This chapter contains plots of throughputs for each imaging mode in Section 10.3.1
. Section 9.2
explains how to use these throughputs to calculate expected count rates from your source.
The first figure for each imaging mode gives the integrated system throughput, which is the combination of the efficiencies of the detector and of the optical elements in the light path. The throughputs in this handbook are based in part on ground test data, although at the time of writing the handbook, the overall detector efficiency curve and most filter throughputs have been adjusted based on in-flight data. The total system unitless quantum efficiency, i.e., throughput, at any wavelength is defined as the probability that a monochromatic photon incident on the primary mirror produces a detected photo-electron. For the CCD, "
is the number of electrons detected. For the MAMA, "
is the number of valid photo-electron events processed by the detector electronics after passing through the various pulse-shape and anti-coincidence filters. In both cases, the detected counts obey Poisson statistics. The throughput includes all reflections and transmissions in the optical train (e.g., due to the HST
To recalculate the throughput with the most recent CCD QE tables in pysynphot
, you can create total-system-throughput tables (instrument plus OTA) using the pysynphot.ObsBandpass
A bandpass object is created by providing any valid obsmode
command string as an argument to pysynphot.ObsBandpass
. For example, to evaluate the throughput of the F475W filter and the WFC detector, chip 1, you would use the command:
For each imaging mode, plots are provided to estimate the signal-to-noise ratio (S/N) for a representative source, see Section 10.3.1
. The first figure shows S/N for point sources (GAIN=1
). The second figure shows S/N for uniform extended sources of area 1 arcsecond2
The point- and extended-source S/N figures are shown for average and low sky levels. For point sources, an aperture size of 5 x
is used for the WFC, 9 x
for HRC, and 15 x
for the SBC S/N evaluation. For extended sources, a 1 arcsecond2
aperture is used. For the CCD the read noise is computed assuming a number of readouts NREAD
/1000 seconds), where t
is the exposure time, with a minimum NREAD=2
. That is, each exposure has a minimum CR-SPLIT=2
. Different line styles in the figures are used to indicate which source of noise dominates.