Advanced Camera for Surveys Instrument Handbook for Cycle 14
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| Advanced Camera for Surveys Instrument Handbook for Cycle 14 | |||||
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12.1 Summary of AccuraciesChapter 12:
Calibration Accuracies
In this Chapter we describe the accuracies that can be expected from ACS observations.
12.1 Summary of Accuracies
In the tables below we list the accuracy that we expect to achieve from the planned calibration program. These estimates reflect the current understanding of the instrument and may need to be updated once additional calibration data have been obtained and thoroughly analyzed. Updates will be available on the ACS web pages (under "
Calibration Plan"). Although data will be analyzed according to our list of calibration priorities, all calibration data are immediately public and accessible through the HST archive so that users in need of extremely accurate or urgent results will be able to carry out their own calibration. The values quoted here are the results of pre-launch measures, of observations taken during SMOV, and of observations taken as part of the Cycles 11 and 12 calibration program.The extensiveness of our calibrations will also depend, in part, on the science programs selected by the proposers and the TAC. Clearly, we will spend little or no time calibrating filters or capabilities that are not requested by observers. We have selected a subset of the filters as those that we expect to receive heavy use; the accuracy numbers quoted here for photometric measurements are for WFC/F435W, WFC/F475W, WFC/F555W, WFC/F606W, WFC/F625W, WFC/F775W, WFC/F814W, WFC/F850LP, HRC/F330W, HRC/F435W, HRC/F475W, HRC/F555W, HRC/F606W, HRC/F625W, HRC/F775W, HRC/F814W and HRC/F850LP. The remaining filters may be subject to moderately higher levels of uncertainty.
The accuracies tabulated assume that the Poisson noise in the data is negligible. Clearly, low-S/N data will have accuracies dominated by this unavoidable noise source.
Table 12.1: WFC Accuracies
The values listed here are meant to reflect typical applications, in special circumstances it is possible to do much better (or worse as the case may be). For example, a program designed to perform differential time-series photometry has demonstrated photometric stability of 0.06% for 519 WFC exposures spanning 7 days using GAIN=2, pointing maintained to the same pixel throughout, and for strongly saturated (!) stars providing a low Poisson limit.
Table 12.2: HRC Accuracies
Table 12.3: SBC Accuracies
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