Section 11 Wide Field Camera 3

Observations made with the Wide Field Camera 3 are processed by the task calwf3, which makes use of the calibration files described in this chapter. More details about the use of the calibration files in calwf3 may be found in the WFC3 AV-03 document, ‘WFC3 Science Data Calibration Requirements’ (Bushouse 2001), as well as the WFC3 Data Handbook (Rajan et. al 2010).

11.1 File Formats and Conventions

Continuing the style of STIS, NICMOS, and ACS, all WFC3 science and calibration reference files (hereafter, reference files) are FITS files with image or table extensions. All image data resides in the image extensions. The FITS primary data unit is always empty, as indicated by the ‘NAXIS=0’ keyword setting in the primary header. The primary header contains all keywords not specific to individual extensions. Keywords specific to a particular extension are contained in the header of the extension. Current lists of WFC3 FITS header keywords are given in Section 11.6.

WFC3 has two detectors known as the UVIS channel and the IR channel, distinguished by the keyword DETECTOR, which may take the values ‘UVIS’ and ‘IR.’ The data from WFC3 exposures is organized into one or more imsets within a single FITS file. The image extensions that make up each imset are referred to by name according to the value of the EXTNAME keyword in each extension header.

WFC3 UVIS data imsets consist of three image extensions, with EXTNAMEs of ‘SCI’, ‘ERR’, and ‘DQ’. Like NICMOS, the WFC3 IR data imsets consist of five image extensions, with names of ‘SCI’, ‘ERR’, ‘DQ’, ‘SAMP’, and ‘TIME.’ The SCI extensions contain the data from readouts of the detector. The ERR extensions contain estimates of the statistical errors or uncertainties at each pixel. The DQ extensions contain data quality flags for each pixel, using 16-bit (short integer) encoding. The current list of WFC3 DQ flag value assignments is given in Table 2.5 of the WFC3 Data Handbook. The IR SAMP extensions contain the number of non-destructive readouts (or samples) used for each pixel in the SCI image. Similarly, the IR TIME extensions contain the total integration time (in units of seconds) at each pixel.

Local STScI conventions allow for images containing a constant value in all pixels to be stored as an empty FITS data array, indicated by NAXIS=0 in the image extension header. In these cases the dimensions of the constant array are stored in the NPIX1 and NPIX2 image extension header keywords. The constant pixel value is stored in the PIXVALUE extension header keyword.

The WFC3 UVIS focal plane array is composed of two Marconi CCDs, each 2051 by 4096 pixels. UVIS observation data and corresponding reference images contain two imsets in a single FITS file, with one imset per CCD. The FITS image extension headers contain the keyword ‘CCDCHIP’, which takes the value 2 for imset 1 and the value 1 for imset 2, and is used to identify the origin of the data in each imset. Serial physical and virtual overscan regions, as well as parallel virtual overscan regions, lead to raw images that are somewhat larger than the 2051 x 4096 pixel active area of the CCDs. Some of the calibration reference images used for UVIS image processing include the overscan pixels, while others do not. These are noted in the detailed discussions of each reference image in Section 11.4. The WFC3 IR detector is 1024 x 1024 pixels in size. These dimensions include a 5 pixel wide strip on each edge of the detector that is composed of reference pixels. Thus the active imaging area of the detector has dimensions 1014 x 1014 pixels. The raw IR science images and all IR calibration reference images include the reference pixels and therefore always have dimensions of 1024 x 1024 pixels. Some of the reference images are constructed so as to not affect the reference pixels when they are applied to the science data. This is accomplished by having the reference images contain values of zeros or ones for the reference pixels, as appropriate. These are noted in the detailed discussions of each reference image in Section 11.4. Like NICMOS, a WFC3 IR exposure is composed of multiple non-destructive readouts of the detector. The data from all readouts is stored in a single FITS file, in multiple imsets.

11.2 WFC3 Calibration Reference Files

11.2.1 Reference File Naming Conventions

The reference files share the same format and structure as the WFC3 science image datasets. The reference files stored in the STScI Calibration Data Base System (CDBS) have names of the form <uniquename>_xyz.fits where <uniquename> is a nine character unique name, the last character of which will be an ‘i’ for all WFC3 reference files. The leading eight characters are based on the date and time when the file was created. The suffix ‘xyz’ represents the type of calibration file and will be one of the strings such as ‘bia’, ‘drk’, etc, the meaning of which is given in the following sections.

11.2.2 Reference File Keyword Conventions

The headers of WFC3 reference files follow the generic WFC3 science data file headers as described in Section 11.6 and defined in STScI ICD-19.

Observation-specific keywords may be omitted from reference file headers. The three keywords DESCRIP, PEDIGREE, and USEAFTER are only contained in reference file headers and not in science files.

The keyword FILETYPE is used quite differently in reference files and is specified below for each type of file. Each string must exactly match the values specified and will be checked before being accepted by CDBS. 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 count images and should normally have the value 1 second (for the UVIS channel). 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 reference file header; unneeded keywords are simply ignored.

The DESCRIP keyword contains a brief description of the data. More extensive information should be supplied in the load files used when the reference files are installed in CDBS. It may be convenient to keep the same information as HISTORY lines in the file header. PEDIGREE can have the string values DUMMY, GROUND, or INFLIGHT. If the value DUMMY is present, calwf3 will skip the related calibration step even if the header keyword switch controlling that step 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.

Table 11-1. Common Required Header Keywords

Keyword Possible Values or Example Notes
DESCRIP Brief description of the file contents. For example: “F550W flat created from WFC3/UVIS cycle 17 data—————-“ Must be exactly 67 characters long. Appending dashes to reach 67 characters is common.
PEDIGREE DUMMY GROUND INFLIGHT dd/mm/yyyy dd/mm/yyyy If DUMMY is set, calwf3 wil ignore the relevent calibration step. Use GROUND for reference files created from ground testing data. If INFLIGHT is set, then the dates of the earliest and latest data used in the construction of the reference file must also be given.
USEAFTER “Jan 01 2010” Observations collected after this date will have this reference file applied to them, superceding any other reference file with the same selection parameters but an earlier USEAFTER date.
COMMENT “reference file created by S. Baggett” Contains the name of the person who created the file
HISTORY catch-all that can contain any pertinent information Should contain the name and version of the software used to create the file, a list of the observations/datasets/models used, and brief description of how the file is different from the one it is replacing.

To support the operation of calwf3, some reference files require additional keywords. These keywords, along with the essential selection and control keywords, are described in the following sections for each reference file.

11.2.3 Bias Image File (BIA): <uniquename>_bia.fits

Description: The bias reference image consists of an image of the additive stationary pattern in the electronic zero point of the UVIS CCDs. The structure of the electronic bias is removed from science images by subtracting the bias reference image. For WFC3 UVIS science data, it is normally the case that bias subtraction will be performed before the data is combined for cosmic- ray rejection.

Format: The bias reference images are zero exposure time, full-frame images, complete with serial and parallel overscan regions. The bias image size varies depending on the on-chip binning mode, as follows:

  • 1 x 1 binning: 2070 x 4206 pixel image
  • 2 x 2 binning: 1035 x 2102 pixel image
  • 3 x 3 binning: 690 x 1402 pixel image

Bias images for each of the 2 CCDs that make up the full detector array are stored in 2 separate imsets in the bias file, similar to UVIS science data. The bias image, along with its associated error array, is assumed to be in units of DN (ie with no gain applied). Although the exposure time is not used by calwf3, the EXPTIME keyword should be set to 0.0.

Selection Criteria: The appropriate bias reference file is selected by the DETECTOR, APERTURE, CCDAMP, CCDGAIN, BINAXIS1, and BINAXIS2 keywords.

Restrictions: This file is only used with DETECTOR=UVIS observations.

Required Additional Keywords:

FILETYPE = 'BIAS'

11.2.4 Dark Image File (DRK): <uniquename>_drk.fits

Description: The dark current reference image file consists of an image of the dark signal (i.e. the signal detected in the absence of photons from the sky). The dark reference image is subtracted from science images to remove the dark signal.

UVIS Format: For WFC3 UVIS observations the dark reference file is applied after the CCD overscan regions are trimmed from the input science image and therefore must have its overscan regions trimmed off as well. Furthermore, for UVIS CCD data, calwf3 multiplies the dark image by the exposure time and divides it by the gain before subtracting it from the science image. This requires the UVIS dark image to be in units of e^{-}/sec. The dark time is just the exposure time and does not include the idle time since the last flushing of the chip or the readout time. The UVIS dark image size varies depending on the on-chip binning mode, as follows:

  • 1 x 1 binning: 2051 x 4096 pixel image
  • 2 x 2 binning: 1026 x 2048 pixel image
  • 3 x 3 binning: 684 x 1364 pixel image

Dark images for each of the 2 CCDs that make up the full UVIS detector array are stored separately in 2 imsets in the dark file, like the UVIS science data.

IR Format: For WFC3 IR observations the dark reference files contain full-frame 1024 x 1024 pixel images. There are a total of 16 imsets in the IR dark reference files; one for each readout of a full MultiAccum sample sequence. calwf3 subtracts the dark current after zeroth read subtraction, meaning that the dark current reference file must also have the zeroth read subtracted from all subsequent reads. This implies that the zeroth read of the dark current reference files should contain all zeros in all pixels. The IR dark images are scaled to a detector gain of 1, but are not rescaled by exposure time. In other words, the dark current data and uncertainties should be in units of DN.

As with standard IR channel data, each imset of a dark current reference file contains 5 extensions. The first extension, labeled as SCI, contains the dark current signal values. These values are calculated on a pixel-by-pixel basis, as the sigma-clipped mean value of the input pixels. The second extension (ERR), contains the uncertainties associated with the values in the SCI extension. Currently, the ERR values are calculated as the sigma-clipped standard deviation of the input dark current signal values, divided by the square root of the number of input values used to calculated the SCI values. The third extension (DQ) contains the data quality flags associated with the dark current values. The only DQ flags that should be present in IR channel dark current files are 16 (hot pixels), and 128 (bad reference pixels, which include the outermost rows and columns of reference pixels). Other, more permanent flags, such as those for dead and unstable pixels, are contained in the bad pixel table reference file.

The fourth extension contains the SAMP array. For each pixel, this array lists the number of input values used to calculate the mean dark current value. For example, if 12 ramps are combined to calculate the mean dark current signal but there is a cosmic ray hit in pixel (500,500) in one of the ramps, then that cosmic ray affected signal is thrown out and the SAMP array at (500,500) will contain the value 11. The final extension of each imset is the TIME extension. This extension lists the exposure time associated with the given read of the sample sequence used to collect the data. All pixels in a given TIME extension should have the same value. In this way, if you wish to calculate the total exposure time that has gone into creating the dark current value in the SCI extension, you can multiply the SAMP array with the TIME array and create an array of total exposure times. NOTE: At the moment, no standard data reduction software (calwf3, opus, etc) use the SAMP or TIME arrays in any way.

