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Paper: High precision stellar photometry
Volume: 8, CCDs in Astronomy
Page: 305
Authors: Penny, A. J.; Buttress, J.; Griffiths, W. K.
Abstract: Photometry of stars, relative to one another in a single CCD field, has been done at the +/- 0.004 mag accuracy level. To achieve this, careful account of the method of constructing the flat-field calibration, of the effect of stellar profile variations across the field, and of the effect of nearby stars has had to be taken. Using this accuracy, a study of the intrinsic width of the lower red-giant branch in the M13 color-magnitude diagram has been made. The observed standard deviation of the scatter in V-R color away from the CMD giant branch locus is 0.0053 (+/- 0.0013) mag. As the weighted mean measuring uncertainty for the stars used to derived this scatter was 0.0066 (+/- 0.0020) mag, this implies that there is only a 15 percent chance that the intrinsic scatter is larger than 0.0026 mag.
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