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.