IR dark reference files must also include the keyword NUMEXPOS in the primary header. This should be set to the number of imsets in the dark reference file, which is 16. Also present in the primary header must be a set of 16 keywords, named EXPOS_n, where n ranges from 1 to 16. These keywords give the exposure time of each of the 16 imsets in the reference file (i.e. EXPOS_n = EXPTIME from the [sci,n] extension). While this information is present in the extension headers of the reference file, it is also needed in the primary header for historical reasons.

The LTV1 and LTV2 keywords must also be correctly populated in the IR dark current reference files, in the headers of the SCI and ERR extensions, in order to prevent a calwf3 error during the zeroth read subtraction step. Appropriate LTV1 and LTV2 values for the four subarray sizes are as follows:

Table 11-2. LTV keyword values.

Subarray size (pixels) LTV1 LTV2
64 -470.0 -470.0
128 -438.0 -438.0
256 -374.0 -374.0
512 -246.0 -246.0

Selection Criteria:

UVIS: The appropriate dark reference file is selected by the DETECTOR, CCDAMP, APERTURE, BINAXIS1, BINAXIS2, and CHINJECT keywords.

IR: The appropriate dark reference file is selected by the DETECTOR, CCDAMP, CCDGAIN, SUBTYPE and SAMP_SEQ keywords.

Restrictions: None.

Required Additional Keywords:

FILETYPE = 'DARK'

11.2.5 Flat-Field Image Files

WFC3 can utilize up to three different flat-field images during calibration: the pixel-to-pixel flat (PFLTFILE), the delta flat (DFLTFILE), and the low-order flat (LFLTFILE). If more than one of the three types of flats is specified for a given science data set, each flat is applied in turn to the science data by calwf3.

11.2.5.1 Pixel-to-Pixel Flat Image File (PFL): <uniquename>_pfl.fits

Description: The PFLTFILE represents the relative variations in pixel-to-pixel sensitivity of the detector. These images contain the wavelength-dependent, high spatial frequency information about the uniformity of the detector response. This image is divided into the science images during the course of calibration.

Format: For WFC3 UVIS observations, the P-flat reference file is applied after the CCD overscan regions are trimmed from the input science image and therefore must have its overscan regions trimmed off as well. The UVIS P-flat image size varies depending on the on-chip binning mode, as follows:

  • 1 x 1 binning: 2051 x 4096 pixel image
  • 2 x 2 binning: 1026 x 2048 pixel image
  • 3 x 3 binning: 684 x 1364 pixel image

P-flat images for each of the 2 CCDs that make up the full UVIS detector array are stored separately in 2 imsets in the P-flat file, like the UVIS science data. For WFC3 IR observations the P-flat reference file is applied before the detector reference pixels are trimmed from the input science image and therefore are full-frame images with a size of 1024 x 1024 pixels. The reference pixels are populated with a value of 1 in the IR P-flat file. There is 1 imset in the IR P-flat file.

Note that only full-frame P-flat files are necessary. When processing subarray data, calfw3 extracts the appropriate subarray from the full frame flat.

Selection Criteria:

UVIS: The appropriate P-flat reference file is selected by the DETECTOR, CCDAMP, FILTER, BINAXIS1, and BINAXIS2 keywords.

IR: The appropriate P-flat reference file is selected by the DETECTOR, CCDAMP, and FILTER keywords.

Restrictions: None.

Required Additional Keywords:

FILETYPE = 'PIXEL-TO-PIXEL FLAT'

11.2.5.2 Delta Flat Image File (DFL): <uniquename>_dfl.fits

Description: The DFLTFILE consists of an image containing changes to the small-scale flat field contained in the PFLTFILE.

Format: For WFC3 UVIS observations, the D-flat reference file is applied after the CCD overscan regions are trimmed from the input science image and therefore must have its overscan regions trimmed off as well. The UVIS D-flat image size varies depending on the on-chip binning mode, as follows:

  • 1 x 1 binning: 2051 x 4096 pixel image
  • 2 x 2 binning: 1026 x 2048 pixel image
  • 3 x 3 binning: 684 x 1364 pixel image

D-flat images for each of the 2 CCD’s that make up the full UVIS detector array are stored separately in 2 imsets in the D-flat file, like the UVIS science data. For WFC3 IR observations the D-flat reference file is applied before the detector reference pixels are trimmed from the input science image and therefore are full-frame images with a size of 1024 x 1024 pixels. The reference pixels are populated with a value of 1 in the IR D-flat file. There is 1 imset in the IR D-flat file.

Selection Criteria:

UVIS: The appropriate D-flat reference file is selected by the DETECTOR, CCDAMP, FILTER, BINAXIS1, and BINAXIS2 keywords.

IR: The appropriate D-flat reference file is selected by the DETECTOR, CCDAMP, and FILTER keywords.

Restrictions: None.

Required Additional Keywords:

FILETYPE = 'DELTA FLAT'

11.2.5.3 Low-Order Flat Image File (LFL): <uniquename>_lfl.fits

Description: The LFLTFILE consists of a map of the large-scale variations in the sensitivity across the detector. This image contains the wavelength-dependent, low spatial frequency information about the uniformity of the detector. As such, this reference image usually gets stored as a subsampled image and expanded to match the science data when being applied by calwf3.

Format: For WFC3 UVIS observations, the L-flat reference file is applied after the CCD overscan regions are trimmed from the input science image and therefore must have its overscan regions trimmed off as well. L-flat images for each of the 2 CCDs that make up the full UVIS detector array are stored separately in 2 imsets in the L-flat file, like the UVIS science data.

For WFC3 IR observations the L-flat reference file is applied before the detector reference pixels are trimmed from the input science image and therefore must have its reference pixel regions intact. The reference pixels are populated with a value of 1 in the IR L-flat file. There is 1 imset in the IR L-flat file. The UVIS and IR L-flats are binned, full-frame images.

Selection Criteria:

UVIS: The appropriate L-flat reference file is selected by the DETECTOR, CCDAMP, and FILTER keywords.

IR: The appropriate L-flat reference file is selected by the DETECTOR, CCDAMP, and FILTER keywords.

Restrictions: None.

Required Additional Keywords:

FILETYPE = 'LARGE SCALE FLAT'

11.2.6 Shutter-Shading Image File (SHD): <uniquename>_shd.fits

Description: This reference file corrects a UVIS CCD image for the differential exposure time across the detector that results from the shutter travel time as it opens to start the exposure. Each pixel in the reference image gives the additional time that a given pixel was exposed above the nominal exposure time.

Format: This reference image is a subsampled, overscan-trimmed. Currently, these reference files are subsampled by a factor of 8 for each dimension, resulting in a 256 x 512 pixel image for each chip of the UVIS detector.

Selection Criteria: This reference file is selected by the DETECTOR keyword.

Restrictions: This file is used only with DETECTOR=UVIS observations.

Required Additional Keywords:

FILETYPE = 'SHUTTER SHADING'

11.2.7 Post-Flash Image File (FLS): <uniquename>_fls.fits

Description: This reference file corrects a UVIS CCD image for the signal added to an exposure by the postflash procedure. The scaled reference image (see below) is subtracted from the science exposure by calwf3.

Format: The postflash reference images are full-frame, including physical and virtual overscan regions. Furthermore, calwf3 multiplies the postflash image by the exposure time and divides it by the gain before subtracting it from the science image. This requires the postflash image to be scaled to an exposure time of 1 second and a gain of 1. There are separate postflash images for each on-chip CCD binning mode, with sizes as follows:

  • 1 x 1 binning: 2051 x 4096 pixel image
  • 2 x 2 binning: 1026 x 2048 pixel image
  • 3 x 3 binning: 684 x 1364 pixel image

Postflash images for each of the 2 CCDs that make up the full UVIS detector array are stored separately in 2 imsets in the postflash file, like the UVIS science data.

Selection Criteria: This reference file is selected by the DETECTOR, CCDAMP, SHUTRPOS, FLASHCUR, BINAXIS1, and BINAXIS2 keywords.

Restrictions: This file is used only with DETECTOR=UVIS observations.

Required Additional Keywords:

FILETYPE = 'POST FLASH'

11.2.8 Linearity Correction File (LIN): <uniquename>_lin.fits

Description: The linearity correction file contains a set of coefficients for each pixel that detector. The observed response of the detector is represented by two regimes. At count levels below the saturation threshold the detector response deviates from the incident flux in a manner that can be adequately represented by a second-order polynomial. At high count levels – as saturation sets in – the response becomes highly nonlinear and is not correctable to sufficient scientific accuracy.

The two regimes are defined and separated by the saturation threshold – the level beyond which no useful data can be extracted. Currently this saturation threshold is defined on a pixel-by-pixel basis as the signal level at which the data deviate from linearity by 5%. For lower points, the following correction is used:

I' = (c_0 + c_1\*I + c_2\*I_2 + c_3\*I_3) \* I

where I is the uncorrected SCI image value, I’ is the corrected value, and c_0, c_1, c_2, and c_3 are the linearity coefficients for a given pixel. The order of the polynomial correction is a tunable parameter in the correction file. Therefore, the correction equation above can be extended to include higher order coefficients. The current correction in place for the IR channel matches the equation above.

The uncertainties and covariance values associated with the coefficients above are collected from the polynomial fitting routine as the equation above is fit to each pixel’s signals. Standard error propagation dictates that the uncertainty associated with the corrected signals then becomes:

\sigma^{'} = \sqrt{g^T V g}

where g is the vector of partial derivatives of I with respect to the coefficients c_0 through c_3 and V is the variance-covariance matrix of the set of coefficients.

V = \left(\begin{matrix} e_{0} & e_{01} & e_{02} & e_{03} \\
                    e_{10} & e_{1} & e_{12} & e_{13} \\
                    e_{20} & e_{21} & e_{2} & e_{23} \\
                    e_{30} & e_{13} & e_{23} & e_{3} \end{matrix}\right)

Each of the individual elements of V are saved in a separate extension in the non-linearity reference file, as shown in Table 11-3 below.

