o6057g0156o
9	7.96	1.48	24.49	nan	nan	nan	nan	nan	o5292g0200o
8	8.37	1.53	24.56	nan	nan	nan	nan	nan	o5280g0241o
3	8.81	1.51	24.57	nan	nan	nan	nan	nan	o5280g0254o
5	9.30	1.49	24.56	nan	nan	nan	nan	nan	o6057g0143o

Blue:

ID	FWHM	AIRM	ZPT	WEIGHT	COVAR	MEDIAN	CHISQ	ADDV
9	4.53	1.49	23.11	8.00e-06	nan	nan	8283.31	7494.13	o6021g0287o
8	5.57	1.47	24.54	3.16e-04	nan	nan	1083.10	913.54	o6021g0270o
3	6.84	1.50	24.57	7.35e-04	nan	nan	2037.23	1540.00	o5649g0254o
7	7.02	1.48	24.55	4.28e-04	nan	nan	2910.72	2455.73	o6057g0175o
6	7.48	1.49	24.55	3.52e-04	nan	nan	3202.65	2723.26	o6057g0155o
2	7.55	1.53	24.53	nan	nan	nan	nan	nan	o6013g0350o
0	7.71	1.60	24.55	nan	nan	nan	nan	nan	o5280g0244o
1	8.06	1.57	24.56	nan	nan	nan	nan	nan	o5280g0257o
4	8.36	1.56	24.53	nan	nan	nan	nan	nan	o6013g0366o
5	8.42	1.50	24.57	nan	nan	nan	nan	nan	o5649g0271o

Pre 2013-03-07