Enhanced Aperture Photometry in the JWST Pipeline Source Lists.

[stscijgbot]

Issue JP-1111 was created by Alicia Canipe:

 

Elaboration of Requirements for Aperture Photometry in the JWST Pipeline Source Lists.

(updated Nov 4, 2019 after JPWG discussion on Oct 9, 2019)

BACKGROUND:

Basic source lists requirements for the JWST pipeline were defined in:

[https://outerspace.stsci.edu/display/JWSTCC/Vanilla+Point+Source+Catalog]

This is sometimes referred to as the "Vanilla Source List". An "Optimal Source List" is also being discussed within the JWST Photometry Working Group and was presented to the Calibration Working Group in July 2019.

Below is an elaboration of the requirements for aperture photometry, as discussed within the JWST Photometry Working Group >>> webpage: [https://outerspace.stsci.edu/display/JWSTCC/JWST+Photometry+Working+Group]

REQUIREMENTS:

1. Circular aperture photometry should be performed using the Photutils package.

This can be in addition to the detection and photometry algorithms that are currently included in the pipeline code using an image segmentation approach, as long as this approach is able to identify point-like sources in different environments (e.g., high background, crowded regions) at a level that at least as good as with DAOPHOT. Early results from Larry Bradley's Jupyter handbook suggest this is true but this should be evaluated in more detail as we go along.

2. Aperture sizes in pixels should come from reference files developed by the NIRCAM, MIRI, and NIRISS instrument teams providing the pixel values for each instrument/filter combination that encircle 30 % - 50 % - 70 % of the energy in a PSF.

   • ** *** NOV 4, 2019 change >>>NOTE: 20 was change to 30 % on Nov 4, 2019, both here and below.

   • ** *** NOV 4, 2019 addition >>> Changes to the percentages used for certain instrument/filters combinations would be defined in configuration files, the development of which is TBD.

3. A local background should be used for sky subtraction based on the median value in a circular aperture taken between the 80 and 85 % encircled energy apertures, as defined in pixel values by the reference file described in item 2.

(NOTE: it is possible that the percentages defined in items 2 and 3 will be changed in the future, following a study of the optimal apertures.)

4. The format for the reference files should include aperture radii (in pixels as a function of detector/filter), and aperture corrections (to infinity) for each detector/filter combination. The aperture corrections should take into account the small contribution from the wings of the PSF in the sky annulus. A separate row should be used for each filter and encircled energy fraction.

Clarification from Larry Bradley in spring 2019 - " Right now, I simply need the aperture radii (in pixels) as a function of detector/filter. Once we have defined how many apertures to use in the output catalog, etc., I will define/deliver the initial version of the references files (one per instrument). The instrument teams can then redeliver updates as needed."

5. The source list should be optimized for point source detection, but should also do a reasonable job on somewhat extended sources. The finding algorithm should do reasonably well on all fields (e.g., stars, small galaxies like HDF, nearby galaxies with high backgrounds, ... ), rather than being tuned for a specific type of field.

(NOTE: A study may be needed to determine what the best values are for search parameters, e.g., FWHM, S/N, ... , and how well they work for different types of images).

6. The number of artifacts should be minimal. Typical artifacts include close pairs of stars, diffraction spikes, multiple detections of saturated cores, Airy rings, ...

7. Photometry with three units should be included in the catalog 1 - flux densities in Jy 2 - Vegamag in mag 3 - Abmags in mag

