Section 10. Advanced Camera For Surveys
Observations made with the Advanced Camera for Surveys (ACS) are processed by the task calacs, which makes use of the calibration files described in this chapter. More details about the files and their use in calacs may be found in ACS ISR 99-08, “CALACS Reference Files” (Hack, 1999) and the ACS Data Handbook (Lucas et al., 2022). The calibration files contribute to AstroDrizzle which is also used to perform distortion correction on all ACS images.
10.1 File Formats and Conventions
Continuing the style of STIS and NICMOS, all ACS reference files are FITS files with extensions. They have names of the form <uniquename>_xyz.fits where <uniquename> is a nine character unique name, the last character of which will be “j” for all ACS files. The leading eight characters are based on the date and time when the file was created. “xyz” represents the type of calibration file and will a three character string representing the reference file type which is given in the following sections. ACS has three detectors known as the Wide Field Channel (WFC), the High Resolution Channel (HRC), and the Solar Blind Channel (SBC), distinguished by the keyword DETECTOR, which may take the values WFC, HRC, and SBC. The WFC is composed of two CCDs, each having 2048 columns and 4144 rows of pixels (48 columns of which are physical prescan equally divided between the left and right sides of the CCDs; prescan columns are removed during calibration). The data from this and the corresponding calibration files contain two imsets in a single FITS file. The extension headers contain the keyword CCDCHIP, which take the value 2 for imset 1 and the value 1 for imset 2. The HRC has 1024 rows and 1062 columns of pixels (38 columns of which are physical prescan similar to the WFC design). SBC is read out as a 1024 x 1024 image. Both HRC and SBC data are stored in FITS files as single imsets. Two- dimensional bias images (BIASFILE) contain the overscan regions, while other reference files do not.
10.2 ACS Calibration Reference Files
The header for an ACS reference image will be in the format below. The list is derived from ACS ISR 99-05, “Design of the ACS Science Headers” (Jedrzejewski, 1999), with observation-specific keywords removed and the calibration keywords DESCRIP, PEDIGREE, and USEAFTER added. A calibration file header can easily be created by editing an observation header. The keyword FILETYPE is used quite differently in calibration files and is specified below for each type of calibration file. Each string must exactly match the values specified and will be checked before being accepted by CRDS.
Not all of the listed keywords are strictly required. For instance the EXPOSURE INFORMATION set is largely meaningless for a calibration file, which may be derived from multiple observations. However, the EXPTIME must be given for such things as dark rate images and should normally have the value 1 second. In general it is simplest to include the whole group because the science headers contain them. There is no problem caused by having extra keywords in the header; unneeded ones are simply ignored. The ENGINEERING PARAMETERS and CALIBRATED ENGINEERING PARAMETERS groups are only meaningful for the CCD images, namely those from the HRC and WFC.
The DESCRIP keyword contains a brief description of the data. More extensive information should be supplied in the reason for delivery when submitted to CRDS. It may be convenient to keep the same information as history lines in the file header. PEDIGREE can have the values DUMMY, GROUND, or INFLIGHT. If the value DUMMY is present, the pipeline will skip the related calibration step even if the switch is set to PERFORM. The USEAFTER keyword contains the date from which the file is to be applied, superseding any other files with the same selection parameter values and earlier USEAFTER dates.
ACS File Header
SIMPLE = T data conform to FITS standard L1
BITPIX = bits per data value I2
NAXIS = 0 number of data axes I2
EXTEND = T file may contain standard extensions L1
NEXTEND = number of standard extensions I2
GROUPS = F image is in group format L1
DATE = date this file was written (yyyy-mm-dd) C10
FILENAME = name of file C18
FILETYPE = calibration file type C67
TELESCOP = HST telescope used to acquire data C03
INSTRUME = identifier for instrument used to acquire data C06
EQUINOX = 2000.0 equinox of celestial coord. System R4
/ CRDS KEYWORDS
PEDIGREE = data source is DUMMY, GROUND, or INFLIGHT C8
DESCRIP = a brief description of the data C67
USEAFTER = 25 Mar 1999 date following which this file applies C12
/ DATA DESCRIPTION KEYWORDS
ROOTNAME = rootname of the observation set C09
IMAGETYP = type of exposure identifier C18
PRIMESI = instrument designated as prime C06
/ EXPOSURE INFORMATION
DATE-OBS = UT date of start of observation (yyyy-mm-dd) C10
TIME-OBS = UT time of start of observation (hh-mm-ss) C08
EXPSTART = exposure start time (Modified Julian Date) R8
EXPEND = exposure end time (Modified Julian Date) R8
EXPTIME = exposure duration (seconds)--calculated R4
EXPFLAG = NORMAL exposure interruption indicator C13
/ SCIENCE INSTRUMENT CONFIGURATION
OBSTYPE = observation type - imaging or spectroscopic C14
OBSMODE = operating mode C08
SCLAMP = lamp status, NONE, or name of lamp which is on C09
NRPTEXP = number of repeat exposures in set: default 1 I2
SUBARRAY = data from a subarray (T) or full frame (F) L1
DETECTOR = detector in use: WFC, HRC, or SBC C03
FILTER1 = element selected from filter wheel 1 C18
FILTER2 = element selected from filter wheel 2 C18
LRFWAVE = proposed linear ramp filter wavelength R4
APERTURE = aperture name C16
CRSPLIT = number of cosmic ray split exposures I2
/ ENGINEERING PARAMETERS
CCDAMP = CCD amplifier readout configuration C04
CCDGAIN = commanded gain of CCD I2
CCDOFSTA = commanded CCD bias offset for amplifier A I4
CCDOFSTB = commanded CCD bias offset for amplifier B I4
CCDOFSTC = commanded CCD bias offset for amplifier C I4
CCDOFSTD = commanded CCD bias offset for amplifier D I4
/ CALIBRATED ENGINEERING PARAMETERS
ATODGNA = calibrated gain for CCD amplifier A R4
ATODGNB = calibrated gain for CCD amplifier B R4
ATODGNC = calibrated gain for CCD amplifier C R4
ATODGND = calibrated gain for CCD amplifier D R4
READNSEA = calibrated read noise for amplifier A R4
READNSEB = calibrated read noise for amplifier B R4
READNSEC = calibrated read noise for amplifier C R4
READNSED = calibrated read noise for amplifier D R4