Format: This file departs from the standard format of SCI, ERR, DQ image extensions. The linearity coefficients are stored in floating-point image extensions with EXTNAME=COEF and EXTVER values ranging from 1 to 4. The variance, or error, values are stored in ten floating- point image extensions with EXTNAME=ERR and EXTVER values of 1 to 10. Note that the number of extensions for coefficients and variances will change based on the order of the polynomial used. The number of extensions needed for variances is equal to the number of coefficients, while the number of extensions needed for covariances is equal to:

Num Covars = \sum_{1}^{N-1}x

where N is the number of coefficients.

Data quality flags are stored, as usual, in a short-integer image extension with EXTNAME=DQ and EXTVER=1. The saturation threshold values (in units of DN) are stored in a floating-point image extension with EXTNAME=NODE and EXTVER=1.

In addition to the above data, the LIN reference file also contains two floating-point image extensions that store a ‘super zero read’ image and its associated statistical error image. These image extensions are designated by EXTNAME=ZSCI, EXTNAME=ZERR, and EXTVER=1. The ZSCI image is the average of large number of MuliAccum zeroth read images and is used by calwf3 to estimate the amount of signal that may be present in the zeroth read of the science image that is being calibrated. A typical file organization is shown in Table 11-3.

Table 11-3. Linearity File Format

Ext. No. EXTNAME EXTVER BITPIX Contents
0 N/A N/A 8 Primary header with null data array
1 COEF 1 -32 Linearity coefficient c0
2 COEF 2 -32 Linearity coefficient c1
3 COEF 3 -32 Linearity coefficient c2
4 COEF 4 -32 Linearity coefficient c3
5 ERR 1 -32 Variance e0
6 ERR 2 -32 Variance e1
7 ERR 3 -32 Variance e2
8 ERR 4 -32 Variance e3
9 ERR 5 -32 Covariance e01
10 ERR 6 -32 Covariance e12
11 ERR 7 -32 Covariance e23
12 ERR 8 -32 Covariance e02
13 ERR 9 -32 Covariance e13
14 ERR 10 -32 Covariance e03
15 DQ 1 16 Data quality flags
16 NODE 1 -32 Saturation threshold
17 ZSCI 1 -32 Super zero read science image
18 ZERR 1 -32 Uncertainties of super zero read

Selection Criteria: This reference file is selected by the DETECTOR keyword.

Restrictions: This file is used only with DETECTOR=IR observations.

Required Additional Keywords:

FILETYPE = 'LINEARITY COEFFICIENTS'

11.2.9 Detector-to-Image Correction File (D2I): <uniquename>_d2i.fits

Description: The D2IMFILE reference file is a 2-D look-up table that contains astrometric corrections for shifts induced by the lithographic-mask pattern that was imprinted on the UVIS detector during the manufacturing process. This correction table is used in coordinate transformations prior to applying the large-scale polynomial geometric solution (IDCTAB). The look-up table is incorporated by running updatewcs (via AstroDrizzle) with the filename specified in the D2IMFILE keyword in the primary image header, which will then be attached to the image as a fits extension of type ‘D2IMARR’ (four extensions total, two for each chip and dimension). Each element of the 32x17 table gives the astrometric xy shift in pixels to apply at a particular location on the detector. The version of IRAFX dated May 20, 2013 was updated to allow AstroDrizzle to interpolate across a 2-D table grid, and hence only this IRAFX version (and later) can apply the D2IMFILE corrections.

Table 11-4 Detector-to-Image File Format

Ext. No. EXTNAME TYPE BITPIX CARDS DIMENSIONS
0 PRIMARY PRIMARY 16 51 ( )
1 DX ImageHDU -32 14 (64, 32)
2 DY ImageHDU -32 14 (64, 32)
3 DX ImageHDU -32 14 (64, 32)
4 DY ImageHDU -32 14 (64, 32)

Selection Criteria: This reference file is selected by the DETECTOR keyword.

Restrictions: This file is only used with DETECTOR=UVIS observations where DRIZCORR is not set to OMIT.

Required Additional Keywords:

FILETYPE = 'UVIS D2I FILE'

11.2.10 Non-polynomial Filter Dependent Distortion File (NPL): <uniquename>_npl.fits

Description: The NPOLFILE is a 2-D look up table that contains the non-polynomial filter-dependent part of the distortion correction. This correction table is bi-linearly interpolated by the STSDAS DrizzlePac/AstroDrizzle software in the STScI On-The-Fly Reprocessing. These files help correct the astrometric irregularities in the WFC3/UVIS filters that introduce fine-scale astrometric errors.

Table 11-5 Non-polynomial Filter Dependent Distortion File Format

Ext. No. EXTNAME TYPE BITPIX CARDS DIMENSIONS
0 PRIMARY PRIMARY 16 51 ( )
1 DX ImageHDU -32 14 (64, 32)
2 DY ImageHDU -32 14 (64, 32)
3 DX ImageHDU -32 14 (64, 32)
4 DY ImageHDU -32 14 (64, 32)

Selection Criteria: This reference file is selected by the DETECTOR and FILTER keywords.

Restrictions: This file is only used with DETECTOR=UVIS observations where DRIZCORR is not set to OMIT.

Required Additional Keywords:

FILETYPE = 'DXY GRID'

11.3 WFC3 Calibration Reference Tables

Reference tables are treated slightly differently from reference images by CDBS. For the WFC3 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 new rows that did not appear in previous tables. Table headers are quite simple, only needing the keywords shown in Table 11-4 below. The PEDIGREE and DESCRIP keywords appear in the table rows, since each row may have a different pedigree.

Table 11-6. WFC3 Reference Table Header

Keyword Name Default Value Comment
SIMPLE T FITS standard
BITPIX 16 Bits per pixel
NAXIS 0 Number of axes
IRAF-TLM   Time of last modification
EXTEND T There may be standard extensions
ORIGIN   FITS file originator
DATE   Date FITS file was generated
FILENAME   Name of file
TELESCOP HST Telescope used to acquire data
INSTRUME WFC3 Instrument used to acquire data
DETECTOR   Detector used to acquire data
FILETYPE   Calibration file type

11.3.1 Analog-to-Digital Table (A2D): <uniquename>_a2d.fits

Description: This table 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 amps used, and, typically, the exposure time of the observation.

Format: Table 11-7 defines the A2D table columns.

Table 11-7. Analog-to-Digital (A2D) Table, <uniquename>_a2d.fits

Column Name Data Type Units Description
CCDAMP CH*4 CCD amplifier readout configuration
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: This reference table is selected by the DETECTOR keyword, and rows within the table are selected by CCDCHIP, CCDAMP, and CCDGAIN.

Restrictions: This file is used only with DETECTOR=UVIS observations.

Required Additional Keywords:

FILETYPE = 'ANALOG-TO-DIGITAL'

11.3.2 Bad Pixel Table (BPX): <unique name>_bpx.fits

Description: This reference file maintains a record of all known bad pixels for each WFC3 detector. The goal of the bad pixel table is to list all of the pixels which are bad on long-term timescales. Therefore, hot pixels are not recorded in the bad pixel table, but are rather recorded in the dark current reference files. In the IR channel, types of bad pixels recorded in the bad pixel table include dead (4), deviant zeroth read (8), unstable (32), and bad in flat (512). In the UVIS channel bad pixel types include dead (4) and bad in reference file (512). Other types of bad pixels are flagged during various steps within the calfw3 pipeline.

It is the job of the BPIXTAB to maintain the list of bad pixels applicable for a given time period. The DQ values associated with each pixel listed in the BPIXTAB are written to the DQ image extensions of the science data being processed by calwf3 and are combined with any previously existing DQ values. Bad pixels due to telemetry errors will be flagged during Generic Conversion.

Format: The positions of bad pixels are stored as pixel lists using the columns defined in Table 11-8. As for the image keywords, the not applicable table entries show ‘N/A’ or ‚Äì999 depending on the data type. Some values are only marked during other calwf3 processing steps (such as cosmic-ray rejection). Note that the locations of bad pixels, given in the PIX1 and PIX2 columns are given in reference and overscan pixel-trimmed coordinates. For example, the UVIS pixel in the lower left corner of the detector would be listed in the bad pixel table as (-24,1). Similarly, the pixel in the lower left corner of the IR channel would be listed in the bad pixel table as (-4,-4).

For the UVIS detector, if a bad pixel at (x,y) is part of a bad row or column, the entire group of bad pixels can be identified by setting PIX1 and PIX2 equal to x and y respectively, and then making the LENGTH entry equal to the number of consecutive bad pixels along the row/column, and using the AXIS entry to specify whether the consecutive bad pixels stretch along a row (2) or column (1).

In addition, for the UVIS, any bad row extending across the amp boundary in the center must be broken into two separate entries in the bad pixel table, once for each amp. This is necessary in order to avoid having calwf3 mistakenly count the virtual overscan pixels between chips as bad.

As pixels in the IR channel rarely go bad in groups along a row or column, bad pixels in the IR bad pixel table will largely be listed individually, with the LENGTH entry set equal to 1. Our current strategy is to have the bad pixel table list only pixels that are permanently bad (ie unusable for science) in some way. Other types of ‘bad’ pixels, such as those with abnormally high dark current, will be flagged in other reference files.

CCDAMP and CCDGAIN columns are optional. PEDIGREE and DESCRIP columns are required, but not used when the bad pixel table is applied by calwf3.

Table 11-8. Bad Pixel Table (BPX), <unique name>_bpx.fits

Column Name Data Type Units Description
CCDAMP CH*4 CCD amplifier readout configuration
CCDGAIN S Electrons/DN Commanded gain
CCDCHIP S CHIP to which these data apply
PIX1 S Pixel X position of bad pixel list
PIX2 S Pixel Y position of bad pixel list
LENGTH S Pixel Number of bad pixels in this list
VALUE S DQ value of bad pixels
AXIS S Bad pixels extend along this axis
PEDIGREE CH*67 GROUND/DUMMY/INFLIGHT
DESCRIP CH*67 Short note describing this row

Selection Criteria: Bad pixel tables are selected by DETECTOR (UVIS or IR). Table rows are selected by CCDCHIP, CCDAMP, and CCDGAIN.

Restrictions: None.

Required Additional Keywords:

FILETYPE = 'BAD PIXELS'
SIZAXIS1 = [npix]             / axis 1 size of bad pixel          array
SIZAXIS2 = [npix]             / axis 2 size of bad pixel          array

The FILETYPE keyword must appear in the primary header of the reference table, while the SIZAXIS1 and SIZAXIS2 keywords must appear in the table extension header.

