Space Telescope Science Institute   5.2.2 Throughputs and Limiting Magnitudes  5.2.4 Signal-To-Noise Ratios

5.2.3 Limiting Magnitudes


Table 5.5 contains Johnson-Cousins V magnitudes for unreddened O5 V, A0 V, and G2 V stars, generated using the Exposure Time Calculator. WFC and HRC values used the parameters CR-SPLIT=2, GAIN=2, and a 0.2 arcsecond circular aperture. For the SBC, a 0.5 arcsecond circular aperture was used. An average sky background was used in these examples. However, limiting magnitudes are sensitive to the background levels; for instance, the magnitude of an A0 V in the WFC using the F606W filter changes by ±0.4 magnitudes at the background extremes.

Figure 5.7: ACS CCD system throughputs + OTA versus those of STIS and WFPC2.

 

Table 5.5: V detection limits for ACS, HRC, and SBC direct imaging.
Camera
Filter
V limit (S/N = 5, exposure time = 1 hour)


O5 V (Kurucz model)
A0 V (Vega)
G2 V (Sun)
WFC
F606W
27.8
27.8
28.0
WFC
F814W
26.7
27.0
27.7
HRC
F330W
26.8
24.8
24.1
HRC
F606W
27.3
27.3
27.5
SBC
F125LP
27.8
23.2
13.5

 5.2.2 Throughputs and Limiting Magnitudes  5.2.4 Signal-To-Noise Ratios
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