END
XTENSION = extension type C08
BITPIX = bits per data value I2
NAXIS = 2 number of data axes I2
NAXIS1 = length of first data axis I4
NAXIS2 = length of second data axis I4
PCOUNT = 0 number of group parameters I2
GCOUNT = 1 number of groups I2
TFIELDS = number of fields in each table row I2
INHERIT = T inherit the primary header L1
EXTNAME = extension name C06
EXTVER = extension version number I2
ROOTNAME = rootname of the observation set C09
EXPNAME = 9 character exposure identifier C09
DATAMIN = the minimum value of the data R8
DATAMAX = the maximum value of the data R8
BUNIT = brightness units C18
BSCALE = 1.0 scale factor for array value to physical value R8
BZERO = 32768. physical value for an array value of zero R8
/ WFC CCD CHIP IDENTIFICATION
CCDCHIP = CCD chip (1 or 2) I2
/ World Coordinate System and Related Parameters
LTV1 = 0 offset in X to subsection start R4
LTV2 = 0 offset in Y to subsection start R4
LTM1_1 = 1 reciprocal of sampling rate in X R4
LTM2_2 = 1 reciprocal of sampling rate in Y R4
/ READOUT DEFINITION PARAMETERS
CENTERA1 = subarray axis1 center pt in unbinned detector pixels I4
CENTERA2 = subarray axis2 center pt in unbinned detector pixels I4
SIZAXIS1 = subarray axis1 size in unbinned detector pixels I4
SIZAXIS2 = subarray axis2 size in unbinned detector pixels I4
BINAXIS1 = 1 axis1 data bin size in unbinned detector pixels I2
BINAXIS2 = 1 axis2 data bin size in unbinned detector pixels I2
/SBC-SPECIFIC PARAMETERS
MOFFSET1 = axis 1 MAMA offset I2
MOFFSET2 = axis 2 MAMA offset I2
END
XTENSION = extension type C08
BITPIX = bits per data value I2
NAXIS = 2 number of data axes I2
NAXIS1 = length of first data axis I4
NAXIS2 = length of second data axis I4
PCOUNT = 0 number of group parameters I2
GCOUNT = 1 number of groups I2
TFIELDS = number of fields in each table row I2
INHERIT = T inherit the primary header L1
EXTNAME = extension name C06
EXTVER = extension version number I2
ROOTNAME = rootname of the observation set C09
EXPNAME = 9 character exposure identifier C09
DATAMIN = the minimum value of the data R8
DATAMAX = the maximum value of the data R8
BUNIT = brightness units C18
NPIX1 = length of constant array axis 1 I4
NPIX2 = length of constant array axis 2 I4
PIXVALUE = values of pixels in constant array R4
/ World Coordinate System and Related Parameters
LTV1 = 0 offset in X to subsection start R4
LTV2 = 0 offset in Y to subsection start R4
LTM1_1 = 1 reciprocal of sampling rate in X R4
LTM2_2 = 1 reciprocal of sampling rate in Y R4
END
XTENSION = extension type C08
BITPIX = bits per data value I2
NAXIS = 2 number of data axes I2
NAXIS1 = length of first data axis I4
NAXIS2 = length of second data axis I4
PCOUNT = 0 number of group parameters I2
GCOUNT = 1 number of groups I2
TFIELDS = number of fields in each table row I2
INHERIT = T inherit the primary header L1
EXTNAME = extension name C06
EXTVER = extension version number I2
ROOTNAME = rootname of the observation set C09
EXPNAME = 9 character exposure identifier C09
DATAMIN = the minimum value of the data R8
DATAMAX = the maximum value of the data R8
BUNIT = brightness units C18
NPIX1 = length of constant array axis 1 I4
NPIX2 = length of constant array axis 2 I4
PIXVALUE = values of pixels in constant array I4
/ World Coordinate System and Related Parameters
LTV1 = 0 offset in X to subsection start R4
LTV2 = 0 offset in Y to subsection start R4
LTM1_1 = 1 reciprocal of sampling rate in X R4
LTM2_2 = 1 reciprocal of sampling rate in Y R4
END
10.2.1 Bias File (BIA): <unique name>_bia.fits
Description: The bias reference file (BIASFILE) is a combination of several bias exposures taken between CCD anneals and is responsible for removing the fixed bias structure and readout dark current from CCD science images.
Format: Prior to Servicing Mission 4 (SM4) in May 2009, and after the start of Cycle 24 (October 1, 2016), BIASFILEs have the dimensions of the full-frame readout including the physical bias prescan columns: (1062 x 1044) for HRC and (4144 x 2068) for WFC. During the period between SM4 and Cycle 24, additional subarray BIASFILEs were required. As of September 2021, subarray BIASFILEs are available for pre-SM4 data using supported subarray configurations.
The bias calibration step occurs prior to trimming off the overscan regions. Calacs also assumes that CCD data is not being read out in binned mode, and any image which does not have the same size as the full size image is a subarray readout. BIASFILEs are in units of data numbers (DN). Although the exposure time is not used by calacs, the EXPTIME keyword should be set to 0.0.
Selection Criteria: Selection is dependent on the DETECTOR, CCDAMP, CCDGAIN, APERTURE, NAXIS1, NAXIS2, RAW_LTV1 and RAW_LTV2 keywords.
Restrictions: Only for use with CCD detector data (DETECTOR != “SBC”).
Required Additional Keywords:
FILETYPE = “BIAS”
10.2.2 Dark File (DRK): <unique name>_drk.fits
Description: The dark reference file (DARKFILE) is a combination of several dark exposures taken over the span of days or weeks, and is responsible for removing dark current (i.e., excess thermal charge from the detector) from science images. As of January 15, 2015, WFC dark frames are post-flashed to mitigate the effects of Charge-Transfer-Efficiency (CTE) loss. This change required 1000.5 second “long” darks and 0.5 second “short” darks to be executed and subsequently used for WFC DARKFILE generation.
Format: DARKFILEs get applied after the overscan regions are trimmed from the input science image and therefore must have its overscan regions trimmed off as well. Dimensions of DARKFILEs are (1024 x 1024) for HRC and (4096 x 2048) for WFC. As with the BIASFILE, it is assumed that CCD images will not be binned, so any input image that is smaller than the full detector size is assumed to be a subarray image. DARKFILEs are in units of electrons/sec.
For CCD data, the dark image is multiplied by the DARKTIME value. This requires the dark image to already be scaled to an exposure time of 1 second and a gain of 1 (i.e., it is in units of electrons). The DARKTIME is just the exposure time and does not include the idle time since the last flushing of the chip or the readout time. For MAMA data, the dark image is just multiplied by the exposure time before subtracting, again, implying that the reference file be scaled to an exposure time of 1 second. This exposure time should be reflected in the EXPTIME keyword of the SCI array of the reference image.
