The initial scheduling was completely automatic, based on the algorithm described below. Further hand editing was to put in DARK and scattered-light calibrations, and to allow more time for guide star acquisitions.
10-sigma limits (20 pix area) Filter Nexp hours counts/s AB mag F300W 100 48.93 0.0148 27.47 F450W 62 36.52 0.0232 28.12 F606W 77 34.94 0.0370 28.71 F814W 49 34.86 0.0299 28.02The limits are roughly 0.2 mag brighter than originally projected.
Pass 1 schedules long bright & dark windows Bright: minimum background > 7.5e-7 erg cm-2 s-1 A-1 arcsec-2 (= 22.4 ABMAG in F814W) Dark: maximum background < 4.7e-7 (22.95 ABMAG in F814W) Long: > 2100 sec Bright windows all go to F300W Dark windows are parceled equally to F450W, F606W, and F814W. Most of the observing time was scheduled in this pass. Pass 2 schedules gray periods which are either Darkish: maximum background < 6.9e-7 (22.5 ABMAG in F814W), with t>2100 sec Gray: mean F814W background <= 6.9e-7 (22.5 ABMAG in F814W) with t>500 sec In practice, only a small fraction of these windows have mean background more than 1.2 times the minimum, so these are essentially dark time, except that they are more prone to any uncertainties in the scattered light model. In scheduling these periods, there is some attempt to give F450W preference for long observing times. At the lowest background levels, the required integration time for sky noise to equal read noise is 1740, 390, and 780 sec for F450W, F606W, and F814W, respectively. So F606W gets all the observing windows shorter than 500 sec, F814W gets all the windows with 500 < t < 1800 sec, and the longer windows are split between F450W, F606W, and F814W, but with more weight given to choosing F450W. Pass 3 schedules the remaining periods with t>300 sec Periods with mean background in F814W > 1.4e-6 are given to F300W Periods with mean background in F814W < 6.0e-7 are given to F606W if 300 < t < 1000 sec F814W if 1000 < t < 1500 sec F450W if t > 1500 sec Periods with mean background b in F814W 6.0e-7 < b < 1.4e-6 are given to F300W if t < 1000 sec F814W if 1000 < t < 1500 sec F450W if t > 1500 sec In practice 87% of these windows have mean background more than 1.5 times the minimum, so these really are not adding much to our S/N in the red filters.Copyright © 1997 The Association of Universities for Research in Astronomy, Inc. All Rights Reserved.