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Abstract: The monochromatic illumination system is constructed to carry out in situmeasurements of the response function of the mosaicked CCD imager used in theSloan Digital Sky Survey SDSS. The system is outlined and the results of themeasurements, mostly during the first 6 years of the SDSS, are described. Wepresent the reference response functions for the five colour passbands derivedfrom these measurements, and discuss column to column variations and variationsin time, and also their effects on photometry. We also discuss the effectarising from various, slightly different response functions of the associateddetector systems that were used to give SDSS photometry. We show that thecalibration procedures of SDSS remove these variations reasonably well with theresulting final errors from variant response functions being unlikely to belarger than 0.01 mag for g, r, i, and z bands over the entire duration of thesurvey. The considerable aging effect is uncovered in the u band, the responsefunction showing a 30% decrease in the throughput in the short wavelength sideduring the survey years, which potentially causes a systematic error inphotometry. The aging effect is consistent with variation of the instrumentalsensitivity in u-band, which is calibrated out. The expected colour variationis consistent with measured colour variation in the catalog of repeatedphotometry. The colour variation is delta u-g ~ 0.01 for most stars, and atmost delta u-g ~ 0.02 mag for those with extreme colours. We verified in thefinal catalogue that no systematic variations in excess of 0.01 mag aredetected in the photometry which can be ascribed to aging and-or seasonaleffects except for the secular u-g colour variation for stars with extremecolours.

Autor: Mamoru Doi, Masayuki Tanaka, Masataka Fukugita, James E. Gunn, Naoki Yasuda, Zeljko Ivezic, Jon Brinkmann, Ernst de Haars, Scott



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