Author : Joanna Schafer
Detector : HRC
Compare thermal vacuum response of HRC to tungsten lamps with previously computed models. Tests were run through five different filters.
Median counts were found for each frame using the ACS_STATS routine in IDL. As noted above, the particular median quoted is (Image - Trailing Serial). Then to get count rate, the average of the bias medians was subtracted from each median value; next the bias-corrected median value was divided by exposure time and multiplied by the gain for HRC build 1, 1.16 counts/e-.
For both the tung3 and tung4 lamps, the measured count rate was upwards of 1.6 times as large as that predicted in all filters. Notice how the experimental/model count rate ratio increases with wavelength starting with F475W; the rise shortward of that filter is attributed to scattered light. This particular problem should be corrected by flight time.
Otherwise, the different illumination patterns of the two tungsten lamps are compared via a ratio image below. Pay attention to the higher intensities on the right hand edge. Since the image is tung4/tung3 in F625W, the bright areas show where the tung4 lamp illuminates better, and vice versa.
Also of interest, the time for signal to noise to reach 100 flat in the F475W filter is just 1.2 s, well within CEI specs. The goal was to reach that S/N in 10 hours or less.
|Figure 2a : ID 5589||Figure 2b : ID 5591|
|Figure 2c : ID 5594||Figure 3 : Ratio of ID 5596 to ID 5589|