Description =========== :Class: `jwst.source_catalog.source_catalog_step.SourceCatalogStep` :Alias: source_catalog This step creates a catalog of source photometry and morphologies. Both aperture and isophotal (segment-based) photometry are calculated. Source morphologies are based on 2D image moments within the source segment. Source Detection ---------------- Stars are detected in the input image with one of the following source detection algorithms: `photutils.detection.DAOStarFinder`, `photutils.detection.IRAFStarFinder`, or `photutils.segmentation.SourceFinder`, in conjunction with `photutils.segmentation.SourceCatalog` (default). .. include:: ../references_general/source_detection.rst .. note:: If any other source detection algorithm other than `~photutils.segmentation.SourceFinder` is used, the output segmentation map will not be created, and the source catalog will be missing column values that are required for use as input to Level 2 spectral associations. Therefore if the direct image is to be used as part of a ``spec2`` association, `~photutils.segmentation.SourceFinder` should be used as the source detection algorithm. Source Photometry and Properties -------------------------------- After detecting sources, we can measure their photometry, centroids, and morphological properties. The aperture photometry is measured in three apertures, based on the input encircled energy values. The total aperture-corrected flux and magnitudes are also calculated, based on the largest aperture. Both AB and Vega magnitudes are calculated. The properties that are currently calculated for each source include source centroids (both in pixel and sky coordinates), isophotal fluxes (and errors), AB and Vega magnitudes (and errors), isophotal area, semimajor and semiminor axis lengths, orientation of the major axis, and sky coordinates at corners of the minimal bounding box enclosing the source. Photometric errors are calculated from the resampled total-error array contained in the ``ERR`` (``model.err``) array. Note that this total-error array includes source Poisson noise. Source Position --------------- The source centroid is computed as the center of mass of the unmasked pixels within the source segment (see `~photutils.segmentation.SourceCatalog` for details). As such, the centroid depends on the source morphology, the parameters passed to the segmentation algorithm, and the local background noise properties. This also makes the uncertainty in the centroid position difficult to estimate, and a formal error estimate is not provided by the step. Output Products --------------- Source Catalog Table ^^^^^^^^^^^^^^^^^^^^ The output source catalog table is saved in :ref:`ECSV format `. The table contains a row for each source, with the following default columns (assuming the default encircled energies of 30, 50, and 70): +------------------------+----------------------------------------------------+ | Column | Description | +========================+====================================================+ | label | Unique source identification label number | +------------------------+----------------------------------------------------+ | xcentroid | X pixel value of the source centroid (0 indexed) | +------------------------+----------------------------------------------------+ | ycentroid | Y pixel value of the source centroid (0 indexed) | +------------------------+----------------------------------------------------+ | sky_centroid | Sky coordinate of the source centroid | +------------------------+----------------------------------------------------+ | aper_bkg_flux | The local background value calculated as the | | | sigma-clipped median value in the background | | | annulus aperture | +------------------------+----------------------------------------------------+ | aper_bkg_flux_err | The standard error of the sigma-clipped median | | | background value | +------------------------+----------------------------------------------------+ | aper30_flux | Flux within the 30% encircled energy circular | | | aperture | +------------------------+----------------------------------------------------+ | aper30_flux_err | Flux error within the 30% encircled energy | | | circular aperture | +------------------------+----------------------------------------------------+ | aper50_flux | Flux within the 50% encircled energy circular | | | aperture | +------------------------+----------------------------------------------------+ | aper50_flux_err | Flux error within the 50% encircled energy | | | circular aperture | +------------------------+----------------------------------------------------+ | aper70_flux | Flux within the 70% encircled energy circular | | | aperture | +------------------------+----------------------------------------------------+ | aper70_flux_err | Flux error within the 70% encircled energy | | | circular aperture | +------------------------+----------------------------------------------------+ | aper_total_flux | Total aperture-corrected flux based on the 70% | | | encircled energy circular aperture; should be used | | | only for unresolved sources | +------------------------+----------------------------------------------------+ | aper_total_flux_err | Total aperture-corrected flux error based on the | | | 70% encircled energy circular aperture; should be | | | used only for unresolved sources | +------------------------+----------------------------------------------------+ | aper30_abmag | AB magnitude within the 30% encircled energy | | | circular aperture | +------------------------+----------------------------------------------------+ | aper30_abmag_err | AB magnitude error within the 30% encircled energy | | | circular aperture | +------------------------+----------------------------------------------------+ | aper50_abmag | AB magnitude within the 50% encircled energy | | | circular aperture | +------------------------+----------------------------------------------------+ | aper50_abmag_err | AB magnitude error within the 50% encircled energy | | | circular aperture | +------------------------+----------------------------------------------------+ | aper70_abmag | AB magnitude within the 70% encircled energy | | | circular aperture | +------------------------+----------------------------------------------------+ | aper70_abmag_err | AB magnitude error within the 70% encircled energy | | | circular aperture | +------------------------+----------------------------------------------------+ | aper_total_abmag | Total aperture-corrected AB magnitude based on the | | | 70% encircled energy circular aperture; should be | | | used only for unresolved sources | +------------------------+----------------------------------------------------+ | aper_total_abmag_err | Total aperture-corrected AB magnitude error based | | | on the 70% encircled energy circular aperture; | | | should be used only for unresolved sources | +------------------------+----------------------------------------------------+ | aper30_vegamag | Vega magnitude within the 30% encircled energy | | | circular aperture | +------------------------+----------------------------------------------------+ | aper30_vegamag_err | Vega magnitude error within the 30% encircled | | | energy circular aperture | +------------------------+----------------------------------------------------+ | aper50_vegamag | Vega magnitude within the 50% encircled energy | | | circular aperture | +------------------------+----------------------------------------------------+ | aper50_vegamag_err | Vega magnitude error within the 50% encircled | | | energy circular aperture | +------------------------+----------------------------------------------------+ | aper70_vegamag | Vega magnitude within the 70% encircled energy | | | circular aperture | +------------------------+----------------------------------------------------+ | aper70_vegamag_err | Vega magnitude error within the 70% encircled | | | energy circular aperture | +------------------------+----------------------------------------------------+ | aper_total_vegamag | Total aperture-corrected Vega magnitude based on | | | the 70% encircled energy circular aperture; | | | should be used only for unresolved sources | +------------------------+----------------------------------------------------+ | aper_total_vegamag_err | Total aperture-corrected Vega magnitude error | | | based on the 70% encircled energy circular | | | aperture; should be used only for unresolved | | | sources | +------------------------+----------------------------------------------------+ | CI_50_30 | Concentration index calculated as (aper50_flux / | | | aper30_flux) | +------------------------+----------------------------------------------------+ | CI_70_50 | Concentration index calculated as (aper70_flux / | | | aper50_flux) | +------------------------+----------------------------------------------------+ | CI_70_30 | Concentration index calculated as (aper70_flux / | | | aper30_flux) | +------------------------+----------------------------------------------------+ | is_extended | Flag indicating whether the source is extended | +------------------------+----------------------------------------------------+ | sharpness | The DAOFind source sharpness statistic | +------------------------+----------------------------------------------------+ | roundness | The DAOFind source roundness statistic | +------------------------+----------------------------------------------------+ | nn_label | The label number of the nearest neighbor | +------------------------+----------------------------------------------------+ | nn_dist | The distance in pixels to the nearest neighbor | +------------------------+----------------------------------------------------+ | isophotal_flux | Isophotal flux | +------------------------+----------------------------------------------------+ | isophotal_flux_err | Isophotal flux error | +------------------------+----------------------------------------------------+ | isophotal_abmag | Isophotal AB magnitude | +------------------------+----------------------------------------------------+ | isophotal_abmag_err | Isophotal AB magnitude error | +------------------------+----------------------------------------------------+ | isophotal_vegamag | Isophotal Vega magnitude | +------------------------+----------------------------------------------------+ | isophotal_vegamag_err | Isophotal Vega magnitude error | +------------------------+----------------------------------------------------+ | isophotal_area | Isophotal area | +------------------------+----------------------------------------------------+ | semimajor_sigma | 1-sigma standard deviation along the semimajor | | | axis of the 2D Gaussian function that has the same | | | second-order central moments as the source | +------------------------+----------------------------------------------------+ | semiminor_sigma | 1-sigma standard deviation along the semiminor | | | axis of the 2D Gaussian function that has the same | | | second-order central moments as the source | +------------------------+----------------------------------------------------+ | ellipticity | 1 minus the ratio of the 1-sigma lengths of the | | | semimajor and semiminor axes | +------------------------+----------------------------------------------------+ | orientation | The angle (degrees) between the positive X axis | | | and the major axis (increases counter-clockwise) | +------------------------+----------------------------------------------------+ | sky_orientation | The position angle (degrees) from North of the | | | major axis | +------------------------+----------------------------------------------------+ | sky_bbox_ll | Sky coordinate of the lower-left vertex of the | | | minimal bounding box of the source | +------------------------+----------------------------------------------------+ | sky_bbox_ul | Sky coordinate of the upper-left vertex of the | | | minimal bounding box of the source | +------------------------+----------------------------------------------------+ | sky_bbox_lr | Sky coordinate of the lower-right vertex of the | | | minimal bounding box of the source | +------------------------+----------------------------------------------------+ | sky_bbox_ur | Sky coordinate of the upper-right vertex of the | | | minimal bounding box of the source | +------------------------+----------------------------------------------------+ Note that pixel coordinates are 0 indexed, matching the Python 0-based indexing. That means pixel coordinate ``0`` is the center of the first pixel. Segmentation Map ^^^^^^^^^^^^^^^^ The segmentation map computed during the source finding process is saved to a single 2D image extension in a FITS file. Each image pixel contains an integer value corresponding to a source label number in the source catalog product. Pixels that don't belong to any source have a value of zero.