A detailed description of this new and improved CALACS will be available in a future publication of ACS Data Handbook. In the meantime, if you have questions not answered in this documentation, please contact STScI Help Desk (help[at]stsci.edu).
CALACS is now part of HSTCAL package, which can be downloaded from
http://www.stsci.edu/institute/software_hardware/stsdas/download-stsdas
CALACS supports several command line options:
By default, CALACS will attempt to perform PCTECORR using all available CPUs on your machine. You can set the maximum number of CPUs available for CALACS by setting the OMP_NUM_THREADS environmental variable.
In tcsh:
setenv OMP_NUM_THREADS 2
In bash:
export OMP_NUM_THREADS=2
The recommended method for running CALACS in batch mode is to use Python and the acstools package in STSDAS distribution.
For example:
from acstools import calacs
import glob
for fits in glob.iglob('j*_raw.fits'):
calacs.calacs(fits)
BIASCORR is now performed before BLEVCORR. This should not significantly affect science results. This change was necessary to accomodate BIASFILE subtraction in DN with the rest of the calculations done in ELECTRONS.
The image is multiplied by gain right after BIASCORR, converting it to ELECTRONS. This step is no longer embedded within FLATCORR.
BLEVCORR is now performed after BIASCORR. Calculations are done in ELECTRONS.
For post-SM4 full-frame WFC exposures, it also includes:
- de-striping to remove stripes introduced by new hardware installed during SM-4 (J. Anderson; ACS ISR 2011-05); and
- if JWROTYPE=DS_int and CCDGAIN=2, also correct for bias shift (ACS ISR 2012-02) and cross-talk (N. Grogin; ACS ISR 2010-02).
For all full-frame WFC exposures, pixel-based CTE correction (ACS ISR 2010-03 and 2012-03) is applied at the end of the ACSCCD series; i.e., after BLEVCORR.
Because the CTE correction is applied before DARKCORR and FLSHCORR, it is necessary to use a CTE-corrected dark (DRKCFILE) and post-flash (FLSCFILE) if the PCTECORR step is enabled.
Parameters characterizing the CTE correction are stored in a reference table, PCTETAB.
Running CALACS with pixel-based CTE correction requires the following header keywords:
You may adjust some CTE correction algorithm parameters by changing the following keywords in RAW image header. The default values are picked for optimum results in a typical WFC full-frame exposure. Changing these values is not recommended unless you know what you are doing.
It uses DARKFILE if PCTECORR=OMIT, otherwise it uses DRKCFILE (CTE-corrected dark reference file).
Dark image is now scaled by EXPTIME and FLASHDUR. For post-SM4 non-BIAS WFC images, extra 3 seconds are also added to account for idle time before readout. Any image with non-zero EXPTIME is considered not a BIAS.
Post-flash correction is now performed after DARKCORR in the ACS2D step. When FLSHCORR=PERFORM, it uses FLSHFILE if PCTECORR=OMIT, otherwise it uses FLSCFILE (CTE-corrected post-flash reference file).
Conversion from DN to ELECTRONS no longer depends on FLATCORR=PERFORM. Unit conversion is done for all exposures after BIASCORR.
The PHOTCORR step is now performed using tables of precomputed values instead of calls to SYNPHOT. The correct table for a given image must be specified in the IMPHTTAB header keyword in order for CALACS to perform the PHOTCORR step. By default, it should be in the jref directory and have the suffix _imp.fits. Each DETECTOR uses a different table.
If you do not wish to use this feature, set PHOTCORR to OMIT.
Using RAW as input:
- flt.fits: Same as existing FLT.
- flc.fits: Similar to FLT, except with pixel-based CTE correction applied.
Using ASN as input with ACSREJ:
- crj.fits: Same as existing CRJ.
- crc.fits: Similar to CRJ, except with pixel-based CTE correction applied.