AAS 201st Meeting, January, 2003
Session 91. Computational Techniques and Tools
Poster, Wednesday, January 8, 2003, 9:20am-6:30pm, Exhibit Hall AB

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[91.09] Flatfield Correction by Differential CCD Photometry in M 67

R. P. Boyle (Vatican Obs.), V. Laugalys (ITPA, Vilnius), A.G.D. Philip (Union College and ISO)

To remove instrumental effects in CCD stellar photometry, they must first be measured in the telescope-camera optical system. The flatfield exposure is the image measurement to the input of unit illumination over the field of view (FoV). To the extent that the assumption of input of uniform illumination is compromised by any added off-axis scattered light, then there results an error of the flat (EoF) to not having constant zero-point scale in the stellar photometry. To learn the EoF certain exposures need be made on a rich stellar field, like the open cluster M 67. By offset pointing about 1/3 FOV and offset rotation of the camera to make multiple exposures on M 67, the differential photometry in the instrumental system alone can reveal the EoF, i.e., what difference it makes, if any, on where the stars fall in the FoV. An illumination correction extracted from the differential photometry, provided well enough sampled, can then be applied to the offending flat.

The author(s) of this abstract have provided an email address for comments about the abstract: rboyle@as.arizona.edu

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