The OmegaCAM photometric systems

OmegaCAM calibration plan (1) Basic OmegaCAM terminology : ● Key bands vs User bands ● Key band -> User band transformation tables ● Monolithic filters and calibration filter ● Polar field and equatorial fields ● Monitoring

OmegaCAM calibration plan (2)

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 OmegaCAM calibration plan (3)

OmegaCAM photometric standard stars Standard fields used for daily calibration : ● field centered on south celestial pole (polar field) ● eight equatorial fields : Available photometric bands : u', g', r', i' SA 92, SA 95, SA 98, SA 101, SA104, SA 107, SA 110, SA113

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

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 : ~ candidate secondary standards covering a FoV of 1.1deg X 1.1deg

Monitoring the quality of the night Standard extinction coefficients adopted : u' = 0.47 r' = 0.09 g' = 0.19 i' = 0.05 OmegaCAM photometric standard stars : INT/La Palma preparatory program (2)

Color terms : u' : none detected g' : / r' : none detected i' : / OmegaCAM photometric standard stars : INT/La Palma preparatory program (3)

Zeropoints : / (1) / (2) / (3) / (4) / (1) / (2) / (3) / (4) / (1) / (2) / (3) / (4) / (1) / (2) / (3) / (4) OmegaCAM photometric standard stars : INT/La Palma preparatory program (3) u' : g' : r' : i' :

OmegaCAM photometric standard stars : INT/La Palma preparatory program (5) Comparing the photometric solution with an independent field

OmegaCAM photometric pipeline (1) : top-level recipes Top-level recipes of the photometric pipeline : ● PhotCalExtractResulttable --> deriving catalogs ● PhotCalExtractZeropoint --> deriving zeropoints ● PhotCalMonitoring --> monitoring ● IlluminationCorrectionVerify ● IlluminationCorrection

OmegaCAM photometric pipeline (2) : photometric catalog photcat = PhotSrcCatalog() photcat.astrom_params = astrom photcat.frame = frame photcat.refcat = refcat photcat.make() photcat.inspect() Photometric pipeline works with catalogs Making these catalogs is always the first processing step in the photometric pipeline

OmegaCAM photometric pipeline (3) : extinction + zeropoint photom = PhotometricParameters() photom.extinct = extinct photom.photcat = photcat photom.make() photom.inspect() Last processing step in photometric pipeline Extinction derived earlier in one of many ways End result used in image pipeline

OmegaCAM photometric pipeline (4) : illumination correction Verification of the presence of sky concentration effects Verification of a WFI image observed in filter #844 plot = create_plot('IllumVerify') plot.show(photcats) Plot shows the variation of the zeropoint as a function of its position on the detector block

OmegaCAM photometric pipeline (5) : illumination correction Characterising the sky concentration effect illum = IlluminationCorrection() illum.photcats = photcats illum.make() illum.inspect()

OmegaCAM photometric pipeline (6) : illumination correction The eight illumination correction frames for WFI filter #844 Peak to peak variation : 0.94 – 1.03 image = Image('MEF.fits') image.frames = frames image.make() f = IlluminationCorrectionFrame() f.illum = illum f.chip = chip f.make()

OmegaCAM photometric systems : resources ● “OmegaCAM Data Flow System – users and programmers manual V2.11” ● “OmegaCAM Secondary Standards preparatory programme – progress report” ●