11.3.3 CCD Characteristics Table (CCD): <unique name>_ccd.fits

Description: Up to four detector amplifiers can be used for any given observation and each amplifier has its own read-out characteristics. However, only a single value for these characteristics can be commanded by the observer. This table (with columns as defined in Table 11-7) provides the conversion from the commanded values to the calibrated values for each amp. These calibrated values are then used during processing by calwf3 to insure that a pixel read out by an amp has been properly calibrated for that amp’s readout characteristics. The characteristics affected are readout noise (READNSE), A-to-D gain (ATODGN), and bias level (CCDBIAS).

Format: The table contains one row for each amp 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), the commanded bias level offset (CCDOFST), and the bin sizes of the pixels read out (BINAXIS). Measured bias, gain, and readnoise numbers (CCDBIAS, CCDGAIN, and READNSE respectively) associated with each readout configuration are also provided.

The AMPX and AMPY keywords are used to describe the area of the chip read out through each amplifier for a given readout configuration. Each of the two chips in the UVIS detector can be read out through either one or two amplifiers. For a given chip, the AMPX keyword specifies the column that is the dividing line between the areas read out by the two amplifiers. More specifically, AMPX lists the column number of the last column to be read out by the first amplifier. Column numbers are given in terms of trimmed detector coordinates (ie ignore overscan columns) and are indexed to 1 rather than 0. This means that column numbers for each chip run from 1 to 4096.

As an example, take the case of a standard unbinned full-frame readout where each chip is read out by two amplifiers (one for the left half and one for the right half). The AMPX keyword value here will be 2048. This means that for chip 2, columns 1 through 2048 will be read out through amplifier A, while columns 2049 through 4096 will be read out through amplifier B. For the case where we wish all of chip 2 to be read out through amp A, the AMPX keyword value is set to 4096 implying that columns 1 through 4096 (i.e. all columns) will be read out through amp A. In the opposite case, where we wish all of chip 2 to be read out through amp B, the AMPX keyword is set to 0, specifying that no rows are read out through amp A and that amp B begins reading at column 1.

In the case of the IR channel, there are many fewer readout modes. Each quadrant of the detector can only be read out through its associated amplifier. Unlike the UVIS channel, the IR channel column number is given in units of raw detector coordinates (i.e. including reference pixels) indexed to 1. Therefore, AMPX always has a value of 512 in the IR CCDTAB file.

The AMPY keyword works in a similar fashion but in the other dimension. AMPY specifies the dividing row number between amplifier readout areas. In both UVIS and IR channels, we can only use one amplifier to read out all rows of a chip or quadrant, therefore AMPY always has a value of 0. AMPX and AMPY values are used throughout calwf3 to determine the amplifier readout pattern and apply the correct read noise, gain, and bias level to each pixel.

The CCDTAB file also contains the SATURATE column. This entry contains the signal level in DN at which pixels in each readout mode reach saturation. This column is ignored during the processing of IR data. calwf3 uses this column in the calibration of UVIS data, where a single saturation level is used for all pixels. Pixels with signal values above this threshold are flagged as saturated. Unlike in the UVIS channel, each pixel in the IR channel has its own independent saturation level. These saturation levels are recorded in the non-linearity correction file, and applied to IR channel data during the non-linearity correction step.

Table 11-9. CCD Characteristics Table (CCD), <unique name>_ccd.fits

Column Name Data Type Units Description
CCDAMP CH*4 CCD amplifier readout configuration
CCDCHIP S Chip to which these data apply
CCDGAIN S Electrons/DN Commanded gain
CCDOFSTA S Commanded bias for amp A of CCD
CCDOFSTB S Commanded bias for amp B of CCD
CCDOFSTC S Commanded bias for amp C of CCD
CCDOFSTD S Commanded bias for amp D of CCD
CCDBIASA R Actual bias for amp A of CCD
CCDBIASB R Actual bias for amp B of CCD
CCDBIASC R Actual bias for amp C of CCD
CCDBIASD R Actual bias for amp D of CCD
BINAXIS1 S Pixels Commanded bin size for axis 1
BINAXIS2 S Pixels Commanded bin size for axis 2
ATODGNA R Electrons/DN Actual gain for amp A used for readout
ATODGNB R Electrons/DN Actual gain for amp B used for readout
ATODGNC R Electrons/DN Actual gain for amp C used for readout
ATODGND R Electrons/DN 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 Pixel First column affected by second amp
AMPY S Pixel First row affected by second set of amps
SATURATE R DN Saturation threshold
PEDIGREE CH*67 How this row was created
DESCRIP CH*67 Short note describing this row

Selection Criteria: The CCD table is selected by DETECTOR. Table rows are selected by CCDCHIP, CCDAMP, CCDGAIN, CCDOFSTA, CCDOFSTB, CCDOFSTC, CCDOFSTD, BINAXIS1, and BINAXIS2.

Restrictions: None.

Required Additional Keywords:

FILETYPE = 'CCD PARAMETERS'

11.3.4 Overscan Region Table (OSC): <unique name>_osc.fits

Description: This table describes the overscan regions for each chip along with the regions to be used for determining the actual bias level of the observation. Each row corresponds to a specific configuration as given by the amps used (CCDAMP), the chip (CCDCHIP), and the on-chip binning mode (BINX, BINY).

The WFC3 UVIS detector images can contain up to four serial overscan regions (1 physical pre- scan and 1 virtual post-scan region associated with each of the 2 amps on each chip), requiring the specification of 4 trim regions in the X direction. Each UVIS detector chip also contains one parallel virtual overscan region. This requires the specification of at least 1 trim region in the Y direction, either at the top or bottom of <the image (depending on which chip is begin dealt with). See WFC3 ISR 2003-14 for details.

The WFC3 IR detector contains one reference pixel region on each of the four outer edges of the chip, requiring the specification of 2 trim regions in each of the X and Y directions of the images. See WFC3 ISR 2002-06 for details.

Format: The OSC table contains the columns of data listed in Table 11-10. NX and NY contain the total number of pixels in the X and Y directions of each chip, including overscan or reference pixels.

The columns TRIMX[1234] give the number of columns of image data to trim off the beginning, middle, and end of each row, while the corresponding TRIMY columns give the number of rows to trim off the top and bottom of each column. For example, in the case of a full-frame UVIS readout using 2 amplifiers per chip, the TRIMX[1,2,3,4] keywords have values of [25,25,30,30], and TRIMY[1,2] have values of [19,0] for chip 1. Chip 1 is read out through Amps A and B, and the four TRIMX values indicate that the first 25 columns should be trimmed off of the data read in through both. The first value of 25 above (TRIM1X1) corresponds to Amp A data, while the second (TRIMX2) applies to the Amp B data. Similarly, the first of the two ‘30’ values (TRIMX3) indicates that the final 30 columns read in through Amp A should be trimmed. The final value (TRIMX4) indicates that the final 30 columns read through Amp B should also be trimmed. See Figure 1 in WFC3 ISR 2003-14 for a schematic of this situation. Note that for chip 1, TRIMX1 and 2 do not always correspond to data read through Amp A. In the case where chip 1 is read out only through Amp B, the appropriate column numbers for Amp B should be placed in the TRIMX1 and 2 keywords, while the TRIMX3 and 4 keywords are set to 0 and ignored.

For each of the two chips that make up the UVIS detector, the bias level is determined within the overscan regions. For a each chip, the overscan regions to be used are specified using 4 pairs of beginning/ending column numbers. Following a similar pattern as the TRIMX keywords above, these 4 pairs correspond to the areas within the Amp A leading (physical), Amp B leading (physical), Amp A trailing (virtual), and Amp B trailing (virtual) overscan regions used to calculate the bias levels.

More specifically for chip 1, the first pair of numbers, given by the BIASSECTA1 and BIASSECTA2 values, provide the starting and ending column numbers of the Amp A leading overscan area to be used for bias calculation. BIASSECTB1 and BIASSECTB2 give the beginning and ending column numbers to be used in the Amp B leading overscan area. BIASSECTC1 and BIASSECTC2 refer to the beginning and ending column numbers to be used in the Amp A trailing overscan region. BIASSECTD1 and BIASSECTD2 contain column numbers for the Amp B trailing overscan region. The same pattern of keywords is used in chip 2, with Amp C and D values replacing those of Amp A and Amp B, respectively. As with the TRIM keywords above, the BIASSECT A and C keywords do not always correspond to data read through Amp A. In the case where chip 1 is read out entirely through Amp B, there will be no virtual overscan region at all. In this case, the two regions of physical overscan (on the left and right sides of the chip) should be defined using the BIASSECT A and B columns, while the C and D columns are set to 0.

Finally, the parallel virtual overscan regions on each chip are defined using the VX(1-4) and VY(1-4) keywords. Taken together, each VX,VY pair gives the coordinates of the beginning or ending point of one of the parallel overscan regions. For example, in the case where chip 1 is read out through 2 amplifiers, (VX1,VY1) provides the coordinates of the first pixel in the parallel overscan region that is read through Amp A. (VX2,VY2) gives the coordinates of the final point in the Amp A parallel overscan. Similarly, the parallel overscan region read out through Amp B is defined using the coordinates (VX3,VY3) and (VX4,VY4). The values for chip 2 when read out through 2 amplifiers are identical. For a 2 amplifier, unbinned readout, the four (VX,VY) coordinate pairs are (26,1), (2703,19), (2131,1) and (4181,19).

In the case where each chip is read out by only one amplifier, we need to define only one region of parallel overscan. In this case, the corners of the parallel overscan region are defined using (VX1,VY1) and (VX2,VY2). In the case of a full-frame unbinned observation, the coordinates used are (26,1) and (4181,19), respectively. The ‘3’ and ‘4’ versions of these keywords are set to zero in this case, and ignored.

The overscan region table is very complex and can be confusing. The best way to understand how each row of the table is set up is to open an existing table examine the values for each readout mode.

For the IR detector, the same keywords are used, but the situation is much simpler due to the limited number of readout modes. IR data are always read out through all 4 amplifiers and cannot be binned. With the 5 row and columns of reference pixels added to all IR data, the values of the keywords in the overscan region table are constant for all readout modes, except for the NX, NY, BIASSECTB1 and B2 columns, which vary with subarray size. In addition, for keywords refering to the X coordinates, such as TRIMX, quadrants 1 and 2 are lumped together and look at only a single keyword, as do quadrants 3 and 4. The same is true in the Y direction, with the two lower quadrants considered as a single chip, as are the two upper quadrants.

The values of TRIMX1 and 2 are both set to 5, as as both of TRIMY1 and 2. TRIMX3 and 4 are set to 0 and ignored. BIASSECTA1 and A2 are always set to 2 and 5, while BIASSECTB1 and B2 give contain values corresponding to the 5th-to-last and 2nd-to-last columns for each subarray size. Note that in the IR, the left-most and right-most columns (numbers 1 and 1024) are not used in the bias calcuation since they are a different type of reference pixel from the rest.

