Documentation updates for NIRSpec MOS/FS

docs/jwst/exp_to_source/main.rst

@@ -34,14 +34,21 @@ configuration of MSA slitlets with a source assigned to each slitlet.
 The source-to-slitlet linkage is carried along in the information contained
 in the MSA metadata file used during :ref:`calwebb_spec2 <calwebb_spec2>`
 processing. Each slitlet instance created by the :ref:`extract_2d <extract_2d_step>`
-step stores the source ID (a simple integer number) in the SOURCEID keyword of
+step stores the source name in the SRCNAME keyword of
 the SCI extension header for the slitlet. The ``exp_to_source`` tool uses
-the SOURCEID values to sort the data from each input product into an
+the SRCNAME values to sort the data from each input product into an
 appropriate source-based output product.
 
-NIRSpec Fixed-Slit
+If fixed slit targets are planned as part of a NIRSpec MOS exposure, they
+will also have sources identified by the MSA metadata file.  The associated
+SRCNAME values are used to sort the data from these slits in the same way the
+MSA slitlets are sorted.  In this combined mode, the products containing
+MOS slitlets are marked with EXP_TYPE = "NRS_MSASPEC" after sorting; the models
+containing fixed slits are marked with EXP_TYPE = "NRS_FIXEDSLIT".
+
+NIRSpec Fixed Slit
 ^^^^^^^^^^^^^^^^^^
-NIRSpec fixed-slit observations do not have sources identified with each
+NIRSpec fixed slit observations do not have sources identified with each
 slit, so the slit names, e.g. S200A1, S1600A1, etc., are mapped to predefined
 source ID values, as follows:
 

docs/jwst/flatfield/main.rst

@@ -104,7 +104,7 @@ is applied to the slit data, but that correction is not appropriate for the
 background signal contained in the slit, and hence corrections must be
 applied later in the :ref:`master background <master_background_step>` step.
 
-So in this case the `flatfield` step will compute 2D arrays of conversion
+In this case, the `flatfield` step will compute 2D arrays of conversion
 factors that are appropriate for a uniform source and for a point source,
 and store those correction factors in the "FLATFIELD_UN" and "FLATFIELD_PS"
 extensions, respectively, of the output data product. The point source
@@ -118,7 +118,7 @@ wavelength-dependent. A uniform source does not require wavelength corrections
 and hence the flatfield conversions will differ for point and uniform
 sources. Any secondary slits that may be included in a fixed slit exposure
 do not have source centering information available, so the
-:ref:`wavecorr <wavecorr_step>` step is not applied, and hence there's no
+:ref:`wavecorr <wavecorr_step>` step is not applied, and there is no
 difference between the point source and uniform source flatfield
 conversions for those slits.
 

docs/jwst/master_background/description.rst

@@ -295,9 +295,9 @@ source centering within the slit, hence slits containing uniform sources receive
 the same flat-field and photometric calibrations as background spectra and
 therefore don't require corrections for those two calibrations. Furthermore, the
 source position in the slit is only known for the primary slit in an exposure, so
-secondary slits are always handled as extended sources, and no wavelength correction is
-applied, and therefore again the flat-field and photometric calibrations are
-the same as for background spectra.
+secondary slits are always handled as extended sources, no wavelength correction is
+applied, and therefore again the flat-field, photometric, and pathloss calibrations
+are the same as for background spectra.
 
 Fixed slits planned as part of a combined MOS and FS observation are an
 exception to this rule.  These targets may each be identified as
@@ -306,7 +306,7 @@ point sources, with location information for each given in the
 this way are treated in the same manner as the primary fixed slit in standard
 FS observations.
 
-Therefore if a fixed slit contains a point source (as given by the SRCTYPE keyword)
+Therefore, if a fixed slit contains a point source (as given by the SRCTYPE keyword)
 the corrections that need to be applied to the 2-D master background for that slit are:
 
 .. math::

docs/jwst/nsclean/main.rst

@@ -103,6 +103,10 @@ processing MOS and IFU images. The masked region is currently hardwired
 in the step to image indexes [1:2048, 923:1116], where the indexes are
 in x, y order and in 1-indexed values.
 
+Note, however, that it is possible to plan one or more fixed slit targets
+alongside MSA slitlets in MOS observations. In this situation, the fixed
+slit region is not automatically masked.
+
 Left/Right Reference Pixel Columns
 ----------------------------------
 Full-frame images contain 4 columns of reference pixels on the left and

docs/jwst/photom/main.rst

@@ -84,9 +84,9 @@ 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
+NIRSpec Fixed Slit Primary Slit
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-The primary slit in a NIRSpec fixed-slit exposure receives special handling.
+The primary slit in a NIRSpec fixed slit exposure receives special handling.
 If the primary slit, as given by the "FXD_SLIT" keyword value, contains a
 point source, as given by the "SRCTYPE" keyword, it is necessary to know the
 photometric conversion factors for both a point source and a uniform source
@@ -96,7 +96,7 @@ is applied to the slit data, but that correction is not appropriate for the
 background signal contained in the slit, and hence corrections must be
 applied later in the :ref:`master background <master_background_step>` step.
 
-So in this case the `photom` step will compute 2D arrays of conversion
+In this case, the `photom` step will compute 2D arrays of conversion
 factors that are appropriate for a uniform source and for a point source,
 and store those correction factors in the "PHOTOM_UN" and "PHOTOM_PS"
 extensions, respectively, of the output data product. The point source
@@ -105,7 +105,7 @@ correction array is also applied to the slit data.
 Note that this special handling is only needed when the slit contains a
 point source, because in that case corrections to the wavelength grid are
 applied by the :ref:`wavecorr <wavecorr_step>` step to account for any
-source mis-centering in the slit and the photometric conversion factors are
+source offsets in the slit and the photometric conversion factors are
 wavelength-dependent. A uniform source does not require wavelength corrections
 and hence the photometric conversions will differ for point and uniform
 sources. Any secondary slits that may be included in a fixed-slit exposure

docs/jwst/pipeline/calwebb_spec3.rst

@@ -51,6 +51,9 @@ to observations of a moving target (TARGTYPE='moving').
 :sup:`2`\ The master background subtraction step is applied to NIRSpec MOS
 exposures in the :ref:`calwebb_spec2 <calwebb_spec2>` pipeline.
 
+WFSS and SOSS Processing
+------------------------
+
 Notice that NIRCam and NIRISS WFSS, as well as NIRISS SOSS data, receive only minimal
 processing by ``calwebb_spec3``.
 WFSS 2D input data are reorganized into source-based products by the
@@ -66,6 +69,19 @@ obtained in TSO mode.
 TSO mode NIRISS SOSS exposures should be processed with the
 :ref:`calwebb_tso3 <calwebb_tso3>` pipeline.
 
+Combined NIRSpec MOS and FS Exposures
+-------------------------------------
+
+It is possible to observe NIRSpec fixed slit targets alongside MSA
+slitlets in NIRSpec MOS exposures.  In this case, the input files produced by the
+:ref:`calwebb_spec2 <calwebb_spec2>` pipeline contain both MOS and FS data. Any
+:ref:`master_background <master_background_step>` corrections applied in this pipeline
+will operate on the fixed slits only, since background corrections for MOS slitlets should
+be applied in the :ref:`calwebb_spec2 <calwebb_spec2>` pipeline.  After the sources are
+separated in the :ref:`exp_to_source <exp_to_source>` step, each data product will contain
+only a fixed slit or a MOS target, so all further processing follows the standard flow
+for each exposure type.
+
 Arguments
 ---------