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Correcting spatial gradients: the case of Wide Field Imager photometry

Research output: Contribution to journalJournal article

  • Andreas Koch
  • E. K. Grebel
  • Michael Odenkirchen
  • John A. R. Caldwell
<mark>Journal publication date</mark>2004
<mark>Journal</mark>The Messenger
Number of pages3
Pages (from-to)37-39
Publication StatusPublished
<mark>Original language</mark>English


We present a method to significantly reduce large-scale photometric variations seriously affecting imaging data from the Wide Field Imager (WFI). The primary source for these gradients is non-uniform illumination, which cannot be corrected by standard flatfielding techniques. Comparison of our observations with well-calibrated multi-colour photometry from the SDSS enabled us to characterize and quantify these variations and finally to model them using a second-order polynomial. Application of the model to our observations and an independent dataset consistently reduced the large-scale gradients and thus provides a generally valid and simple tool for improving WFI photometry.