All coordinates and column and row numbers are specified in terms of the untrimmed image, are in units of binned pixels, and are indexed to one (ie for the IR, pixel values run from 1-1024).

Descriptions of each field are given in the table below. References to “amp 1” and “amp 2” can be taken to mean “Amp A” and “Amp B” for 2 apmlifier readouts of chip 1, but can refer to different amplifiers depending on readout mode.

Table 11-10. Overscan Region Table (OSC), <unique name>_osc.fits

Column Name Data Type Units Description
CCDAMP CH*4 CCD amplifier readout configuration
CCDCHIP S Chip to which these data apply
BINX S Pixels Commanded bin size for axis 1
BINY S Pixels Commanded bin size for axis 2
NX S Pixels Number of columns in image with overscan regions
NY S Pixels Number of rows in image with overscan regions
TRIMX1 S Pixels Number of columns to trim off beginning of each row
TRIMX2 S Pixels Number of columns to trim off end of each row
TRIMX3 S Pixels Number of columns (of virtual overscan) to trim off data read at end of row through first amp
TRIMX4 S Pixels Number of columns (of virtual overscan) to trim off data read through second amp (if used)
TRIMY1 S Pixels Number of rows to trim off beginning of each column
TRIMY2 S Pixels Number of rows to trim off end of each column
BIASSECTA1 S Pixel Beginning column for leading bias section of amp 1
BIASSECTA2 S Pixel Ending column for leading bias section of amp 1
BIASSECTB1 S Pixel Beginning column for leading bias section of amp 2
BIASSECTB2 S Pixel Ending column for leading bias section of amp 2
BIASSECTC1 S Pixel Beginning column for trailing bias section of amp 1
BIASSECTC2 S Pixel Ending column for trailing bias section of amp 1
BIASSECTD1 S Pixel Beginning column for trailing bias section of amp 2
BIASSECTD2 S Pixel Ending column for trailing bias section of amp 2
VX1 S Pixel X coordinate of 1st parallel virtual overscan origin
VY1 S Pixel Y coordinate of 1st parallel virtual overscan origin
VX2 S Pixel X coordinate of 1st parallel virtual overscan final corner
VY2 S Pixel Y coordinate of 1st parallel virtual overscan final corner
VX3 S Pixel X coordinate of 2nd parallel virtual overscan origin
VY3 S Pixel Y coordinate of 2nd parallel virtual overscan origin
VX4 S Pixel X coordinate of 2nd parallel virtual overscan final corner
VY4 S Pixel Y coordinate of 2nd parallel virtual overscan final corner
PEDIGREE CH*67 Pedigree of this row
DESCRIP CH*67 Source and quality of specified overscan regions

Selection Criteria: The OSC table is selected by DETECTOR. Table rows are selected by CCDAMP, CCDCHIP, BINX, and BINY.

Restrictions: None.

Required Additional Keywords:

FILETYPE = 'OVERSCAN'

11.3.5 Cosmic-Ray Rejection Parameter Table (CRR): <unique name>_crr.fits

Description: This reference table 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 and removed. 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, that pixel will be marked in the input image DQ array, if CRMASK is set to yes. Pixels with DQ values equal to BADINPDQ will be ignored in the cosmic ray search.

Format: The columns contained in the CRR table are listed in Table 11-11.

Table 11-11. Cosmic Ray Rejection Parameter Table (CRR), <uniquename>_crr.fits

Column Name Data Type Units Description
CRSPLIT S Number of exposures into which observation was split
MEANEXP R Sec Average exposure time for each image
SCALENSE CH*8 Scale factor applied to noise
INITGUES CH*8 Initial value estimate scheme (median, minimum)
SKYSUB CH*4 Sky subtraction scheme (none, mode)
CRSIGMAS CH*20 Rejection levels in each iteration
CRRADIUS R Pixel CR expansion radius
CRTHRESH R Rejection propagation threshold
BADINPDQ S Data quality flag bits used to reject input pixels
CRMASK B Flag CR-rejected pixels in input files?
CCDCHIP S CHIP to which these data apply
IRRAMP S ‘yes’ for IR row, ‘no’ for UVIS (in IR CRR table only)

Selection Criteria: The CRR table is selected by DETECTOR, USEAFTER, and in the IR table, IRRAMP. Rows within the table are selected by CRSPLIT and MEANEXP. The exposure time for each CR-SPLIT image is compared to the MEANEXP values in this table. The row containing the lowest MEANEXP that is still greater than the input image’s exposure time is selected. In practice, MEANEXP is always set to INDEF and there is only one row for each CHIP and CR-SPLIT value. For the IR table, the CR-SPLIT column is treated as listing the number of non-destructive readouts in the observation. Therefore, the table contains one row for each CR-SPLIT value from 2 through 16.

Restrictions: None.

Required Additional Keywords:

FILETYPE = 'COSMIC RAY REJECTION'

11.3.6 Image Distortion Coefficients Table (IDC) : <unique name>_idc.fits

Description: This reference table contains a description of the geometric distortion models for the WFC3 UVIS and IR detectors. A detailed description of the contents and usage of the IDCTAB with HST instruments is found in ISR ACS 2001-008 (Hack & Cox 2001). Briefly, the IDCTAB contains the coefficients of a polynomial fit that is used to transform image coordinates from raw (distorted) space to an undistorted space. It is utilized by calwf3 to geometrically transform calibrated images from raw detector space to an undistorted space.

Format: The IDCTAB contains the columns of data listed in Table 11-12. The table contains one row for each part of the detector that has its own distortion correction, as necessary. The primary header keyword NORDER is used to indicate the order of the polynomial that is represented in the table and the corresponding number of coefficients.

Table 11-12. Image Distortion Coefficients Table (IDC), <unique name>_idc.fits

Column Name Data Type Units Description
DETCHIP S ID of chip/detector used for observation
DIRECTION S Application direction (1=Forward, -1=Inverse)
FILTER S Filter to which the correction applies
XSIZE I pixels Raw image size in X direction
YSIZE I pixels Raw image size in Y direction
XREF R pixel X position of reference point
YREF R pixel Y position of reference point
THETA R degrees Angle between calibrated and uncalibrated Y axes
SCALE R arcsec Scale of square corrected pixel
V2REF R arcsec V2 position of reference point
V3REF R arcsec V3 position of reference point
CX10,CX11,... R Distortion coefficients for X position
CY10,CY11,... R Distortion coefficients for Y position

Selection Criteria: The IDC table is selected by DETECTOR. Rows are selected by DETCHIP.

Restrictions: None.

Required Additional Keywords:

FILETYPE = 'DISTORTION COEFFICIENTS'
NORDER = [n]             / Order of the polynomial fit
PARITY = 1, -1           / (x,y) to (V2,V3) conversion parity

11.3.7 AstroDrizzle Parameters Table (MDZ) : <unique name>_mdz.fits

Description: This table contains input parameters for AstroDrizzle, optimized for the widest range of science cases. These serve as default parameters for the instrument calibration pipeline to process any given single image or association. Observers should inspect these values and determine whether any adjustments or fine-tuning may be necessary for their science data.

See: .. _DrizzlePac Handbook http://documents.stsci.edu/hst/HST_overview/documents/DrizzlePac/ch44.html for more information.

Table 11-13. Astrodrizzle Parameter File (MDZ), <unique name>_mdz.fits

Column Name Data Type Units
FILTER S
NUMIMAGES I
MDRIZTAB B
REFIMAGE S
RUNFILE S
COEFFS S
CONTEXT B
CLEAN B
GROUP S
RA R Degrees
DEC R Degrees
BUILD B
GAIN S
GNKEYWORD S
READNOISE S
RNKEYWORD S
EXPTIME R Seconds
EXPKEYWORD S
CRBITVAL I
SHIFTFILE S
STATIC B
STATICFILE S
STATIC SIG R
SUBSKY B
SKYWIDTH R
SKYSTAT S
SKYLOWER R Electrons
SKYUPPER R Electrons
SKYCLIP I
SKYLSIGMA R
SKYUSIGMA R
DRIZ SEPARATE B
DRIZ SEP OUTNX I Pixels
DRIZ SEP OUTNY I Pixels
DRIZ SEP KERNEL S
DRIZ SEP SCALE R
DRIZ SEP PIXFRAC R
DRIZ SEP ROT R Degrees
DRIZ SEP FILLVAL R
DRIZ SEP BITS I
MEDIAN B
MEDIAN NEWMASKS B
COMBINE TYPE S
COMBINE NSIGMA I
COMBINE NLOW I
COMBINE NHIGH I
COMBINE LTHRESH R
COMBINE HTHRESH R
COMBINE GROW I Pixels
BLOT B
DRIZ CR B
DRIZ CR CORR B
DRIZ CR SN R
DRIZ CR SCALE R
DRIZ COMBINE B
FINAL OUTNX I Pixels
FINAL OUTNY I Pixels
FINAL KERNEL S
FINAL SCALE R Arcseconds
FINAL PIXFRAC R
FINAL ROT R Degrees
FINAL FILLVAL R
FINAL BITS I
BLOT INTERP S
BLOT SINSCL R Pixels

Selection Criteria: The Astrodrizzle Parameters File is selected by DETECTOR.

Restrictions: The value of the DRIZCORR keyword must not be OMIT.

Required Additional Keywords:

FILETYPE = 'MULTIDRIZZLE PARAMETERS'

11.3.8 Image Photometry Table (IMP) : <unique name>_imp.fits

Description: This reference table is used in the PHOTCORR step of the HSTCAL (IRAF-indepndent) version of the calwf3 pipeline (calwf3 version 3.0). The file, one for the IR channel and one for UVIS, contains the PHOTFLAM values for all configurations of that channel in the WFC3 instrument. PHOTFLAM is a keyword present in the main header of HST data. The value of this keyword for a particular instrument configuration is a measure of the inverse sensitivity (ergs/cm2/Ang/electron) for that configuration, and can be used to translate data from units of electrons to calibrated fluxes. In previous versions of the calwf3 pipeline, the PHOTFLAM value was calculated on the fly via a call to synphot. In the new HSTCAL version of the pipeline, this call to synphot has been replaced with the IMPHTTAB, which functions as a look-up table. For more details on the PHOTFLAM header keyword, see the WFC3 Data Handbook.