Selection Criteria: Selection is dependent on the DETECTOR, CCDAMP and CCDGAIN keywords for the HRC and WFC, and only the DETECTOR keyword for the SBC. SBC science headers will not have entries for CCDAMP or CCDGAIN, so SBC DARKFILE headers will have values of “N/A” and –999 for these keywords, respectively.
Restrictions: None.
Required Additional Keywords:
FILETYPE = “DARK”
10.2.3 CTE Dark File (DKC): <unique name>_dkc.fits
Description: The CTE dark reference file (DRKCFILE) is simply the normal dark reference file (DARKFILE) that has been corrected for Charge-Transfer-Efficiency (CTE) by the pixel-based CTE correction.
Format: See the DARKFILE format in Section 10.2.2.
Selection Criteria: Selection is dependent on the DETECTOR, CCDAMP and CCDGAIN keywords.
Restrictions: Only for use with WFC data.
Required Additional Keywords:
FILETYPE = “CTE DARK”
10.2.4 Flat-Field Image Reference Files
ACS can utilize up to four flat-field reference files: the pixel-to-pixel flat field image (PFLTFILE), the low-order flat field image (LFLTFILE), the delta flat field image (DFLTFILE), and the coronagraphic spot flat image (CFLTFILE). If the LFLTFILE, DFLTFILE, or CFLTFILE reference images are not specified in the SCI image header, only the PFLTFILE is used for the flat-field correction.
These flat field images should all be scaled to an exposure time of 1 second, and the EXPTIME keyword should be updated to reflect this. All the flat-field files which are to be applied to the science data will be multiplied together to form a single flat field, then divided into the science data. In order to avoid any floating-point errors in this operation, none of the flat-field images should contain any pixels with a value of zero.
Subarray science images will use the same reference file as a full-size image; however, calacs will extract the appropriate region from the reference file and apply it to the subarray input image.
Note: Currently, only the PFLTFILE and CFLTFILE flat-field images are used for ACS data.
11.2.4.1 Pixel-to-Pixel Flat Field Image (PFL): <uniquename>_pfl.fits
Description: The pixel-to-pixel flat field image (PFLTFILE) represents the flat-field response for every pixel on the detector. In ACS, the PFLTFILE contains the low and high-order variations, while other instruments keep these effects in separate reference files.
Format: The PFLTFILE has the same size as an overscan-trimmed image: (4096 x 2048) for the WFC and (1024 x 1024) for the HRC and SBC.
Selection Criteria: Selection is dependent on the DETECTOR, CCDAMP, FILTER1, FILTER2 and OBSTYPE keywords. The OBSTYPE keyword can take on values of IMAGING, INTERNAL or CORONAGRAPHIC. For the SBC, selection does not use the CCDAMP or FILTER2 keywords and these keywords are instead given the value “N/A.”
Restrictions: The observation cannot be internal (OBSTYPE != “INTERNAL”).
Required Additional Keywords:
FILETYPE = “PIXEL-TO-PIXEL FLAT”
11.2.4.2 Coronagraphic Spot Flat Image (CFL): <uniquename>_cfl.fits
Description: The coronagraphic spot flat image (CFLTFILE) contains only the occulting spot patterns of the HRC coronagraph. The CFLTFILE is for use with HRC data only.
Format: The CFLTFILE has the same size as an overscan-trimmed HRC image, (1024 x 1024).
Selection Criteria: Selection is dependent on the DETECTOR, FILTER1, FILTER2 and OBSTYPE keywords. The OBSTYPE keyword must have a value of CORONAGRAPHIC.
Restrictions: For use with HRC coronagraphic observations only.
Required Additional Keywords:
FILETYPE = "SPOT FLAT"
10.2.5 Shutter-Shading Correction Image File (SHD): <unique name>_shd.fits
Note: As of May 2022, no need for SHADFILEs has been identified.
Description: The shutter-shading correction image reference file (SHADFILE) is designed to correct the image for the differential exposure time across the detector that results from the shutter travel time as it opens to start the exposure. SHADFILEs can be applied either during cosmic-ray rejection, should that be done for the observation, or during the basic processing in acs2d for single or REPEAT-OBS exposures.
The SHADFILE will be divided by the exposure time, have 1 added to it, then divided into the input science exposure during processing. The image header for this reference file should be the same as a science image taken with the same detector, with the keywords populated to reflect how the shutter-shading data was obtained. Future versions of these files may be delivered as mathematical models that can be applied to the data, rather than images, but the baseline version of calacs was designed to work with images.
Format: The SHADFILE has the size (512 x 256) for the HRC and WFC.
Selection Criteria: Selection is dependent on the DETECTOR keyword only.
Restrictions: Only for use with CCD detector data (DETECTOR != “SBC”).
Required Additional Keywords:
FILETYPE = "SHUTTER SHADING"
10.2.6 Post Flash Image File (FLS): <unique name>_fls.fits
Description: The post flash image reference file (FLSHFILE) is used to mitigate the effects of CTE loss. The FLSHFILE contains a short LED exposure which adds some background counts to the image. The FLSHFILE is of the same nature as a dark image and is normalized to a 1 second exposure. The science header has a keyword FLASHDUR, being the duration of the applied flash, which is muliplied by the FLSHFILE to create a scaled value of the flash image to be subtracted from the science image by calacs.
Format: The FLSHFILE has the same dimensions as a full size science image: (1024 x 1024) for the HRC and (4096 x 2048) for the WFC.
Selection Criteria: Selection is dependent on the DETECTOR, CCDAMP, CCDGAIN, FLASHCUR and SHUTRPOS keywords.
Restrictions: Only for use with CCD detector data (DETECTOR != “SBC”).
Required Additional Keywords:
FILETYPE = "POSTFLASH"
10.2.7 Geometric Delta Image File (DXY): <unique name>_dxy.fits
Note: DGEOFILE reference files are no longer used for ACS data calibration, and have been replaced by the NPOLFILE, D2IMFILE, and IDCTAB.
Description: The geometric delta image reference file (DGEOFILE) contains refinements to the geometric distortion correction beyond that defined by the high-order polynomial coefficients described in the IDC tables. There are corrections in the X and Y directions.
Use of these images is only for the most stringent astrometric applications and provides corrections of order 0.1 pixels. In most cases this calibration step can be omitted with no visible impact on the images or degradation of the analysis. Images have only been derived for a few filters and when a DGEOFILE is not available, this will not be considered an error. Calacs processing will continue omitting this step.
