JP-3455: Fix bug in new MIRI imager photom correction (#8102)

spacetelescope · Dec 1, 2023 · c5a0371 · c5a0371
1 parent faee866
commit c5a0371
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Showing 4 changed files with 23 additions and 4 deletions.
diff --git a/CHANGES.rst b/CHANGES.rst
@@ -64,7 +64,8 @@ imprint
 photom
 --------
 
-- Added time-dependent correction for MIRI Imager data [#8096, spacetelescope/stdatamodels#235]
+- Added time-dependent correction for MIRI Imager data.
+  [#8096, #8102, spacetelescope/stdatamodels#235]
 
 pixel_replace
 -------------

diff --git a/docs/jwst/photom/main.rst b/docs/jwst/photom/main.rst
@@ -76,6 +76,14 @@ The step also computes the equivalent conversion factor to units of
 microJy/square-arcsecond (or microjanskys) and stores it in the header
 keyword PHOTUJA2.
 
+MIRI Imaging
+^^^^^^^^^^^^
+For MIRI imaging mode, the reference file can optionally contain a table of
+coefficients that are used to apply time-dependent corrections to the scalar
+conversion factor. If the time-dependent coefficients are present in the
+reference file, the photom step will apply the correction based on the
+observation date of the exposure being processed.
+
 NIRSpec Fixed-Slit Primary Slit
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 The primary slit in a NIRSpec fixed-slit exposure receives special handling.

diff --git a/docs/jwst/references_general/photom_reffile.inc b/docs/jwst/references_general/photom_reffile.inc
@@ -60,6 +60,16 @@ instrument modes, as shown in the tables below.
 |            |       | uncertainty    | float     | scalar     | MJy/steradian/(DN/sec) |
 +------------+-------+----------------+-----------+------------+------------------------+
 
+The MIRI Imager PHOTOM reference file can contain an optional BINTABLE extension
+named "TIMECOEFF", containing coefficients for an time-dependent correction. The format
+of this additional table extension is as follows:
+
+==========  ========  =====  ===========  =========  
+EXTNAME     XTENSION  NAXIS  Dimensions   Data type
+==========  ========  =====  ===========  =========
+TIMECOEFF   BINTABLE    2    TFIELDS = 3  float32
+==========  ========  =====  ===========  =========
+
 :Data model: `~jwst.datamodels.MirLrsPhotomModel`
 
 +------------+-------+----------------+-----------+------------+------------------------+

diff --git a/jwst/photom/photom.py b/jwst/photom/photom.py
@@ -463,15 +463,15 @@ def calc_miri(self, ftab):
                 warnings.simplefilter("ignore")
                 row = find_row(ftab.phot_table, fields_to_match)
             if row is None:
-
+                # Search again using subarray="GENERIC" for old ref files
                 fields_to_match = {'subarray': 'GENERIC',
                                    'filter': self.filter}
                 row = find_row(ftab.phot_table, fields_to_match)
                 if row is None:
                     return
-                self.photom_io(ftab.phot_table[row])
 
-            # Check if reference file contains the coefficients for the time-dependent correction of the PHOTOM value
+            # Check to see if the reference file contains the coefficients for the
+            # time-dependent correction of the PHOTOM value
             try:
                 ftab.getarray_noinit("timecoeff")
                 log.info("Applying the time-dependent correction to the PHOTOM value.")