Table 11-14. Image Photometry File (IMP), <unique name>_imp.fits

Extension | Extension Name | Column Names
0 | Primary Header |
1 PHOTFLAM OBSMODE, DATACOL, PHOTFLAM, PEDIGREE, DESCRIP
2 PHOTPLAM OBSMODE, DATACOL, PHOTPLAM, PEDIGREE, DESCRIP
3 PHOTBW OBSMODE, DATACOL, PHOTBW, PEDIGREE, DESCRIP

Selection Criteria: The Image Photometry File is selected by DETECTOR.

Restrictions: The value of the PHOTCORR keyword cannot be OMIT.

Required Additional Keywords:

FILETYPE = 'IMAGE PHOTOMETRY TABLE'

11.4 WFC3 FITS File Headers

WFC3 FITS science file headers are given in the following subsections: one for the UVIS detector and one for the IR detector.

11.4.1 WFC3 UVIS Image Header

IMPLE  =                 T / data conform to FITS standard                   L1
   ITPIX  =             16 / bits per data value                             I2
   AXIS   =              0 / number of data axes                             I2
   XTEND  =              T / File may contain standard extensions            L1
   EXTEND =                / Number of standard extensions                   I2
   ROUPS  =              F / image is in group format                        L1
   ATE    =                / date this file was written (yyyy-mm-dd)         C10
   ILENAME=                / name of file                                    C26
   ILETYPE=                / type of data found in data file                 C09
   ELESCOP= HST            / telescope used to acquire data                  C03
   NSTRUME= WFC3           / identifier for instrument used to acquire data  C06
   QUINOX =         2000.0 / equinox of celestial coord. system              R4

           / DATA DESCRIPTION KEYWORDS

   OOTNAME=                / rootname of the observation set                 C21
   MAGETYP=                / type of exposure identifier                     C18
   RIMESI =                / instrument designated as prime                  C06

           / TARGET INFORMATION

   ARGNAME=                / proposer's target name                          C30
   A_TARG =                / right ascension of the target (deg) (J2000)     R8
   EC_TARG=                / declination of the target (deg) (J2000)         R8

           / PROPOSAL INFORMATION

   ROPOSID=                / PEP proposal identifier                         I4

   INENUM =                / proposal logsheet line number                   C15
   R_INV_L=                / last name of principal investigator             C30
   R_INV_F=                / first name of principal investigator            C20
   R_INV_M=                / middle name / initial of principal investigator C20

           / EXPOSURE INFORMATION

   UNANGLE=                / angle between sun and V1 axis                   R4
   OONANGL=                / angle between moon and V1 axis                  R4
   UN_ALT =                / altitude of the sun above Earth's limb          R4
   GSLOCK = FINE           / commanded FGS lock (FINE,COARSE,GYROS,UNKNOWN)  C07
   ATE-OBS=                / UT date of start of observation (yyyy-mm-dd)    C10
   IME-OBS=                / UT time of start of observation (hh:mm:ss)      C08
   XPSTART=                / exposure start time (Modified Julian Date)      R8
   XPEND  =                / exposure end time (Modified Julian Date)        R8
   XPTIME =                / exposure duration (seconds)--calculated         R4
   XPFLAG = NORMAL         / Exposure interruption indicator                 C13

           / POINTING INFORMATION

   A_V3   =                / position angle of V3-axis of HST (deg)          R4

           / TARGET OFFSETS (POSTARGS)

   OSTARG1=                / POSTARG in axis 1 direction                     R4
   OSTARG2=                / POSTARG in axis 2 direction                     R4

           / DIAGNOSTIC KEYWORDS

   AL_VER =                / CALWF3 code version                             C24
   ROCTIME=                / Pipeline processing time (MJD)                  R8

           / SCIENCE INSTRUMENT CONFIGURATION

   BSTYPE =                / observation type - imaging or spectroscopic     C14
   BSMODE =                / operating mode                                  C08
   TEIMAGE=                / type of Charge Transfer Image, if applicable    C04
   CLAMP  =                / lamp status, NONE or name of lamp which is on   C09
   UBARRAY=                / data from a subarray (T) or full frame (F)      L1
   ETECTOR=                / detector in use: UVIS or IR                     C04
   ILTER  =                / element selected from filter wheel              C18
   PERTURE=                / aperture name                                   C16
   ROPAPER=                / proposed aperture name                          C16
   IRIMAGE= NONE           / direct image for grism or prism exposure        C09
   TEDIR  = NONE           / CTE measurement direction: serial or parallel   C08
   RSPLIT =                / number of cosmic ray split exposures            I2

           / CALIBRATION SWITCHES: PERFORM, OMIT, COMPLETE

   RTERR  =              T / write out error array extension                 L1
   QICORR =                / data quality initialization                     C08
   TODCORR=                / correct for A to D conversion errors            C08
   LEVCORR=                / subtract bias level computed from overscan      C08
   IASCORR=                / Subtract bias image                             C08
   LSHCORR=                / post flash correction                           C08
   RCORR  =                / combine observations to reject cosmic rays      C08
   XPSCORR=                / process individual observations after cr-reject C08
   HADCORR=                / apply shutter shading correction                C08
   ARKCORR=                / Subtract dark image                             C08
   LATCORR=                / flat field data                                 C08
   HOTCORR=                / populate photometric header keywords            C08
   RIZCORR=                / drizzle processing                              C08

           / CALIBRATION REFERENCE FILES

   PIXTAB =                / bad pixel table                                 C23
   CDTAB  =                / detector calibration parameters                 C23
   TODTAB =                / analog to digital correction file               C23
   SCNTAB =                / detector overscan table                         C23
   IASFILE=                / bias image file name                            C23
   LSHFILE=                / post flash correction file name                 C23
   RREJTAB=                / cosmic ray rejection parameters                 C23
   HADFILE=                / shutter shading correction file                 C23
   ARKFILE=                / dark image file name                            C23
   FLTFILE=                / pixel to pixel flat field file name             C23
   FLTFILE=                / delta flat field file name                      C23
   FLTFILE=                / low order flat                                  C23
   RAPHTAB=                / the HST graph table                             C23
   OMPTAB =                / the HST components table                        C23
   DCTAB  =                / image distortion correction table               C23

           / COSMIC RAY REJECTION ALGORITHM PARAMETERS

   EANEXP =                / reference exposure time for parameters          R4
   CALENSE=                / multiplicative scale factor applied to noise    R4
   NITGUES=                / initial guess method (MIN or MED)               C03
   KYSUB  =                / sky value subtracted (MODE or NONE)             C04
   KYSUM  =                / sky level from the sum of all constituent imagesR4
   RSIGMAS=                / statistical rejection criteria                  C15
   RRADIUS=                / rejection propagation radius (pixels)           R4
   RTHRESH=                / rejection propagation threshold                 R4
   ADINPDQ=                / data quality flag bits to reject                I2
   EJ_RATE=                / rate at which pixels are affected by cosmic raysR4
   RMASK  =                / flag CR-rejected pixels in input files (T/F)    L1

           / PATTERN KEYWORDS

   ATTERN1= NONE           / primary pattern type                            C24
   1_SHAPE=                / primary pattern shape                           C18
   1_PURPS=                / primary pattern purpose                         C10
   1_NPTS =                / number of points in primary pattern             I2
   1_PSPAC=                / point spacing for primary pattern (arc-sec)     R4
   1_LSPAC=                / line spacing for primary pattern (arc-sec)      R4
   1_ANGLE=                / angle between sides of parallelogram patt (deg) R4
   1_FRAME=                / coordinate frame of primary pattern             C09
   1_ORINT=                / orientation of pattern to coordinate frame (deg)R4
   1_CENTR=                / center pattern relative to pointing (yes/no)    C03
   ATTSTEP=                / position number of this point in the pattern    I2

           / POST FLASH PARAMETERS

   LASHDUR=                / Exposure time in seconds: 0.1 to 409.5          R4
   LASHCUR=                / Post flash current: OFF, LOW, MED, HIGH         C04
   LASHSTA=                / Status: SUCCESSFUL, ABORTED, NOT PERFORMED      C16
   HUTRPOS=                / Shutter position: A or B                        C05

           / ENGINEERING PARAMETERS

   CDAMP  =                / CCD Amplifier Readout Configuration             C04
   CDGAIN =                / commanded gain of CCD                           I2
   CDOFSTA=                / commanded CCD bias offset for amplifier A       I4
   CDOFSTB=                / commanded CCD bias offset for amplifier B       I4
   CDOFSTC=                / commanded CCD bias offset for amplifier C       I4
   CDOFSTD=                / commanded CCD bias offset for amplifier D       I4

           / CALIBRATED ENGINEERING PARAMETERS

   TODGNA =                / calibrated gain for amplifier A                 R4
   TODGNB =                / calibrated gain for amplifier B                 R4
   TODGNC =                / calibrated gain for amplifier C                 R4
   TODGND =                / calibrated gain for amplifier D                 R4
   EADNSEA=                / calibrated read noise for amplifier A           R4
   EADNSEB=                / calibrated read noise for amplifier B           R4
   EADNSEC=                / calibrated read noise for amplifier C           R4
   EADNSED=                / calibrated read noise for amplifier D           R4

           / ASSOCIATION KEYWORDS

   SN_ID  = NONE           / unique identifier assigned to association       C10
   SN_TAB = NONE           / name of the association table                   C23
   SN_MTYP=                / Role of the Exposure in the Association         C12

   END

   TENSION= IMAGE          / extension type                                  C08
   ITPIX  =            -32 / bits per data value                             I2
   AXIS   =              2 / number of data axes                             I2
   AXIS1  =                / length of first data axis                       I4
   AXIS2  =                / length of second data axis                      I4
   COUNT  =              0 / number of group parameters                      I2
   COUNT  =              1 / number of groups                                I2
   NHERIT =              T / inherit the primary header                      L1
   XTNAME = SCI            / extension name                                  C06
   XTVER  =                / extension version number                        I2
   OOTNAME=                / rootname of the observation set                 C21
   XPNAME =                / 9 character exposure identifier                 C09
   ATAMIN =                / the minimum value of the data                   R8
   ATAMAX =                / the maximum value of the data                   R8
   UNIT   =                / brightness units                                C18
   SCALE  =            1.0 / scale factor for array value to physical value  R8
   ZERO   =         32768. / physical value for an array value of zero       R8

