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K. Mighell (KPNO/NOAO)
I present the results of an investigation of the performance of CCD stellar photometry with a 1.5-\mum diffraction-limited 8-m Next Generation Space Telescope. These simulations used artificial Point Spread Functions for three different 8-m NGST design concepts which were kindly provided by John Krist. Assuming that the 8-m NGST primary mirror has 1/13 wave RMS errors at 1.5 \mum, I demonstrate that 90% of the light from a star falls within an aperture radius of 0.1 arcsec --- the size of one WF pixel of the {\sl{Hubble Space Telescope}} WFPC2 instrument. The three NGST design concepts have nearly identical V\!-band encircled-energy functions; the degradation caused by the differences between the different design concepts is quite negligible when state-of-the-art digital-PSF photometric reduction software is used to analyze uncrowded stellar fields. All the V\!-band PSFs used in these simulations were sampled at 0.0064 arcsec pixel-1 which is the critical V\!-band sampling rate of a perfect 0.5-\mum diffraction-limited 8-m NGST. Better photometric performance for all three NGST design concepts could be obtained by using larger CCD pixels: a pixel size of ~0.013 (\approx 2\times0.0064) arcsec pixel-1 should provide an optimal pixel sampling when the 8-m primary mirror is diffraction-limited at 1.5 \mum.
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The author(s) of this abstract have provided an email address for comments about the abstract: mighell@noao.edu