|ACS Data Handbook v. 9.0|
The calacs package consists of five tasks listed in Table 3.2. These tasks, available in the HSTCAL package, are automatically called by calacs, but each may be run separately, via acstools in AstroConda.Table 3.2: Tasks in the calacs Pipeline
CTE corrections for WFC images1 CTE loss correction is available for a WFC 2K subarray of the old format or any WFC subarray of the new format. The subarray formats were switched from old to new during Cycle 24, in May 2016. However, due to uncorrected striping in all WFC subarrays, PCTECORR is set to OMIT by default in the pipeline for all subarrays. To perform CTE loss correction for an eligible WFC subarray, please set PCTECORR to PERFORM in the image header and use the 'acs_destripe_plus' task in acstools. See also Example 5 Section 3.5.2.
The flow of data through the ACS calibration pipeline and the decisions made while working with associated data are shown in Figures 3.1, 3.2, and 3.3. They're also outlined below with the calacs tasks and functions in parenthesis.
1. Flag known bad pixels and saturated pixels in the data quality (DQ) array. (acsccd/doDQI or acs2d/doDQI)
2. Subtract the bias image (CCD only). (acsccd/doBias)
3. Multiply by gain to convert DN to electrons. (acsccd/toElectrons or acs2d/toElectrons)
5. Flag sink pixels in the DQ array of WFC images. (acsccd/doSink)
6. Calculate a noise model for each pixel and record it in the error (ERR) array. (acsccd/doNoise or acs2d/doNoise)
9. Perform global linearity corrections (MAMA only). (acs2d/doNonLin)
12. Divide the image by the flat field. (acs2d/doFlat)
13. Apply shutter shading correction (CCD only). (acs2d/doShad)
14. Calibrated flt.fits/flc.fits images from "CR-SPLIT" exposures, repeated sub-exposures, "POS TARG" exposures, or dither "PATTERN" exposures may be combined using AstroDrizzle. Please refer to the DrizzlePac website for information regarding drizzling the images.As indicated in Figure 3.1, calibration tasks that are detector-specific (like acsccd for WFC data only) have been separated from tasks that can process both detectors (such as acs2d).The initial processing performed on CCD data alone is shown in Figure 3.2. Reference files appropriate for each processing step and the calibration switches controlling them are also given beside the name of the task they control. The output (overscan-trimmed image) from acsccd is then sent through acscte (if appropriate) and acs2d as shown in Figure 3.3.Processing of raw MAMA data begins with acs2d, which initializes the error and data quality arrays (a step that was performed earlier for CCD data) and applies linearity corrections.Figure 3.1: Flow Diagram for ACS Data, With calacs Task NamesCRCORR Combine observations to reject cosmic rays (CCD only).RPTCORR Add individual repeat observations (SBC MAMA only).DRIZCORR Drizzle processing.Figure 3.2: Flow Diagram for CCD Data Using acsccd and acscte in calacs* The overscan areas are trimmed only if the raw image had "BLEVCORR=PERFORM." In almost all cases, this is the default value. Only in rare instances will that keyword be set to "OMIT."Figure 3.3: Flow Diagram for MAMA and Overscan-Trimmed CCD Data Using acs2d in calacs