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## Conclusions

Two problem areas were identified, namely the last part of night 4, and night 9. Conclusions:
Night 4

• Clearly, field 210 in both GR and JB are non-photometric.
• The offsets between field 33 night 1 and field 33 night 4 of -0.01 in GR and -0.02 in JB are well determined. Field 33 night 1 were taken to be photometric, and field 33 night 4 were taken to be non-photometric by the above amounts.
• The rest of the night 4 checked fields, 26, 2410.1, 427, 215, and 28, have nominal offsets no larger than 0.02. These offsets are not determined better than that, so they were all taken to be zero.

That the accuracy of these offsets are 0.01-0.02 can be seen from the field 210 complex offsets diagrams, Figure . Different paths from one field to another give results that differ by up to 0.03.

• The adopted value of the offset for field 210 were taken as a suitable mean to be -0.10 in GR and -0.11 in JB.
Night 9

• Field 00 was taken to be the reference image, since it was the one most likely to be photometric, because it had been observed first.
• The offsets for field 14, 15, and 13 were taken to be the derived offset with field 00, namely +0.03, -0.04, and -0.06, respectively. The derived offset between field 13 and 15 is very consistent with these other offsets, the difference is only 0.01, which is less than the uncertainty of the offsets.
• That the field 00 - field 14 offset is positive means that field 14 is a better photometric reference than field 00. However, since no standard stars were observed on night 9 and hence no night coefficient is available, we will need to determine the zero point using comparison with external references anyway.
• Field 18, observed just after field 15, did not overlap with any of the other 4 fields. Since it was believed that it was observed under non-photometric conditions, it was assigned an offset equal to that of field 15, namely -0.06.
Other nights

• Field 16 night 1 and field 16 night 6 were both believed to be photometric. The nevertheless non-zero offsets between them of 0.01 in GR and 0.02 in JB10.2 were taken to be the typical internal photometric uncertainties. No offsets should be applied to either of these images.
The correcting offsets derived above are listed in Table . These offsets (where non-zero) were added to the 4 magnitude quantities, , , , and .

Table: List of Non-photometric Corrections
 Night Offset Field Pair Program galaxies GR JB 1 00 x R245, R253, R255, R256, R266, R268, R269, R273, R286, R293 1 0.00 0.00 16 x R308 1 13 x R209, R217, R234, R237, R241 1 25 - 1 37 x R166, R185 1 0.00 0.00 18 x R214, R219, R225 1 12 x R255, R273, R278 1 21 - 1 0.00 0.00 33 x R317 1 45 - 2 214 R261 2 320 R327 2 0.00 0.00 428 R250 2 632 - 2 29 R193 2 419 R138 2 519 R129 2 15 x R213, R216, R224, R226, R239, R245 3 00 x R245, R253, R255, R256, R266, R268, R269, R273, R286, R293 3 0.00 0.00 14 R316, R322 3 15 x R213, R216, R224, R226, R239, R245 3 13 x R209, R217, R234, R237, R241 3 27 x R188, R194, R209 3 23 x R243 3 43 R338, R343, R347 3 18 x R214, R219, R225 3 321 R283, R288 3 535 R252, R295 3 35 R218, R231 4 46 R238 4 47 R202 4 34 R254 4 22 R319 4 0.00 0.00 26 R334, R359 4 24 x R211, R212, R243 4 -0.10 -0.11 210 x R336, R337 4 0.00 0.00 427 R305 4 0.00 0.00 215 x R225 4 0.00 0.00 28 x R336, R337, R340 4 -0.01 -0.02 33 x R317 6 213 - 6 39 x R166 6 36 - 6 44 - 6 45 - 6 32 - 6 64 R389 6 66 R307 6 615 R112, R120 6 0.00 0.00 16 x R308 6 21 - JU 9 0.00 00 x R239, R245, R253, R255, R256, R266, R268, R269, R273, R286, R293 9 +0.03 14 R316, R322 9 -0.04 15 x R213, R216, R224, R239, R245 9 -0.06 13 R217, R234, R237 9 -0.06 18 R214, R219, R225

Notes: The list is in chronological order. Exactly those images that appear in the offset plots in this section has a listed offset (with the exception of field 18 JU; see the text). Pair'' means that the given entry has one or more galaxies that have been observed more than once. The 64 galaxies in this table are the ones in the HydraI surface photometry sample, cf. Table  (p. ).

Next: 11. The Standard Calibration Up: 10.3 Corrections to Non-Photometric Previous: The 5 JU fields

Properties of E and S0 Galaxies in the Clusters HydraI and Coma
Master's Thesis, University of Copenhagen, July 1997

Bo Milvang-Jensen (milvang@astro.ku.dk)