           / WFC CCD CHIP IDENTIFICATION

   CDCHIP =                / CCD chip (1 or 2)                               I2

           / World Coordinate System and Related Parameters

   RPIX1  =                / x-coordinate of reference pixel                 R8
   RPIX2  =                / y-coordinate of reference pixel                 R8
   RVAL1  =                / first axis value at reference pixel             R8
   RVAL2  =                / second axis value at reference pixel            R8
   TYPE1  = RA---TAN       / the coordinate type for the first axis          C08
   TYPE2  = DEC--TAN       / the coordinate type for the second axis         C08
   D1_1   =            1.0 / partial of first axis coordinate w.r.t. x       R8
   D1_2   =            0.0 / partial of first axis coordinate w.r.t. y       R8
   D2_1   =            0.0 / partial of second axis coordinate w.r.t. x      R8
   D2_2   =            1.0 / partial of second axis coordinate w.r.t. y      R8
   TV1    =              0 / offset in X to subsection start                 R4
   TV2    =              0 / offset in Y to subsection start                 R4
   TM1_1  =              1 / reciprocal of sampling rate in X                R4
   TM2_2  =              1 / reciprocal of sampling rate in Y                R4
   RIENTAT=                / position angle of image y axis (deg. e of n)    R4
   A_APER =                / Position Angle of reference aperture center     R8

           / READOUT DEFINITION PARAMETERS

   ENTERA1=                / subarray axis1 center pt in unbinned dect. pix  I4
   ENTERA2=                / subarray axis2 center pt in unbinned dect. pix  I4
   IZAXIS1=                / subarray axis1 size in unbinned detector pixels I4
   IZAXIS2=                / subarray axis2 size in unbinned detector pixels I4
   INAXIS1=              1 / axis1 data bin size in unbinned detector pixels I2
   INAXIS2=              1 / axis2 data bin size in unbinned detector pixels I2

           / PHOTOMETRY KEYWORDS

   HOTMODE=                / observation configuration for photometric calib C50
   HOTFLAM=                / inverse sensitivity, ergs/cm2/Ang/electron      R8
   HOTFNU =                / inverse sensitivity, Jy*sec/electron            R8
   HOTZPT =                / ST magnitude zero point                         R4
   HOTPLAM=                / Pivot wavelength (Angstroms)                    R4
   HOTBW  =                / RMS bandwidth of filter plus detector           R4

           / REPEATED EXPOSURES INFO

   COMBINE=              1 / number of images combined during CR rejection   I2

           / DATA PACKET INFORMATION

   ILLCNT =              0 / number of segments containing fill              I4
   RRCNT  =              0 / number of segments containing errors            I4
   ODPSFF =              F / podps fill present (T/F)                        L1
   TDCFFF =              F / ST DDF fill present (T/F)                       L1
   TDCFFP = x5569          / ST DDF fill pattern (hex)                       C06

           / IMAGE STATISTICS AND DATA QUALITY FLAGS

   GOODPIX=                / number of good pixels                           I4
   DQFLAGS=          31743 / serious data quality flags                      I4
   OODMIN =                / minimum value of good pixels                    R4
   OODMAX =                / maximum value of good pixels                    R4
   OODMEAN=                / mean value of good pixels                       R4
   NRMIN  =                / minimum signal to noise of good pixels          R4
   NRMAX  =                / maximum signal to noise of good pixels          R4
   NRMEAN =                / mean value of signal to noise of good pixels    R4
   OFTERRS=                / number of soft error pixels (DQF=1)             I4
   EANDARK=                / average of the dark values subtracted           R4
   EANBLEV=                / average of all bias levels subtracted           R4
   EANFLSH=                / Mean number of counts in post flash exposure    R4

   END

   XTENSION= IMAGE          / extension type                                  C08
   BITPIX  =            -32 / 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
   INHERIT =              T / inherit the primary header                      L1
   EXTNAME = ERR            / extension name                                  C06
   EXTVER  =                / extension version number                        I2
   ROOTNAME=                / rootname of the observation set                 C21
   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

   CRPIX1  =                / x-coordinate of reference pixel                 R8
   CRPIX2  =                / y-coordinate of reference pixel                 R8
   CRVAL1  =                / first axis value at reference pixel             R8
   CRVAL2  =                / second axis value at reference pixel            R8
   CTYPE1  = RA---TAN       / the coordinate type for the first axis          C08
   CTYPE2  = DEC--TAN       / the coordinate type for the second axis         C08
   CD1_1   =            1.0 / partial of first axis coordinate w.r.t. x       R8
   CD1_2   =            0.0 / partial of first axis coordinate w.r.t. y       R8
   CD2_1   =            0.0 / partial of second axis coordinate w.r.t. x      R8
   CD2_2   =            1.0 / partial of second axis coordinate w.r.t. y      R8
   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
   ORIENTAT=                / position angle of image y axis (deg. e of n)    R4
   PA_APER =                / Position Angle of reference aperture center     R8

            / IMAGE STATISTICS AND DATA QUALITY FLAGS

   NGOODPIX=                / number of good pixels                           I4
   SDQFLAGS=          31743 / serious data quality flags                      I4
   GOODMIN =                / minimum value of good pixels                    R4
   GOODMAX =                / maximum value of good pixels                    R4
   GOODMEAN=                / mean value of good pixels                       R4

   END

   XTENSION= IMAGE          / extension type                                  C08
   BITPIX  =             16 / 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
   INHERIT =              T / inherit the primary header                      L1
   EXTNAME = DQ             / extension name                                  C06
   EXTVER  =                / extension version number                        I2
   ROOTNAME=                / rootname of the observation set                 C21
   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

   CRPIX1  =                / x-coordinate of reference pixel                 R8
   CRPIX2  =                / y-coordinate of reference pixel                 R8
   CRVAL1  =                / first axis value at reference pixel             R8
   CRVAL2  =                / second axis value at reference pixel            R8
   CTYPE1  = RA---TAN       / the coordinate type for the first axis          C08
   CTYPE2  = DEC--TAN       / the coordinate type for the second axis         C08
   CD1_1   =            1.0 / partial of first axis coordinate w.r.t. x       R8
   CD1_2   =            0.0 / partial of first axis coordinate w.r.t. y       R8
   CD2_1   =            0.0 / partial of second axis coordinate w.r.t. x      R8
   CD2_2   =            1.0 / partial of second axis coordinate w.r.t. y      R8
   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
   ORIENTAT=                / position angle of image y axis (deg. e of n)    R4
   PA_APER =                / Position Angle of reference aperture center     R8

   END

11.4.2 WFC3 IR Image Header

SIMPLE  =              T / data conform to FITS standard                   L1
BITPIX  =             16 / 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                                    C26
FILETYPE=                / type of data found in data file                 C09
TELESCOP= HST            / telescope used to acquire data                  C03
INSTRUME= WFC3           / identifier for instrument used to acquire data  C06
EQUINOX =         2000.0 / equinox of celestial coord. system              R4

         / DATA DESCRIPTION KEYWORDS

ROOTNAME=                / rootname of the observation set                 C21
IMAGETYP=                / type of exposure identifier                     C18
PRIMESI =                / instrument designated as prime                  C06

         / TARGET INFORMATION

TARGNAME=                / proposer's target name                          C30
RA_TARG =                / right ascension of the target (deg) (J2000)     R8
DEC_TARG=                / declination of the target (deg) (J2000)         R8

         / PROPOSAL INFORMATION

PROPOSID=                / PEP proposal identifier                         I4
LINENUM =                / proposal logsheet line number                   C15
PR_INV_L=                / last name of principal investigator             C30
PR_INV_F=                / first name of principal investigator            C20
PR_INV_M=                / middle name / initial of principal investigator C20

         / EXPOSURE INFORMATION

SUNANGLE=                / angle between sun and V1 axis                   R4
MOONANGL=                / angle between moon and V1 axis                  R4
SUN_ALT =                / altitude of the sun above Earth's limb          R4
FGSLOCK = FINE           / commanded FGS lock (FINE,COARSE,GYROS,UNKNOWN)  C07
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

         / POINTING INFORMATION

PA_V3   =                / position angle of V3-axis of HST (deg)          R4

         / TARGET OFFSETS (POSTARGS)

POSTARG1=                / POSTARG in axis 1 direction                     R4
POSTARG2=                / POSTARG in axis 2 direction                     R4

         / DIAGNOSTIC KEYWORDS

CAL_VER =                / CALWF3 code version                             C24
PROCTIME=                / Pipeline processing time (MJD)                  R8

         / 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= IR             / detector in use: UVIS or IR                     C04
FILTER  =                / element selected from filter wheel              C18
SAMP_SEQ=                / MULTIACCUM exposure time sequence name          C08
NSAMP   =                / number of MULTIACCUM samples                    I2
SAMPZERO=                / sample time of the zeroth read (sec)            R4
APERTURE=                / aperture name                                   C16
PROPAPER=                / proposed aperture name                          C16
DIRIMAGE= NONE           / direct image for grism or prism exposure        C09

         / PHOTOMETRY KEYWORDS

PHOTMODE=                / observation configuration for photometric calib C50
PHOTFLAM=                / inverse sensitivity, ergs/cm2/Ang/electron      R8
PHOTFNU =                / inverse sensitivity, Jy*sec/electron            R8
PHOTZPT =                / ST magnitude zero point                         R4
PHOTPLAM=                / Pivot wavelength                                R4
PHOTBW  =                / RMS bandwidth of filter plus detector           R4

         / POST-SAA DARK KEYWORDS

SAA_EXIT=                / time of last exit from SAA contour level 23     C17
SAA_TIME=                / seconds since last exit from SAA contour level 2I4
SAA_DARK= N/A            / association name for post-SAA dark exposures    C09
SAACRMAP= N/A            / SAA cosmic ray map file                         C18

         / CALIBRATION SWITCHES: PERFORM, OMIT, COMPLETE

DQICORR =                / data quality initialization                     C08
ZSIGCORR=                / zero read signal correction                     C08
ZOFFCORR=                / subtract MULTIACCUM zero read                   C08
DARKCORR=                / Subtract dark image                             C08
BLEVCORR=                / subtract bias computed from reference pixels    C08
NLINCORR=                / correct for detector nonlinearities             C08
CRCORR  =                / identify cosmic ray hits                        C08
FLATCORR=                / flat field data                                 C08
UNITCORR=                / convert to count rates                          C08
PHOTCORR=                / populate photometric header keywords            C08
RPTCORR =                / add individual repeat observations              C08
DRIZCORR=                / drizzle processing                              C08

         / CALIBRATION REFERENCE FILES

BPIXTAB =                / bad pixel table                                 C23
CCDTAB  =                / detector calibration parameters                 C23
OSCNTAB =                / detector overscan table                         C23
CRREJTAB=                / cosmic ray rejection parameters                 C23
DARKFILE=                / dark image file name                            C23
NLINFILE=                / detector nonlinearities file                    C23
PFLTFILE=                / pixel to pixel flat field file name             C23
DFLTFILE=                / delta flat field file name                      C23
LFLTFILE=                / low order flat field file name                  C23
GRAPHTAB=                / the HST graph table                             C23
COMPTAB =                / the HST components table                        C23
IDCTAB  =                / image distortion correction table               C23

