JP-3605: Change default value for abs_separation in the tweakreg step (…

…#8445)

Co-authored-by: Nadia Dencheva <nadia.dencheva@gmail.com>

CHANGES.rst

@@ -23,7 +23,7 @@ associations
   and dither pointing, ``MOSTILNO`` and ``DITHPTIN``. [#8410]
 
 dark_current
-------------  
+------------
 
 - Add log info message when specifying an average_dark_current for noise calculations.
   [#8425]
@@ -33,7 +33,7 @@ documentation
 
 - Added docs for the NIRSpec MSA metadata file to the data products area of RTD.
   [#8399]
-  
+
 - Added documentation for multiprocessing. [#8408]
 
 extract_1d
@@ -104,6 +104,9 @@ tweakreg
 
 - Improved how a image group name is determined. [#8426]
 
+- Changed default settings for ``abs_separation`` parameter for the ``tweakreg``
+  step to have a value compatible with the ``abs_tolerance`` parameter. [#8445]
+
 
 1.14.0 (2024-03-29)
 ===================

docs/jwst/tweakreg/README.rst

@@ -21,8 +21,8 @@ format automatically recognized by :py:meth:`~astropy.table.Table.read`.
 When the ``meta.tweakreg_catalog`` attribute of input data models is `None` or
 an empty string, then the ``tweakreg`` step will attempt to detect sources in the
 input images. Stars are detected in the image with one of the following source
-detection algorithms: ``photutils.detection.DAOStarFinder`` (default), 
-``photutils.detection.IRAFStarFinder``, or ``photutils.segmentation.SourceFinder`` 
+detection algorithms: ``photutils.detection.DAOStarFinder`` (default),
+``photutils.detection.IRAFStarFinder``, or ``photutils.segmentation.SourceFinder``
 in conjunction with ``photutils.segmentation.SourceCatalog``.
 
 DAOStarFinder is an implementation of the `DAOFIND`_ algorithm
@@ -38,26 +38,26 @@ specified.
 IRAFStarFinder is a Python implementation of the IRAF star finding algorithm,
 which also calculates the objects' centroids, roundness, and sharpness.
 However, IRAFStarFinder uses image moments
-instead of 1-D Gaussian fits to projected light distributions like 
+instead of 1-D Gaussian fits to projected light distributions like
 DAOStarFinder.
 
 SourceFinder implements a segmentation algorithm that identifies
-sources in an image based on a number of connected pixels above a 
-specified threshold value.  The sources are deblended using a 
-combination of multi-thresholding and watershed segmentation. 
+sources in an image based on a number of connected pixels above a
+specified threshold value.  The sources are deblended using a
+combination of multi-thresholding and watershed segmentation.
 SourceCatalog finds the centroids of these sources, which are used
-as the retrieved star positions. 
+as the retrieved star positions.
 
 .. warning::
-    It has been shown (`STScI Technical Report JWST-STScI-008116, SM-12 
-    <https://www.stsci.edu/~goudfroo/NIRISSdoc/Centroid_Accuracies_Precisions_NIRISS_v2.pdf>`_) 
+    It has been shown (`STScI Technical Report JWST-STScI-008116, SM-12
+    <https://www.stsci.edu/~goudfroo/NIRISSdoc/Centroid_Accuracies_Precisions_NIRISS_v2.pdf>`_)
     that for undersampled PSFs, e.g. for short-wavelength NIRISS
     imaging data, ``DAOStarFinder`` gives bad results no matter the input parameters
     due to its use of 1-D Gaussian fits.
     ``IRAFStarFinder`` or ``SourceFinder`` should be used instead.
 
-.. note:: 
-    ``SourceFinder`` is likely to detect non-stellar sources 
+.. note::
+    ``SourceFinder`` is likely to detect non-stellar sources
     such as galaxies because sources are not assumed to be
     point-source-like. This may lead to mismatches between the
     derived source catalog and the reference catalog during the
@@ -254,7 +254,7 @@ The ``tweakreg`` step has the following optional arguments:
 
 **Additional source finding parameters for segmentation:**
 
-* ``npixels``: An `int` value indicating the minimum number of 
+* ``npixels``: An `int` value indicating the minimum number of
   connected pixels that comprises a segment (Default=10)
 
 * ``connectivity``: An `int` value indicating the connectivity defining the
@@ -280,7 +280,7 @@ The ``tweakreg`` step has the following optional arguments:
   Allowed values: `'correct'`, `'mask'`, `'none'`. (Default= `'correct'`)
 
 * ``kron_params``: A tuple of `float` values indicating the
-  parameters defining Kron aperture. If None, 
+  parameters defining Kron aperture. If None,
   the parameters `(2.5, 1.4, 0.0)` are used. (Default=None)
 
 **Optimize alignment order:**
@@ -374,9 +374,7 @@ Parameters used for absolute astrometry to a reference catalog.
   Otherwise the initial guess for the offsets will be set to zero
   (Default=True)
 
-* ``abs_separation``: Minimum object separation in arcsec. It is recommended
-  that a value smaller than ``separation`` be used for this parameter
-  (e.g. 10 times smaller) (Default=0.1)
+* ``abs_separation``: Minimum object separation in arcsec. (Default=1.0)
 
 * ``abs_tolerance``: Matching tolerance for ``xyxymatch`` in arcsec.
   (Default=0.7)

jwst/tweakreg/tweakreg_step.py

@@ -97,7 +97,7 @@ class TweakRegStep(Step):
         abs_searchrad = float(default=6.0) # The search radius in arcsec for a match when performing absolute astrometry
         # We encourage setting this parameter to True. Otherwise, xoffset and yoffset will be set to zero.
         abs_use2dhist = boolean(default=True) # Use 2D histogram to find initial offset when performing absolute astrometry?
-        abs_separation = float(default=0.1) # Minimum object separation in arcsec when performing absolute astrometry
+        abs_separation = float(default=1) # Minimum object separation in arcsec when performing absolute astrometry
         abs_tolerance = float(default=0.7) # Matching tolerance for xyxymatch in arcsec when performing absolute astrometry
         # Fitting geometry when performing absolute astrometry
         abs_fitgeometry = option('shift', 'rshift', 'rscale', 'general', default='rshift')