Format: For the WFC there are four images in the DGEOFILE, two for each chip, while DGEOFILEs for the HRC and SBC will have two image sets. The images will have the dimensions of a trimmed (no overscan) science image: (1024 x 1024) for the HRC and SBC, (4096 x 2048) for the WFC.
Selection Criteria: Selection is dependent on the DETECTOR, FILTER1, and FILTER2 keywords.
Restrictions: Only for use with pre-SM4 observations.
Required Additional Keywords:
FILETYPE = "DELTA XY"
10.2.8 Non-Polynomial Offset File (NPL): <unique name>_npl.fits
Description: The non-polynomial offset file (NPOLFILE) is a filter dependent, two-dimensional look-up table for each calibrated ACS pass-band. This table is used to correct fine-scale distortion of the non-polynomial irregularities. The NPOLFILE file is used for the pixel-by-pixel correction after the best-fit polynomial solution (IDCTAB) by bi-linear interpolation in the HST software DrizzlePac.
Format: For the WFC, each filter dependent NPOLFILE has four fits extensions: two extensions for each CCD chip, one in the X direction and one in the Y direction, each with sizes (64 x 32). For the HRC and SBC, NPOLFILEs have two fits extensions, one in the X direction and one in the Y direction, each with sizes (65 x 65).
Selection Criteria: Selection is dependent on the DETECTOR, FILTER1 and FILTER2 keywords.
Restrictions: Only for use with observations where DRIZCORR is set to PERFORM (DRIZCORR != “OMIT”).
Required Additional Keywords:
FILETYPE = "DXY GRID"
10.2.9 Column Correction File (D2I): <unique name>_d2i.fits
Description: The column correction reference file (D2IMFILE) is a two-dimensional look-up table for each of the WFC CCD chips to correct the lithographic-mask patterns. This table is used for pixel-by-pixel correction prior to the polynomial coefficients distortion by bi-linear interpolation in the HST software DrizzlePac.
Format: This D2IMFILE has four fits extensions: two extensions for each CCD chip, one in the X direction and one in the Y direction, each with sizes (64 x 32).
Selection Criteria: Selection is dependent on the DETECTOR keyword only.
Restrictions: Only for use with WFC observations where DRIZCORR is set to PERFORM (DRIZCORR != “OMIT”).
Required Additional Keywords:
FILETYPE = "WFC D2I FILE"
Note: As of May 2022, there is only one version of the D2IMFILE and it applies to WFC data only.
10.2.10 Sink Pixel Image File (SNK): <unique name>_snk.fits
Description: The sink pixel image reference file (SNKCFILE) is designed to identify and flag pixels containing an extreme number of charge traps, sink pixels, as well as adjacent affected pixels in WFC images. All WFC images obtained after January 2015 will have SINKCORR performed.
In the SNKCFILE, the location of each sink pixel is assigned a negative number corresponding to the number of electrons it traps. The adjacent pixel in the direction of the amplifier has the value -1 if it is anomalously high. Adjacent pixels in the opposite direction have values between 999.0 and 1. The remaining pixels are zero. The EXPTIME header keyword should be set to 0.0 even though it is not used by calacs.
Subarray science images will use the same reference file as a full-size image, however, calacs will extract the appropriate region from the reference file and apply it to the subarray input image.
Format: SNKCFILEs are applied before overscan trimming during the SINKCORR correction step in acsccd, so the dimensions of each extension of the fits file are the same as a full-size science image: (4144 x 2068).
Selection Criteria: Selection is dependent on the DETECTOR keyword only.
Restrictions: Only for use with WFC observations taken after January 2015.
Required Additional Keywords:
FILETYPE = "SINK PIXELS"
10.2.11 Full-Well Saturation Level Map File (SAT): <unique name>_sat.fits
Description: The full-well saturation level map reference file (SATUFILE) provides the full-well saturation level for every pixel on the detector, in units of electrons. For reference on the creation of this file, see ACS ISR 2020-02 (Cohen et. al, 2020).
The SATUFILE is used by calacs in order to identify full-well saturated pixels in the science image, and then add the appropriate flag value (256) to the corresponding pixels in the DQ image.
Format: SATUFILEs are applied in the calacs code between bias-correction (BLEVCORR) and sink pixel flagging (SINKCORR), so the dimensions of each extension of the fits file are the same as a full-size science image: (1062 x 1044) for HRC and (4144 x 2068) for WFC.
Selection Criteria: Selection is dependent on the DETECTOR and CCDAMP keywords for the HRC, and only the DETECTOR keyword for the WFC.
Restrictions: Only for use with CCD detector data (DETECTOR != “SBC”).
Required Additional Keywords:
FILETYPE = "SATUFILE"
10.3 ACS Tables
Tables are treated slightly differently from images by CRDS. For the ACS each type of table is supplied independently for each detector. Then, for each detector, the associated table must have rows for all calibrated modes. When a new table is delivered, it must contain rows matching all previously delivered rows, even if some of them are unchanged, because the previous table will not be referenced for observations later than the USEAFTER date. The new table may contain rows that did not appear in previous tables.
Table headers are quite simple, only needing the keywords shown in the tables below. The PEDIGREE and DESCRIP keywords appear in the table rows, since each row may have a different pedigree. The following is an example of some of the required keywords in an ACS reference table header:
ACS Table Header
SIMPLE = T / Data conform to Fits standard
BITPIX = 16 / Bits per pixel
NAXIS = 0 / Number of data axes
EXTEND = T / There may be standard extensions
DATE = '2022-04-01T16:47:04' / Date FITS file was generated
ORIGIN = 'astropy-fits' / FITS file originator
FILENAME = '64614292j_imp.fits' / Name of file
FILETYPE = 'Image photometry table' / Calibration file type
INSTRUME = 'acs' / Instrument name
DETECTOR = 'SBC' / Detector name
USEAFTER = 'Mar 01 2002 00:00:00' / Date from which table is applicable
10.3.1 Analog-to-Digital Table (A2D): <unique name>_a2d.fits
Note: ATODTAB files have never been used for ACS data calibration.
Description: The analog-to-digital table reference file (ATODTAB) provides the actual number of counts for each detected count in the image and allows for possible irregularities that might occur in the conversion such as were seen on the original WFPC. The conversion takes into account the gain setting, the amplifiers used, and, typically, the exposure time of the observation.
Format: Table 10-1 defines the ATODTAB table columns.