         / COSMIC RAY REJECTION ALGORITHM PARAMETERS

MEANEXP =                / reference exposure time for parameters          R4
SCALENSE=                / multiplicative scale factor applied to noise    R4
INITGUES=                / initial guess method (MIN or MED)               C03
SKYSUB  =                / sky value subtracted (MODE or NONE)             C04
SKYSUM  =                / sky level from the sum of all constituent imagesR4
CRSIGMAS=                / statistical rejection criteria                  C15
CRRADIUS=                / rejection propagation radius (pixels)           R4
CRTHRESH=                / rejection propagation threshold                 R4
BADINPDQ=                / data quality flag bits to reject                I2
REJ_RATE=                / rate at which pixels are affected by cosmic raysR4
CRMASK  =                / flag CR-rejected pixels in input files (T/F)    L1

         / PATTERN KEYWORDS

PATTERN1= NONE           / primary pattern type                            C24
P1_SHAPE=                / primary pattern shape                           C18
P1_PURPS=                / primary pattern purpose                         C10
P1_NPTS =                / number of points in primary pattern             I2
P1_PSPAC=                / point spacing for primary pattern (arc-sec)     R4
P1_LSPAC=                / line spacing for primary pattern (arc-sec)      R4
P1_ANGLE=                / angle between sides of parallelogram patt (deg) R4
P1_FRAME=                / coordinate frame of primary pattern             C09
P1_ORINT=                / orientation of pattern to coordinate frame (deg)R4
P1_CENTR=                / center pattern relative to pointing (yes/no)    C03
PATTSTEP=                / position number of this point in the pattern    I2

         / ENGINEERING PARAMETERS

CCDAMP  =                / CCD Amplifier Readout Configuration             C04
CCDGAIN =                / commanded gain of CCD                           I2
CCDOFSAB=                / commanded CCD bias offset for amps A&B          I4
CCDOFSCD=                / commanded CCD bias offset for amps C&D          I4

         / CALIBRATED ENGINEERING PARAMETERS

ATODGNA =                / calibrated gain for amplifier A                 R4
ATODGNB =                / calibrated gain for amplifier B                 R4
ATODGNC =                / calibrated gain for amplifier C                 R4
ATODGND =                / calibrated gain for 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

         / ASSOCIATION KEYWORDS

ASN_ID  = NONE           / unique identifier assigned to association       C10
ASN_TAB = NONE           / name of the association table                   C23
ASN_MTYP=                / Role of the Exposure in the Association         C12

END


XTENSION= IMAGE          / extension type                                  C08
BITPIX  =            -32 / 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
INHERIT =              T / inherit the primary header                      L1
EXTNAME = SCI            / extension name                                  C06
EXTVER  =                / extension version number                        I2
ROOTNAME=                / rootname of the observation set                 C21
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

         / World Coordinate System and Related Parameters

CRPIX1  =                / x-coordinate of reference pixel                 R8
CRPIX2  =                / y-coordinate of reference pixel                 R8
CRVAL1  =                / first axis value at reference pixel             R8
CRVAL2  =                / second axis value at reference pixel            R8
CTYPE1  = RA---TAN       / the coordinate type for the first axis          C08
CTYPE2  = DEC--TAN       / the coordinate type for the second axis         C08
CD1_1   =            1.0 / partial of first axis coordinate w.r.t. x       R8
CD1_2   =            0.0 / partial of first axis coordinate w.r.t. y       R8
CD2_1   =            0.0 / partial of second axis coordinate w.r.t. x      R8
CD2_2   =            1.0 / partial of second axis coordinate w.r.t. y      R8
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
ORIENTAT=                / position angle of image y axis (deg. e of n)    R4
PA_APER =                / Position Angle of reference aperture center     R8

         / READOUT DEFINITION PARAMETERS

CENTERA1=                / subarray axis1 center pt in unbinned dect. pix  I4
CENTERA2=                / subarray axis2 center pt in unbinned dect. pix  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

         / DATA PACKET INFORMATION

FILLCNT =              0 / number of segments containing fill              I4
ERRCNT  =              0 / number of segments containing errors            I4
PODPSFF =              F / podps fill present (T/F)                        L1
STDCFFF =              F / ST DDF fill present (T/F)                       L1
STDCFFP = x5569          / ST DDF fill pattern (hex)                       C06

         / READOUT PARAMETERS

SAMPNUM =                / MULTIACCUM sample number                        I2
SAMPTIME=                / total integration time (sec)                    R4
DELTATIM=                / integration time of this sample (sec)           R4
ROUTTIME=                / UT time of array readout (MJD)                  R8
TDFTRANS=                / number of TDF transitions during current sample I4

         / IMAGE STATISTICS AND DATA QUALITY FLAGS

NGOODPIX=                / number of good pixels                           I4
SDQFLAGS=          31743 / serious data quality flags                      I4
GOODMIN =                / minimum value of good pixels                    R4
GOODMAX =                / maximum value of good pixels                    R4
GOODMEAN=                / mean value of good pixels                       R4
SNRMIN  =                / minimum signal to noise of good pixels          R4
SNRMAX  =                / maximum signal to noise of good pixels          R4
SNRMEAN =                / mean value of signal to noise of good pixels    R4
SOFTERRS=                / number of soft error pixels (DQF=1)             I4
MEANDARK=                / average of the dark values subtracted           R4
MEANBLEV=                / average of all bias levels subtracted           R4

END

XTENSION= IMAGE          / extension type                                  C08
BITPIX  =            -32 / 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
INHERIT =              T / inherit the primary header                      L1
EXTNAME = ERR            / extension name                                  C06
EXTVER  =                / extension version number                        I2
ROOTNAME=                / rootname of the observation set                 C21
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

CRPIX1  =                / x-coordinate of reference pixel                 R8
CRPIX2  =                / y-coordinate of reference pixel                 R8
CRVAL1  =                / first axis value at reference pixel             R8
CRVAL2  =                / second axis value at reference pixel            R8
CTYPE1  = RA---TAN       / the coordinate type for the first axis          C08
CTYPE2  = DEC--TAN       / the coordinate type for the second axis         C08
CD1_1   =            1.0 / partial of first axis coordinate w.r.t. x       R8
CD1_2   =            0.0 / partial of first axis coordinate w.r.t. y       R8
CD2_1   =            0.0 / partial of second axis coordinate w.r.t. x      R8
CD2_2   =            1.0 / partial of second axis coordinate w.r.t. y      R8
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
ORIENTAT=                / position angle of image y axis (deg. e of n)    R4
PA_APER =                / Position Angle of reference aperture center     R8

         / IMAGE STATISTICS AND DATA QUALITY FLAGS

NGOODPIX=                / number of good pixels                           I4
SDQFLAGS=          31743 / serious data quality flags                      I4
GOODMIN =                / minimum value of good pixels                    R4
GOODMAX =                / maximum value of good pixels                    R4
GOODMEAN=                / mean value of good pixels                       R4

END

XTENSION= IMAGE          / extension type                                  C08
BITPIX  =             16 / 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
INHERIT =              T / inherit the primary header                      L1
EXTNAME = DQ             / extension name                                  C06
EXTVER  =                / extension version number                        I2
ROOTNAME=                / rootname of the observation set                 C21
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

CRPIX1  =                / x-coordinate of reference pixel                 R8
CRPIX2  =                / y-coordinate of reference pixel                 R8
CRVAL1  =                / first axis value at reference pixel             R8
CRVAL2  =                / second axis value at reference pixel            R8
CTYPE1  = RA---TAN       / the coordinate type for the first axis          C08
CTYPE2  = DEC--TAN       / the coordinate type for the second axis         C08
CD1_1   =            1.0 / partial of first axis coordinate w.r.t. x       R8
CD1_2   =            0.0 / partial of first axis coordinate w.r.t. y       R8
CD2_1   =            0.0 / partial of second axis coordinate w.r.t. x      R8
CD2_2   =            1.0 / partial of second axis coordinate w.r.t. y      R8
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
ORIENTAT=                / position angle of image y axis (deg. e of n)    R4
PA_APER =                / Position Angle of reference aperture center     R8

END

XTENSION= IMAGE          / extension type                                  C08
BITPIX  =             16 / 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
INHERIT =              T / inherit the primary header                      L1
EXTNAME = SAMP           / extension name                                  C06
EXTVER  =                / extension version number                        I2
ROOTNAME=                / rootname of the observation set                 C21
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

CRPIX1  =                / x-coordinate of reference pixel                 R8
CRPIX2  =                / y-coordinate of reference pixel                 R8
CRVAL1  =                / first axis value at reference pixel             R8
CRVAL2  =                / second axis value at reference pixel            R8
CTYPE1  = RA---TAN       / the coordinate type for the first axis          C08
CTYPE2  = DEC--TAN       / the coordinate type for the second axis         C08
CD1_1   =            1.0 / partial of first axis coordinate w.r.t. x       R8
CD1_2   =            0.0 / partial of first axis coordinate w.r.t. y       R8
CD2_1   =            0.0 / partial of second axis coordinate w.r.t. x      R8
CD2_2   =            1.0 / partial of second axis coordinate w.r.t. y      R8
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
ORIENTAT=                / position angle of image y axis (deg. e of n)    R4
PA_APER =                / Position Angle of reference aperture center     R8

END

XTENSION= IMAGE          / extension type                                  C08
BITPIX  =            -32 / 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
INHERIT =              T / inherit the primary header                      L1
EXTNAME = TIME           / extension name                                  C06
EXTVER  =                / extension version number                        I2
ROOTNAME=                / rootname of the observation set                 C21
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

CRPIX1  =                / x-coordinate of reference pixel                 R8
CRPIX2  =                / y-coordinate of reference pixel                 R8
CRVAL1  =                / first axis value at reference pixel             R8
CRVAL2  =                / second axis value at reference pixel            R8
CTYPE1  = RA---TAN       / the coordinate type for the first axis          C08
CTYPE2  = DEC--TAN       / the coordinate type for the second axis         C08
CD1_1   =            1.0 / partial of first axis coordinate w.r.t. x       R8
CD1_2   =            0.0 / partial of first axis coordinate w.r.t. y       R8
CD2_1   =            0.0 / partial of second axis coordinate w.r.t. x      R8
CD2_2   =            1.0 / partial of second axis coordinate w.r.t. y      R8
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
ORIENTAT=                / position angle of image y axis (deg. e of n)    R4
PA_APER =                / Position Angle of reference aperture center     R8

END

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