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A. Sivaramakrishnan, R. B. Makidon, D. F. Figer, L. E. Bergeron, R. I. Jedrzejewski, H. B. Bushouse, H. S. Stockman, P. E. Hodge, N. M. Dencheva, B. J. Rauscher (STScI), J. J. Green, P. Dumont, D. C. Redding (JPL), M. Im (IPAC), J. D. Offenberg (SSAI), STScI Team, JPL Team, IPAC Team, SSAI Team
The James Webb Space Telescope (JWST) will be a segmented, deployable, infrared-optimized 6.5m space telescope. Its active primary segments will be aligned, co-phased, and then fine-tuned in order to deliver image quality sufficient for the telescope's intended scientific goals. Wavefront sensing used to drive this tuning will come from the analysis of focussed and defocussed images taken with its near-IR science camera, NIRCAM. There is a pressing need to verify that this will be possible with the near-IR detectors that are still under development for JWST. We create simulated NIRCAM images to test the maintenance phase of this plan. Our simulations incorporate real detector noise typical of near-IR detectors, Poisson noise, cosmic rays, and can be extended to model persistence, cross-talk, and other image anomalies as the Independent Detector Testing Laboratory obtains them from JWST detector candidates. Simulating InSb detectors can also be done within this framework in future. We generate Point-Spread Functions (PSF's) for a segmented aperture geometry with various wavefront aberrations, and convolve this with typical galaxy backgrounds and stellar foregrounds. We then simulate up-the-ramp (MULTIACCUM in HST parlance) exposures with cosmic ray hits. We pass these images through the HST NICMOS `CALNICA' calibration task to filter out cosmic ray hits. The final images can also be used for a variety of observational program exposure time estimates in addition to wavefront sensing algorithm testing, in order to find the ranges of exposure times, filter bandpass, defocus, and calibration star magnitude required to keep the JWST image within its specifications.
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.