The response of pixels in CCDs and CMOS arrays is not uniform; physical aspects of pixel structure can create non-uniform electric fields within a pixel and the diffusion of carriers tends to blur pixel boundaries. It has previously been shown that the sub-pixel response can vary by up to 50% across a pixel, with more light being detected near the center and less around the edges. This intra-pixel response function (IPRF) can have significant effects on the aperture photometry of under-sampled PSFs, like those found in the Kepler and TESS exoplanet hunting missions. Knowledge of the IPRF can be used to correct for systematic variations in photometric measurements introduced by the sub-pixel variations in response. Additionally, in systems for which the optical PSF is not well defined, knowledge of the IPRF can allow for extraction of the optical PSF.
Presented here are the results of the direct measurement of the IPRF of a thinned, back-illuminated CCD of the same model used on the NASA Kepler mission. The experimental setup used to measure the IPRF is discussed in detail. Measurements of the IPRF were made at various wavelengths, then combined to create an "effective IPRF" for the broad spectral bandpass filter used for collecting the scientific data of interest. This effective IPRF was then utilized in a model to study the effects of the IPRF on time series aperture photometry. The effects of spacecraft jitter and drift on aperture photometry were also investigated. Such results are relevant for exoplanet searches using the photometric detection technique as implemented in the Kepler and TESS missions.
Library of Congress Subject Headings
Astronomical photometry; Metal oxide semiconductors, Complementary; Imaging systems--Image quality
Imaging Science (MS)
Department, Program, or Center
Chester F. Carlson Center for Imaging Science (COS)
Irwin, Alexis M., "Sub-pixel Sensitivity Variations and their Effects on Precision Aperture Photometry" (2020). Thesis. Rochester Institute of Technology. Accessed from
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