Table 10-1. Analog-to-Digital Table (A2D), <unique name>_a2d.fits
Column Name |
Data Type |
Units |
Description |
|---|---|---|---|
CCDAMP |
CH*4 |
– |
CCDAMP keyword value |
CCDGAIN |
S |
Electrons/DN |
Commanded gain |
CCDCHIP |
S |
– |
CHIP to which this conversion applies |
REF_KEY |
CH*12 |
– |
Usually EXPTIME |
REF_KEY_VALUE |
R |
– |
Values of REF_Key for different A- to-D conversions |
NELEM |
I |
– |
Number of elements in ATOD array |
ATOD |
R[65536] |
– |
Array with actual values |
PEDIGREE |
CH*67 |
– |
GROUND/DUMMY/INFLIGHT |
DESCRIP |
CH*67 |
– |
Short note describing this row |
Selection Criteria: Selection is dependent on the DETECTOR keyword. Table rows are selected by CCDCHIP, CCDAMP and CCDGAIN.
Restrictions: Only for use with CCD detector data (DETECTOR != “SBC”).
Required Additional Keywords:
FILETYPE = "ANALOG-TO-DIGITAL"
10.3.2 Bad Pixel Table (BPX): <unique name>_bpx.fits
Description: The bad pixel table reference file (BPIXTAB) maintains a record of all known bad pixels for each ACS detector. These pixels change with time as some hot pixels are annealed and others appear. Permanently bad pixels due to chip defects may be flagged during Generic Conversion, and it is the job of the BPIXTAB to maintain the list of bad pixels applicable for a given time period.
Format: The positions of the bad pixels are stored as pixel lists using the columns are defined in Table 10-2.
Table 10-2. Bad Pixel Table (BPX), <unique name>_bpx.fits
Column Name |
Data Type |
Units |
Description |
|---|---|---|---|
CCDAMP |
DESCRIP |
CH*67 |
– |
CCDGAIN |
CH*4 |
CH*67 |
– |
CCDCHIP |
S |
– |
– |
PIX1 |
S |
Electrons/DN |
CCDAMP keyword value |
PIX2 |
S |
– |
Commanded gain |
LENGTH |
S |
Pixel |
CHIP to which this conversion applies |
VALUE |
S |
Pixel |
X position of bad pixel list |
AXIS |
S |
Pixel |
Y position of bad pixel list |
PEDIGREE |
S |
– |
Number of bad pixels in this list |
The type of bad pixels which can be flagged are listed below. Some values are only marked during other processing steps (such as cosmic-ray rejection), but the VALUE column in this table specifies how the pixel is marked in the DQ array at the start of calibration processing.
Flag Value |
Definition |
|---|---|
0 |
Good pixel |
1 |
Reed-Solomon decoding error |
2 |
Data replaced by fill value |
4 |
Bad detector pixel or vignetted pixel |
8 |
Masked by aperture feature |
16 |
Hot pixel (dark current > 0.14 e¯/s) |
32 |
Pixels determined to be unstable throughout the course of an anneal cycle |
64 |
Warm pixel (dark current: 0.02–0.08 e¯/s pre-SM4; 0.04 to 0.08 e¯/s post-SM4; 0.06–0.14 e¯/s Jan 15, 2015 to present) |
128 |
Bias structure (mostly bad columns) |
256 |
Saturation (full well saturation) |
512 |
Bad pixel in reference file |
1024 |
Sink pixel or pixel affected by sink pixel charge traps |
2048 |
A-to-D saturation |
4096 |
Cosmic ray rejected by AstroDrizzle (based on all flt.fits/flc.fits files) |
8192 |
Cosmic ray rejected by acsrej |
16384 |
Reserved (satellite trail masks, etc…) |
Selection Criteria: Selection is dependent on the DETECTOR keyword only. Table rows are selected by CCDCHIP, CCDAMP and CCDGAIN, except when DETECTOR = SBC there is no row selection. The science header for the SBC does not have entries for CCDCHIP, CCDAMP, or CCDGAIN. As for the image keywords, the not applicable table entries show “N/A” or –999 according to the data type.
Restrictions: None.
Required Additional Keywords:
FILETYPE = "BAD PIXELS"
10.3.3 CCD Characteristics Table (CCD): <unique name>_ccd.fits
Description: The CCD characteristics table reference file (CCDTAB) provides the conversion from the commanded values to the calibrated values for each amplifier, given that each amplifier has its own readout characteristics and only a single value for these characteristics can be commanded by the observer. These calibrated values are then used during calacs processing to ensure that a pixel read out by an amplifier has been properly calibrated for that amplifier’s readout characteristics. The characteristics affected are readout noise (READNSE), A-to-D gain (ATODGN), bias offset level (CCDOFST), and bias level (CCDBIAS).
Format: Table 10-3 defines the CCDTAB table columns.
The CCDTAB contains one row for each amplifier configuration used in the readout. This configuration is uniquely identified by the list of amps used (CCDAMP), the particular chip being read out (CCDCHIP), the commanded gain (CCDGAIN), and the bin sizes of the pixels read out (BINAXIS). Each amp can be used to read out a section of the chip or the entire chip depending on how many amps are used to read out the observation.
As a result, the values AMPX and AMPY specify the boundaries between amp readout sections when used in concert to read out a chip. For multi-amp read out of a chip, AMPX specifies the first column affected by the second amp used to read out that row, and is set to zero when only one amp is used to read out each row. Similarly, AMPY specifies the first row affected by the second set of amps used to read out the chip, and is set to zero if only one amp or set of amps is used to read out the chip. AMPY is always set to zero for WFC observations since each chip only has one set of amps to read them out. These values are also used throughout calacs to determine which pixels were read out by which amp and apply the corresponding read noise, gain, and bias level to them.
In March 2020, the CCDTAB was updated to include two additional columns, OVFHFLS and OVFHUFLS, to represent the post-flashed and unflashed commanding overheads, respectively. These values are applied as an additive correction to the DARKTIME keyword already present in a given observation’s header.
In April 2020, the CCDTAB was updated again to include a new column, ATODSAT, containing new A-to-D saturation values based on the findings of the study described in ACS ISR 2020-03. It was shown that post-SM4 observations didn’t follow the previously-defined 65,535 DN A-to-D saturation limit rule, so all pre-SM4 (before January 2009) CCD observations use the 65,535 DN value, while post-SM4 pixels with 62,000 DN or higher are flagged. In this way the calibration of the data is reference file driven and not hard-coded.
