
438 17. Detectors, Signal-to-Noise, and Detection Limits
Therefore the slope in a log (SNR) versus magnitude plot is different by a factor
of two in the two regions.
17.4.
DETECTION LIMITS: STELLAR PHOTOMETRY
We now take Eq. (17.3.4) and give results for HST and ground-based
telescopes of different aperture, each with the same detector and filter character-
istics.
The parameters used for the calculations are given in Table 17.3, with
characteristics for the CCD taken from Table 17.1.
We choose
K:
= 0.8 for all telescopes and assume this fraction of the
transmitted light contributes to the detected signal. For the wide-field mode of
ACS,
th