ISSA Explanatory Supplement
IV. ANALYSIS RESULTS
B. Positional Accuracy

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Positional accuracy and small source photometric consistency were studied using point sources selected from the IRAS Point Source Catalog to be bright enough to measure easily in the ISSA data and to be free of interference from extended emission or nearby point sources. Point sources at 12 and 25 µm were selected to be at high Galactic latitude, |b|>30°, with brightness between 5 and 55 Jy and correlation coefficients of 0.99 or greater. The 23 sources at 12 µm and 24 sources at 25 µm are listed in Table IV.B.1. Point sources at 60 and 100 µm were selected from the IRAS galaxy list (Soifer et al., 1987) to have a large radial velocity (>4000 km s^-1) with brightness between 5 and 55 Jy. The velocity criterion is designed to select small angular diameter galaxies unlikely to be extended at the resolution of the ISSA maps. The 14 sources at 60 µm and 15 sources at 100 µm are listed in Table IV.B.1.

Table IV.B.1 Point Sources Used in the Position and Photometric Analyses

12 µm		25 µm		60 µm		100 µm
IRAS Name	Field	IRAS Name	Field	IRAS Name	Field	IRAS Name	Field
00515-6308	25	00515-6308	25	00163-1039	162*	00163-1039	162*
01452-8026	3	01452-8026	3	02228-2500	{1}98	02228-2500	{1}98
02039-5722	26	02039-5722	26	04315-0840	169*	04315-0840	169*
02110-7143	11	02110-7143	11	04461-0624	169*	04461-0624	169*
02238-5947	26	02238-5947	26	05189-2524	135	05189-2524	135
03040-8013	3	03040-8013	3	08354+2555	316*	09320+6134	397
03336-7636	3	03336-7636	3	09320+6134	397	09437+0317	213*
05150-4056	73	04330-6307	28	10565+2448	319*	10565+2448	319*
05174-3345	102	05150-4056	73	12540+5708	399	12540+5708	399
05217-3943	73	05174-3345	102	12590+2934	322*	12590+2934	322*
05345-4406	73	05217-3943	73	13136+6223	399	13136+6223	399
10416+6740	414	05345-4406	73	13136+6223	400	13136+6223	400
10521+7208	414	10416+6740	414	13183+3423	322*	13183+3423	322*
11284+6936	415	10521+7208	414	23488+2018	270*	23488+2018	270*
15448+3828	355	11284+6936	415	23591+2312	270*	23591+2312	270*
15566+3609	355	15448+3828	355
16164+5952	402	15566+3609	355
16342+6034	402	16164+5952	402
17126+3625	357	16342+6034	402
17133+3651	357	17126+3625	357
17329+5359	383	17133+3651	357
17403+6234	403	17329+5359	383
		17403+6234	403
		20427-8243	9

^*These fields are from the || < 50° sky.

Figure IV.B.1(a) Histograms of Position Differences in RA Between PSC and ISSA larger largest

The position accuracy analysis consisted of comparing the apparent position of the selected sources in the ISSA maps with the published source locations in the IRAS Point Source Catalog. The ISSA position was taken to be the photocenter of the source in the ISSA map. Photocenters were obtained by producing a flux-weighted average of the pixel positions over a circular region surrounding a source after subtraction of a local background. Figures IV.B.1(a) and IV.B.1(b) display histograms of difference between the PSC position and the ISSA position for the selected point sources. Table IV.B.2 summarizes the statistics obtained from the histograms. The mean position differences between the PSC and ISSA are less than 0.1 pixel (9") and the expected position uncertainty of a single source is less than 0.2 pixel (18").

Figure IV.B.1(b) Histograms of Position Differences in DEC Between PSC and ISSA larger largest

Table IV.B.2 ISSA and ISSA Reject Fields Affected by Saturated Data

	12 µm	25 µm	60 µm	100 µm
# of Sources	23	24	14	15
Mean Delta R.A. (')	0.004	0.001	0.040	0.031
sigma(Delta R.A.) (')	0.156	0.267	0.179	0.224
Mean Delta Dec. (')	0.070	0.034	-0.078	-0.131
sigma(Delta Dec.) (')	0.126	0.225	0.156	0.236

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