Table 10-3. CCD Characteristics Table (CCD), <unique name>_ccd.fits
Column Name |
Data Type |
Units |
Description |
|---|---|---|---|
CCDAMP |
CH*4 |
– |
CCDAMP keyword value |
CCDCHIP |
S |
– |
Chip to which this conversion applies |
CCDGAIN |
S |
– |
Commanded gain |
CCDBIASA |
R |
– |
Commanded bias level for amp A |
CCDBIASB |
R |
– |
Commanded bias level for amp B |
CCDBIASC |
R |
– |
Commanded bias level for amp C |
CCDBIASD |
R |
– |
Commanded bias level for amp D |
CCDOFSTA |
S |
– |
Actual bias for amp A of CCD |
CCDOFSTB |
S |
– |
Actual bias for amp B of CCD |
CCDOFSTC |
I |
– |
Actual bias for amp C of CCD |
CCDOFSTD |
I |
– |
Actual bias for amp D of CCD |
BINAXIS1 |
S |
– |
Commanded bin size for axis 1 |
BINAXIS2 |
S |
– |
Commanded bin size for axis 2 |
ATODGNA |
R |
– |
Actual gain for amp A used for readout |
ATODGNB |
R |
– |
Actual gain for amp B used for readout |
ATODGNC |
R |
– |
Actual gain for amp C used for readout |
ATODGND |
R |
– |
Actual gain for amp D used for readout |
READNSEA |
R |
Electrons |
Calibrated value of readout noise for amp A |
READNSEB |
R |
Electrons |
Calibrated value of readout noise for amp B |
READNSEC |
R |
Electrons |
Calibrated value of readout noise for amp C |
READNSED |
R |
Electrons |
Calibrated value of readout noise for amp D |
AMPX |
S |
– |
First column affected by second amp |
AMPY |
S |
– |
First row affected by second set of amps |
ATODSAT |
R |
DN |
A-to-D saturation level |
SATURATE |
R |
DN |
CCD saturation threshold |
PEDIGREE |
CH*67 |
– |
How this row was created (DUMMY, GROUND) |
DESCRIP |
CH*67 |
– |
Short note describing this row |
OVFHFLS |
R |
Electrons |
Commanding overheads (post-flashed) |
OVFHUFLS |
R |
Electrons |
Commanding overheads (unflashed) |
Selection Criteria: Selection is dependent on the DETECTOR keyword only. Table rows are selected by CCDCHIP, CCDAMP and CCDGAIN.
Restrictions: Only for use with CCD detector data (DETECTOR != “SBC”).
Required Additional Keywords:
FILETYPE = "CCD PARAMETERS"
10.3.4 Overscan Region Table (OSC): <unique name>_osc.fits
Description: The overscan region table reference file (OSCNTAB) describes the overscan regions for each chip along with the regions to be used for determining the actual bias level of the observation.The OSCNTAB has no counterpart in any previous calibration pipelines.
Format: Table 10-4 defines the OSCNTAB table columns.
Each row in the OSCNTAB corresponds to a specific configuration as given by the amplifiers used (CCDAMP), the chip (CCDCHIP), and the size of the image with overscan regions (NX, NY).
The TRIMX columns give the number of columns to trim off the beginning and end of each line, while the TRIMY columns give the number of rows to trim off the top and bottom of each column. These completely specify the physical overscan regions for each chip, and these columns and rows are trimmed off the image during processing. The result of trimming (TRIMX1 + TRIMX2) columns from the image (NX) should result in the desired calibrated image sizes, 4096 for a full WFC image and 1024 for a full HRC image. The same can be said for NY - (TRIMY1 + TRIMY2), which should be 2048 for a full WFC image and 1024 for a full HRC image.
The BIASSECTA columns give the range of columns to be used for determining the bias level in the leading overscan region, while the BIASSECTB columns give the range of columns to be used to determine the bias level in the trailing overscan region. Finally, the virtual overscan starts at pixel (VX1, VY1) and extends to pixel (VX2, VY2). All coordinates and column numbers are specified in terms of the untrimmed image.
Table 10-4. Overscan Region Table (OSC), <unique name>_osc.fits
Column Name |
Data Type |
Units |
Description |
|---|---|---|---|
CCDAMP |
CH*4 |
– |
CCDAMP keyword value |
CCDCHIP |
S |
– |
Chip to which this conversion applies |
BINX |
S |
– |
Commanded bin size for axis 1 |
BINY |
S |
– |
Commanded bin size for axis 2 |
NX |
S |
Pixel |
Number of columns in image with overscan regions |
NY |
S |
Pixel |
Number of rows in image with overscan regions |
TRIMX1 |
S |
Pixel |
Number of columns to trim off beginning of each line |
TRIMX2 |
S |
Pixel |
Number of columns to trim off end of each line |
TRIMY1 |
S |
Pixel |
Number of lines to trim off beginning of each column |
TRIMY2 |
S |
Pixel |
Number of line to trim off end of each column |
BIASSECTA1 |
S |
– |
Beginning column for leading bias section |
BIASSECTA2 |
S |
– |
Ending column for leading bias section |
BIASSECTB1 |
S |
– |
Beginning column for trailing bias section |
BIASSECTB2 |
S |
– |
Ending column for trailing bias section |
VX1 |
S |
Pixel |
X coordinate of virtual overscan origin |
VX2 |
S |
Pixel |
Y coordinate of virtual overscan origin |
VY1 |
S |
Pixel |
X coordinate of top corner of virtual overscan region |
VY2 |
S |
Pixel |
Y coordinate of top corner of virtual overscan region |
PEDIGREE |
CH*67 |
– |
Pedigree of this row was created (DUMMY, GROUND, or INFLIGHT) |
DESCRIP |
CH*67 |
– |
Source and quality of specified overscan regions |
Selection Criteria: Selection is dependent on the DETECTOR keyword only. Table rows are selected by CCDCHIP and CCDAMP.
Restrictions: Only for use with CCD detector data (DETECTOR != “SBC”).
Required Additional Keywords:
FILETYPE = "OVERSCAN"
10.3.5 Cosmic-Ray Rejection Parameter Table (CRR): <unique name>_crr.fits
Description: The cosmic-ray rejection parameter table reference file (CRREJTAB) contains all the basic parameters necessary for performing cosmic-ray rejection. The cosmic-ray rejection process requires a number of input parameters to control how the cosmic-rays are detected. The process starts by creating a first guess for the CR-combined image either by median combining or minimum value combining the input CR-SPLIT exposures, as specified by INITGUES. Determination of the sky and noise values is controlled by the SKYSUB and SCALENSE values, respectively. Actual detection of the cosmic rays requires the specification of a threshold above which a pixel value is considered a cosmic ray (CRSIGMAS, CRTHRESH) and the distance from the detected pixel which the cosmic ray can affect other pixels (CRRADIUS). Once a pixel is determined to be affected by a cosmic ray, the value in BADINPDQ specifies the DQ value to use to mark that pixel in the exposure’s DQ array, if CRMASK was set to yes.
