Koch, Andreas and Odenkirchen, Michael and Grebel, E.K. and Caldwell, John A. R. (2003) A calibration map for Wide Field Imager photometry. Astronomical Notes / Astronomische Nachrichten, 325 (4). pp. 299-306. ISSN 0004-6337
Full text not available from this repository.Abstract
We present a prescription to correct large-scale intensity variations affecting imaging data taken with the Wide Field Imager (WFI) at the MPG/ESO 2.2 m telescope at the European Southern Observatory at La Silla in Chile. Such smoothly varying, large-scale gradients are primarily caused by non-uniform illumination due to stray light, which cannot be removed using standard flatfield procedures. By comparing our observations to the well-calibrated, homogeneous multicolour photometry from the Sloan Digital Sky Survey we characterise the intensity gradients across the camera by secondorder polynomials. The application of these polynomials to our data removes the gradients and reduces the overall scatter.We also demonstrate that applying our correction to an independent WFI dataset significantly reduces its large-scale variations, indicating that our prescription provides a generally valid and simple tool for calibrating WFI photometry.