The OmegaCAM photometric systems

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The OmegaCAM photometric systems
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OmegaCAM calibration plan (1)
Basic OmegaCAM terminology

• Key bands vs User bands
• Key band -gt User band transformation tables
• Monolithic filters and calibration filter
• Polar field and equatorial fields
• Monitoring

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OmegaCAM calibration plan (2)
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OmegaCAM calibration plan (3)
Important considerations

• OmegaCAM is continuously maintained in the
• Key bands ( u', g', r', i' )
• standard fields only observed in User bands if
• the science programme of the night warrants it
• photometric calibration is done per-chip

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OmegaCAM photometric standard stars
Standard fields used for daily calibration

• field centered on south celestial pole (polar
  field)
• eight equatorial fields

SA 92, SA 95, SA 98, SA 101, SA104,
SA 107, SA 110, SA113
Available photometric bands u', g', r', i'
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OmegaCAM photometric standard stars preparatory
programs
Establishing photometric standards

• INT Secondary Standards Preparatory Programme
• OmegaCAM Secondary Standards Programme

Photometric standards presently available

• classisal Landolt catalog
• stars from Sloan Digital Sky Survey
• new candidate Sloan standards for SA 98

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OmegaCAM photometric standard stars INT/La
Palma preparatory program (1)
Establishing photometric standards for SA 98

• data was processed with the Astro-Wise system
• photometric transformation coefficients
  determined
• using Sloan standards
• no illumination correction was required for INT

Results 23.000 candidate secondary standards
covering a
FoV of 1.1deg X 1.1deg
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OmegaCAM photometric standard stars INT/La
Palma preparatory program (2)
Monitoring the quality of the night
Standard extinction coefficients adopted
u' 0.47 r' 0.09 g' 0.19 i' 0.05
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OmegaCAM photometric standard stars INT/La
Palma preparatory program (3)
Color terms
u' none detected g' 0.14 /- 0.01 r' none
detected i' 0.07 /- 0.01
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OmegaCAM photometric standard stars INT/La
Palma preparatory program (3)
Zeropoints
u'
23.725 /- 0.019 (1) 23.772 /- 0.019 (2) 23.575
/- 0.039 (3) 23.542 /- 0.029 (4) 24.939 /-
0.016 (1) 25.064 /- 0.005 (2) 25.091 /- 0.008
(3) 25.122 /- 0.004 (4) 24.579 /- 0.015
(1) 24.702 /- 0.010 (2) 24.806 /- 0.009
(3) 24.803 /- 0.010 (4) 24.126 /- 0.018
(1) 24.255 /- 0.012 (2) 24.412 /- 0.011
(3) 24.413 /- 0.007 (4)
g'
r'
i'
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OmegaCAM photometric standard stars INT/La
Palma preparatory program (5)
Comparing the photometric solution with an
independent field
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OmegaCAM photometric pipeline (1) top-level
recipes
Top-level recipes of the photometric pipeline

• PhotCalExtractResulttable --gt deriving catalogs
• PhotCalExtractZeropoint --gt deriving zeropoints
• PhotCalMonitoring --gt monitoring
• IlluminationCorrectionVerify
• IlluminationCorrection

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OmegaCAM photometric pipeline (2) photometric
catalog
Photometric pipeline works with catalogs
Making these catalogs is always the first
processing step in the photometric pipeline
photcat PhotSrcCatalog() photcat.astrom_params
astrom photcat.frame frame photcat.refcat
refcat photcat.make() photcat.inspect()
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OmegaCAM photometric pipeline (3) extinction
zeropoint
Last processing step in photometric pipeline
Extinction derived earlier in one of many ways
End result used in image pipeline
photom PhotometricParameters() photom.extinct
extinct photom.photcat photcat
photom.make() photom.inspect()
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OmegaCAM photometric pipeline (4) illumination
correction
Verification of the presence of sky concentration
effects
Plot shows the variation of the zeropoint as a
function of its position on the detector block
plot create_plot('IllumVerify')
plot.show(photcats)
Verification of a WFI image observed in filter
844
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OmegaCAM photometric pipeline (5) illumination
correction
Characterising the sky concentration effect
illum IlluminationCorrection() illum.photcats
photcats illum.make() illum.inspect()
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OmegaCAM photometric pipeline (6) illumination
correction
Peak to peak variation
0.94 1.03
f IlluminationCorrectionFrame() f.illum
illum f.chip chip f.make()
image Image('MEF.fits') image.frames
frames image.make()
The eight illumination correction frames for WFI
filter 844
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OmegaCAM photometric systems resources

• OmegaCAM Data Flow System users and
  
• programmers manual V2.11
• OmegaCAM Secondary Standards
• preparatory programme progress report
• http//portal.astro-wise.org/