Format: Table 10-5 defines the OSCNTAB table columns.
Table 10-5. Cosmic-Ray Rejection Parameter Table (CRR), <unique name>_crr.fits
Column Name |
Data Type |
Units |
Description |
|---|---|---|---|
CRSPLIT |
S |
– |
Number of exposures observation was split into |
MEANEXP |
R |
Sec |
Average exposure time for each image |
SCALENSE |
CH*8 |
– |
Multiplicative noise in percents |
INITGUES |
CH*8 |
– |
Scheme of competing initial-guess image |
SKYSUB |
CH*4 |
– |
Sky levels subtraction scheme |
CRSIGMAS |
CH*20 |
– |
Rejection thresholds |
CRRADIUS |
R |
Pixel |
Radius (in pixels) to propagate the cosmic ray |
CRTHRESH |
R |
– |
Propagation factor |
BADINPDQ |
S |
– |
Data quality file bits to reject |
CRMASK |
B |
– |
Flag CR-rejected pixels in input files? |
CCDCHIP |
S |
– |
CHIP to which this conversion applies |
Selection Criteria: Selection is dependent on the DETECTOR keyword only. The appropriate table row gets selected for use in the calacs task acsrej, first based on the chip being processed (CCDCHIP), then on the number of images the original exposure was split into (CRSPLIT) and the exposure time of each CR-SPLIT image. The exposure time for each CR-SPLIT image is compared to MEANEXP from this table, and the row with the lowest MEANEXP without being less than the input image’s exposure time is selected. Once the appropriate row is selected, then the rest of the columns serve as the input parameters to control the detection algorithms.
Restrictions: Only for use with CCD detector data (DETECTOR != “SBC”). The SBC does not use this method as it rejects cosmic rays on input by pulse height discrimination.
Required Additional Keywords:
FILETYPE = "COSMIC RAY REJECTION"
10.3.6 MAMA Linearity Table (LIN): <unique name>_lin.fits
Description: The MAMA linearity table reference file (MLINTAB) provides the basic parameters for determining linearity in SBC MAMA images. In calacs, global and local nonlinearity is flagged in MAMA observations using the MLINTAB. Global nonlinearity refers to the entire ACS MAMA detector, while local nonlinearity refers to an individual detector pixel.
Format: Table 10-6 defines the MLINTAB table columns. Although there is only one MAMA detector within ACS, the first column specifies the detector name. The global limit given in the GLOBAL_LIMIT column refers to the total counts/sec for the entire image at which the data is affected by greater than 10% non-linearity. Calacs will attempt to correct for non-linearity up to this limit using the non-linearity constant given in the column TAU. Local non-linearity for some pixels can occur even when the global limit is not exceeded. Each pixel found to exceed the limit given in the column LOCAL_LIMIT is marked as nonlinear in the DQ file out to a radius from the pixel given in the EXPAND column.
Table 10-6. MAMA Linearity Table (LIN), <unique name>_lin.fits
Column Name |
Data Type |
Units |
Description |
|---|---|---|---|
DETECTOR |
CH*10 |
– |
Name of MAMA detector used (SBC) |
GLOBAL_LIMIT |
D |
Counts/sec |Count rate resulting in 10% global nonlinearity |
|
LOCAL_LIMIT |
D |
Counts/sec/pixel |
Count rate resulting in 10% local nonlinearity |
TAU |
D |
S |
Time constant in global nonlinearity expression |
EXPAND |
R |
Pixel |
Radius in pixels |
PEDIGREE |
CH*67 |
– |
How this row was created (DUMMY, GROUND) |
DESCRIP |
CH*67 |
– |
Short note describing this row |
Selection Criteria: Selection is dependent on the DETECTOR keyword only.
Restrictions: Only for use with SBC MAMA observations.
Required Additional Keywords:
FILETYPE = "LINEARITY"
10.3.7 Photometry and Throughput Table (PHT): <unique name>_pht.fits
Note: Photometry and throughput table referece files are no longer used for ACS data calibration, and have been replaced by the IMPHTTAB (see section 10.3.8).
Description: The photometry and throughput table reference file (PHOTTAB) provides the calibrated throughput for every filter combination used for ACS observations. Photometry on ACS observations requires a transformation from DN, measured in the image, to flux units. The STSDAS package synphot has a task called bandpar which can provide the parameters for that transformation; namely, PHOTFLAM, PHOTZPT, PHTOBW, and PHOTPLAM.
Format: Table 10-7 defines the PHOTTAB table columns. This table is selected by DETECTOR, so every row in the table should be applicable to the observation. The columns FILTER1 and FILTER2 give the filter combinations used for that detector, and the row that has the same combination as used in the observation is selected for use in calacs. The calibrated throughputs are stored as arrays of NELEM elements in the WAVELENGTH and THROUGHPUT columns, forming what is commonly referred to as a 3-D table.
Table 10-7. Photometry and Throughput Table (PHT), <unique name>_pht.fits
Column Name |
Data Type |
Units |
Description |
|---|---|---|---|
FILTER1 |
– |
– |
Name of Filter1 used for observation |
FILTER2 |
– |
– |
Name of Filter2 used for observation |
NELEM |
I |
– |
Number of elements |
WAVELENGTH |
R[NELEM] |
Angstroms |
Wavelength at which throughput is measured |
THROUGHPUT |
R[NELEM] |
– |
Number of wavelengths in throughput array |
PEDIGREE |
CH*67 |
– |
How this row was created (DUMMY, GROUND) |
Selection Criteria: Selection is dependent on the DETECTOR keyword only. Table rows are selected by FILTER1 and FILTER2.
Restrictions: None.
Required Additional Keywords:
FILETYPE = "PHOTOMETRY"
10.3.8 Photometry Keyword Table (IMP): <unique name>_imp.fits
Description: The photometry keyword table reference file (IMPHTTAB) contains pre-computed values of the photometry keywords to determine the total throughput of an observing mode. The IMPHTTABs are generated by mkimphhtab in reftools.
Calacs originally used the photometry and throughput table (see section 10.3.7), which was replaced by on-the-fly calls to PySynphot to determine photometry header keyword values. This IMPHTTAB table replaces the calls to PySynphot by providing measurements of the inverse sensitivity, pivot wavelength, and bandwidth at fixed times, between which calacs then interpolates. This provides time-dependent sensitivity information for all three ACS detectors.
