JP-2922: Minor fixes for MSA source names

CHANGES.rst

@@ -22,7 +22,7 @@ assign_wcs
 
 - Updated the routines that load NIRSpec MOS slit and source data from the MSA meta
   data file to properly handle background and virtual slits, and assign appropriate
-  meta data to them for use downstream. [#8442]
+  meta data to them for use downstream. [#8442, #8533]
 
 associations
 ------------
@@ -103,6 +103,13 @@ general
 
 - Increase minimum required scipy. [#8441]
 
+master_background_mos
+---------------------
+
+- Updated check for NIRSpec MOS background slits to use new naming convention:
+  ``slit.source_name`` now contains the string "BKG" instead of
+  "background". [#8533]
+
 outlier_detection
 -----------------
 

jwst/assign_wcs/nirspec.py

@@ -674,7 +674,13 @@ def get_open_msa_slits(prog_id, msa_file, msa_metadata_id, dither_position,
                     (s['source_name'], s['alias'], s['stellarity'], s['ra'], s['dec'])
                     for s in msa_source if s['source_id'] == source_id][0]
             except IndexError:
-                log.warning("Could not retrieve source info from MSA file")
+                source_name = f"{prog_id}_VRT{slitlet_id}"
+                source_alias = "VRT{}".format(slitlet_id)
+                stellarity = 0.0
+                source_ra = 0.0
+                source_dec = 0.0
+                log.warning(f"Could not retrieve source info from MSA file; "
+                            f"assigning virtual source_name={source_name}")
 
             if source_id < 0:
                 log.info(f'Slitlet {slitlet_id} contains virtual source, with source_id={source_id}')

jwst/assign_wcs/tests/test_nirspec.py

@@ -4,6 +4,7 @@
 import functools
 from math import cos, sin
 import os.path
+import shutil
 
 import pytest
 import numpy as np
@@ -355,6 +356,35 @@ def test_msa_configuration_multiple_returns():
     _compare_slits(slitlet_info[1], ref_slit2)
 
 
+def test_msa_missing_source(tmp_path):
+    """
+    Test the get_open_msa_slits function with missing source information.
+    """
+    # modify an existing MSA file to remove source info
+    msaconfl = get_file_path('msa_configuration.fits')
+    bad_confl = str(tmp_path / 'bad_msa_configuration.fits')
+    shutil.copy(msaconfl, bad_confl)
+
+    with fits.open(bad_confl) as msa_hdu_list:
+        source_table = table.Table(msa_hdu_list['SOURCE_INFO'].data)
+        source_table.remove_rows(slice(0, -1))
+        msa_hdu_list['SOURCE_INFO'] = fits.table_to_hdu(source_table)
+        msa_hdu_list[3].name = 'SOURCE_INFO'
+        msa_hdu_list.writeto(bad_confl, overwrite=True)
+
+    prog_id = '1234'
+    msa_meta_id = 12
+    dither_position = 1
+
+    slitlet_info = nirspec.get_open_msa_slits(
+        prog_id, bad_confl, msa_meta_id, dither_position, slit_y_range=[-.5, .5])
+
+    # MSA slit: virtual source name assigned
+    ref_slit = trmodels.Slit(55, 9376, 1, 251, 26, -5.6, 1.0, 4, 1, '1111x',
+                             '1234_VRT55', 'VRT55', 0.0,
+                             -0.31716078999999997, -0.18092266, 0.0, 0.0)
+    _compare_slits(slitlet_info[0], ref_slit)
+
 open_shutters = [[24], [23, 24], [22, 23, 25, 27], [22, 23, 25, 27, 28]]
 main_shutter = [24, 23, 25, 28]
 result = ["x", "x1", "110x01", "110101x"]

jwst/master_background/master_background_mos_step.py

@@ -191,7 +191,7 @@
         # count how many are background vs source.
         num_bkg = num_src = 0
         for slit in data.slits:
-            if "background" in slit.source_name:
+            if nirspec_utils.is_background_msa_slit(slit):
                 num_bkg += 1
             else:
                 num_src += 1

jwst/master_background/nirspec_utils.py

@@ -101,7 +101,7 @@
     bkg_model.update(input_model)
     slits = []
     for slit in input_model.slits:
-        if "background" in slit.source_name:
+        if is_background_msa_slit(slit):
             log.info(f'Using background slitlet {slit.source_name}')
             slits.append(slit)
 
@@ -242,3 +242,23 @@
         input_model.data *= (pl_uniform / pl_point)
 
     return input_model
+
+
+def is_background_msa_slit(slit):
+    """
+    Check if an MSA slitlet is a background source.
+
+    Parameters
+    ----------
+    slit : `~jwst.datamodels.SlitModel`
+        The slit model to check.
+
+    Returns
+    -------
+    bool
+        True if the slit is background; False if it is not.
+    """
+    if "BKG" in str(slit.source_name).upper():
+        return True
+    else:
+        return False

jwst/master_background/tests/test_nirspec_corrections.py

@@ -2,11 +2,12 @@
 Unit tests for master background NIRSpec corrections
 """
 import numpy as np
+import pytest
 
 from stdatamodels.jwst import datamodels
 
 from jwst.master_background.nirspec_utils import (
-    correct_nrs_ifu_bkg, correct_nrs_fs_bkg
+    correct_nrs_ifu_bkg, correct_nrs_fs_bkg, is_background_msa_slit
 )
 
 
@@ -54,3 +55,15 @@ def test_fs_correction():
     result = correct_nrs_fs_bkg(input, primary_slit=True)
 
     assert np.allclose(corrected, result.data, rtol=1.e-7)
+
+
+@pytest.mark.parametrize('name,status',
+                         [('BKG101', True), ('bkg101', True),
+                          ('background_101', False), ('101', False),
+                          (None, False)])
+def test_is_background(name, status):
+    """Test check for background slit."""
+    slit = datamodels.SlitModel()
+    if name is not None:
+        slit.source_name = name
+    assert is_background_msa_slit(slit) == status