[Comm2011] OCAM secondary standards

[Edwin A. Valentyn]

Dear Dietrich,

Please find enclosed our first preliminary assessment of the remaining 
work to be done on the OmegaCAM secondary Standard fields

hope this clarifies

kind regards

Edwin Valentijn




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Note on OmegaCAM Secondary standard Programmme- CP req 569.
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The table below lists the 22 SA fields considered for OmegaCAM secondary 
standard fields.  Out of this list 8 field will be selected. The 8 
preceded by an asterisk (*) are those primarily selected for full RA 
coverage as specified in the Calibration Plan.

Those fields with filter list entries in the OCM2 and OCM3 columns have 
been observed during commissioning in the context of Req 569 Secondary 
standards and Req 548 Illumination correction. The OB covers 
approximately 2x2 square degrees by making 32 observations with each CCD 
centered on the specified coordinates.

The number of Landolt standard stars, Stetson standard stars, SDSS DR5 
stars and stars from the Preparatory Programme (PP) for the OmegaCAM 
Secondary Standard Program are listed for the OmegaCAM 1.2 square degree 
fieldsize.


  Field   RA [deg]  Dec [deg]  Land  Stet   SDSS5    PP    OCM2    OCM3
------------------------------------------------------------------------
   SA51   112.663   +29.828      0      0     214      0
   SA57   197.171   +29.384      0      0     952      0
   SA68     4.146   +15.844      0      0    1302      0
  *SA92    13.946    +0.949     41    213    1094   6475          ugrizV
   SA93    28.783    +0.824      4      0    1128      0
   SA94    44.033    +0.571      7      0    1099      0
  *SA95    58.500    +0.000     45    426    1093      0          ugriz
  *SA98   103.021    -0.328     46   1116       0  23840
   SA100  133.529    +0.546      6      1    3343      0
  *SA101  149.112    -0.386     35    117    1776   5591
   SA102  163.779    +0.866      5     66    1517      0
   SA103  178.779    +0.556      2      0    1507      0
  *SA104  190.488    -0.529     34     76    1576   5701
   SA105  204.533    +0.676      4      0    2172      0
   SA106  220.533    +0.427      2     15    2864      0
  *SA107  234.825    -0.263     28    728    3889  12006  grizV
   SA108  248.033    +0.369      6      3    6148      0
  *SA110  280.600    +0.346     39    589       0  38562
   SA112  310.529    +0.524      7     73   12087      0
  *SA113  325.375    +0.499     42    483    4046  13947  ugzB    ugrizBV
   SA114  340.529    +0.689      9      5    1957      0
   SA115  355.779    +0.888     10      0    1170      0

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The data taken in OCM2 and OCM3 are currently being investigated. 
Preliminary indications are that OCM2 data may not be usable due to 
telescope re-configuration and/or observing conditions. We expect to 
have obtained  a reasonable set for the fields SA 92, 95 and 113.

The OmegaCAM Calibration Plan indicates two nights bright time  each 
month during the first year after commissioning.

Now, reviewing this after our experiences and progress with the various 
commissioning runs the following has to be taken into account:

i) it takes about 8h- one night to do one field in all required bands 
(u,g,r,i,z,B,V)
ii) likely we will have 2-3 fields well covered by the commissioning runs
iii) the analysis work related to this programme is more complex than 
expected due to very large illumination corrections detected for the 
interference filters, up to 15%. This aspect requires more cross checks 
with redundant observations, particularly due to the noted dependency of 
the correction on the rotator position. We are still analysing the data 
and reviewing the approach (eg more elaborate usage of dome flats).

Adding the pluses and minus of the above, and taking bad weather into 
account it seems reasonable to schedule 2 bright nights each full moon, 
occasionally skipping ( eg august 2011) one full moon period in order to 
smear out the remaining fields over an 8 month period.

In the end this involves some relaxing of the original requirement, 
which is good, but this can only be confirmed after we have settled the 
procedures to accurately face the illumination corrections.

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