Format: Table 10-8 defines the IMPHTTAB table columns for the HRC, WFC and SBC. Each table contains three extensions: PHOTFLAM, PHOTPLAM and PHOTBW. PHOTFLAM is the inverse sensitivity conversion factor measured in erg/cm²/Å/e¯. PHOTPLAM is the pivot wavelength measured in Angstroms. PHOTBW is the RMS bandwidth of filter plus detector. See section 14.1.3 for more information on the time dependent columns in the IMPHTTAB.
Table 10-8. Photometry Keyword File (IMP), <unique name>_imp.fits
HRC and WFC
Extension |
Extension Name |
Column Names |
|---|---|---|
0 |
Primary Header |
|
1 |
PHOTFLAM |
OBSMODE, DATACOL, PHOTFLAM, PHOTFLAM1, PHOTFLAM2, PAR1NAMES, PAR2NAMES, PAR1VALUES, PAR2VALUES, NELEM1, NELEM2, PEDIGREE, DESCRIP |
2 |
PHOTPLAM |
OBSMODE, DATACOL, PHOTPLAM, PHOTPLAM1, PHOTPLAM2, PAR1NAMES, PAR2NAMES, PAR1VALUES, PAR2VALUES, NELEM1, NELEM2, PEDIGREE, DESCRIP |
3 |
PHOTBW |
OBSMODE, DATACOL, PHOTBW, PHOTBW1, PHOTBW2, PAR1NAMES, PAR2NAMES, PAR1VALUES, PAR2VALUES, NELEM1, NELEM2, PEDIGREE, DESCRIP |
SBC
Extension |
Extension Name |
Column Names |
|---|---|---|
0 |
Primary Header |
|
1 |
PHOTFLAM |
OBSMODE, DATACOL, PHOTFLAM, PHOTFLAM1, PAR1NAMES, PAR1VALUES, NELEM1, PEDIGREE, DESCRIP |
2 |
PHOTPLAM |
OBSMODE, DATACOL, PHOTPLAM, PHOTPLAM1, PAR1NAMES, PAR1VALUES, NELEM1, PEDIGREE, DESCRIP |
3 |
PHOTBW |
OBSMODE, DATACOL, PHOTBW, PHOTBW1, PAR1NAMES, PAR1VALUES, NELEM1, PEDIGREE, DESCRIP |
Selection Criteria: Selection is dependent on the DETECTOR keyword only.
Restrictions: None.
Required Additional Keywords:
FILETYPE = "IMAGE PHOTOMETRY TABLE"
10.3.9 Image Distortion Coefficients Table (IDC): <unique name>_idc.fits
Description: The image distortion coefficients table reference file (IDCTAB) contains the distortion solution in the form of polynomials, as well as reference positions and size information. The geometric distortion is filter dependent and for each calibrated filter, there are unique geometric distortion coefficients. The IDCTAB is principally designed to support the AstroDrizzle package.
Format: Table 10-9 defines the IMPHTTAB table columns. CRDS maintains a structure which allows multiple instrument configurations to point to a single reference file or table. Because of this, the value of FILTER1 or FILTER2 in the header will sometimes take the value “ANY.” In addition to the normal keywords, the table header must contain NORDER, an integer giving the order of the polynomial fit, and PARITY, which will always be –1 for ACS. The number of coefficients in the table row depends on NORDER and is equal to (NORDER+1)(NORDER+2)/2. There can be sets of coefficients for DIRECTION = FORWARD, which converts the distorted image to an undistorted version, and for DIRECTION = INVERSE, which transforms the corrected image to the distorted view.
Table 10-9. Image Distortion Table (IDC), <unique name>_idc.fits
Column Name |
Data Type |
Units |
Description |
|---|---|---|---|
DETCHIP |
I |
– |
Chip number, 1 or 2 |
DIRECTION |
CH*8 |
– |
FORWARD or INVERSE |
XSIZE |
I |
– |
Size in X direction of final output image |
YSIZE |
I |
– |
Size in Y direction of final output image |
XREF |
R |
– |
X pixel position of reference point |
YREF |
R |
– |
Y pixel position of reference point |
V2REF |
R |
– |
Matching V2 position of reference point |
V3REF |
R |
– |
Matching V3 position of reference point |
SCALE |
R |
– |
Linear dimension in arcsec of square output image pixel |
CX10 |
R |
– |
First distortion coefficient |
… |
… |
– |
Further coeffcicents |
CXnn |
– |
– |
Last coefficient in X direction |
CY10 |
– |
– |
First coefficient in Y direction |
… |
R |
– |
Further coefficients |
Cynn |
R |
– |
Last coefficient in Y direction |
PEDIGREE |
CH*67 |
– |
How this row was created (DUMMY, GROUND) |
DESCRIP |
CH*67 |
– |
Short note describing this row |
Selection Criteria: Selection is dependent on the DETECTOR keyword only.
Restrictions: None.
Required Additional Keywords:
FILETYPE = "DISTORTION COEFFICIENTS"
10.3.10 Synphot Tables (SYN): <compname_version>_syn.fits
Description: Synphot table reference files are quantum efficiency curves, with throughput as a function of wavelength. Several component throughput tables (THRUPUT) exist for various ACS configurations.
Note: these files are still available and used within PySynphot for reference information, however they are not used by **calacs for photometry keyword population.**
Format: Synphot THRUPUT files take on various formats depending on configuration.
Selection Criteria: Selection is dependent on the COMPTAB and GRAPHTAB tables (section 10.3.11), rather than on any keywords.
Restrictions: None.
Required Additional Keywords:
FILETYPE = "CRTHROUGHPUT"
10.3.11 Master Component Lookup Table (TMC): (<uniqname>_tmc.fits)
Description: The master component lookup table reference file (TMCTAB) contains a listing of each synphot throughput file used for all of HST’s instruments. Any updates to a throughput file will require the same version number update to the TMCTAB. For example acs_f330w_003_syn.fits updates to acs_f330w_004_syn.fits.
Note: these files are still available and used within PySynphot for reference information, however they are not used by calacs for photometry keyword population.
Selection Criteria: Selection is dependent on the USEAFTER keyword only for all instruments.
Restrictions: None.
Required Additional Keywords:
FILETYPE = "CRCOMPLIST"
10.3.12 Graph Table (TMG) (<uniqname>_tmg.fits)
Description: The graph table reference file (TMGTAB) instructs synphot on exactly which of the synphot THRUPUT files listed in the COMPTAB are to be used in calculations for a given detector and filter combination.
Note: these files are still available and used within PySynphot for reference information, however they are not used by calacs for photometry keyword population.
Selection Criteria: Selection is dependent on the USEAFTER keyword only for all instruments.
Restrictions: None.
Required Additional Keywords:
FILETYPE = "CRGRAPH"