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R.M. Rich (UCLA), J.D. Neill (Columbia U.)
While the Next Generation Space Telescope has as its prime mission the direct imaging of the high redshift Universe, it will also be capable of greatly advancing the study of stellar populations in nearby galaxies. To explore what capabilities NGST might have in this area, we simulate a 10 hour integration in the V,I passbands using a detector with WFPC2-like noise characteristics, on a field in the halo of M31. The model input color-magnitude diagram (CMD) and luminosity function (LF) were chosen to be identical to that of 47 Tuc, in an M31 halo field with a presumed surface brightness of V=24 mag per sq. arcsec. The simulated CMD reaches 2 mag below the turnoff and the luminosity function is complete to that level. The input point spread functions assumed an NGST diffraction limited only at 1 micron. If NGST performed this well, it would be conceivable to age date all the population II halos and globular clusters in the Local Group, and reach the horizontal branch in Virgo. We strongly advocate that NGST is capable of reaching at least 6000A in an imaging mode, and that every effort be made to control diffracted and scattered light.
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