8. A single source list file should be produced providing the following information:

c1: X-position c2: Y-position c3: ID-number c4: RA c5: DEC

c6: fluxdens_30 (i.e., the flux density for the 30 % encircled energy aperture) c7: err_fluxdens_30 (error estimate in fluxdens_30) c8: fluxdens_50 c9: err_fluxdens_50 c10: fluxdens_70 c11: err_fluxdens_70 c12: back_fluxdens (median value in background annulus, tentatively planned for 80 - 85 % encircled energy aperture) c13: err_back_fluxdens (rms error estimate in back_fluxdens) c14: fluxdens_tot (total flux density if a star - set to NA if star? = N) c15: err_fluxdens_tot

c16: abmag_30 (i.e., the magnitude for the 30 % encircled energy aperture) c17: err_abmag_30 (error estimate in mag_30) c18: abmag_50 c19: err_abmag_50 c20: abmag_70 c21: err_abmag_70 c22: abmag_tot (total magnitude if a star - set to NA if star? = N) c23: err_abmag_tot

c24: vegamag_30 (i.e., the magnitude for the 30 % encircled energy aperture) c25: err_vegamag_30 (error estimate in mag_30) c26: vegamag_50 c27: err_vegamag_50 c28: vegamag_70 c29: err_vegamag_70 c30: vegamag_tot (total magnitude if a star - set to NA if star? = N) c31: err_vegamag_tot

c32: CI_30_80 (concentration index, i.e., the difference between mag_30 and mag_80, Note: other CIs can be determined based on other columns above) c33: star? (Is this a star? Y/N. e.g., . using a combination of the CI_30_50 and CI_50_80 and CI_30_80 values)

• ** *** NOV 4, 2019 - Quantitative values to be used for the stellar vs non-stellarr criteria will be provided at a later date based on analysis of the simulated images by the JPWG.

c34: sat_flag (saturation flag - Y/N - based on whether any pixels are saturated in full readout from the DQ array) c35: sharpness c36: roundness c37: major_axis c38: minor_axis c39: isolation metric

• ** *** NOV 4, 2019 - More explicit instructions to be used for the isolation criteria will be provided at a later date based on further discussions in the JPWG. A working example is "set isolation= no if there an object within the ee 80 % aperture that will affect the photometry at more than the 10 % level".

c40: sky_bbox_ll (RA/DEC for source bounding box corners for WFSS spectral pipeline) c41: sky_bbox_ul c42: sky_bbox_lr c43: sky_bbox_ur

NOTE: Other columns based on the image segmentation part of the code can also be included. (e.g., mag_auto, Kron_radius, ...)

• ** *** NOV 4, 2019 - Elaboration of the columns to include for the image segmentation part of the code will be discussed at a future JPWG meeting (probably Nov 13, 2019) and additional requirements may be added at that point. Some of the columns above that will probably come from this code are major-axis and minor_axis.

Question under consideration - If star? = no, should there be an estimate for total magnitude, since it could be misleading. At present the answer is no, with a NA = Not Applicable used for the relevant columns above. There was not a consensus on this item so it is still under discussion.

9. The catalog file should include a header that includes the information that does not vary (e.g., dataset used to obtain source list, date taken, aperture sizes used, filter used, ...) and that also explains the columns. There will be additional documentation available with more detailed descriptions.

 

 

 

 

=============

• ** *** Old Version below (replaced with newer version by Whitmore Nov 4)

Elaboration of Requirements for Aperture Photometry in the JWST Pipeline Source Lists

BACKGROUND:

Basic source lists requirements for the JWST pipeline were defined in:

[https://outerspace.stsci.edu/display/JWSTCC/Vanilla+Point+Source+Catalog]

This is sometimes referred to as the "Vanilla Source List". An "Optimal Source List" is also being discussed within the JWST Photometry Working Group and will be presented to the Calibration Working Group at a future date.

Below is an elaboration of the requirements for aperture photometry, as discussed within the JWST Photometry Working Group >>> webpage: [https://outerspace.stsci.edu/display/JWSTCC/JWST+Photometry+Working+Group]

REQUIREMENTS:

1. Circular aperture photometry should be performed using the Photutils package.

This can be in addition to the detection and photometry algorithms that are currently included in the pipeline code using an image segmentation approach, as long as this approach is able to identify point-like sources in different environments (e.g., high background, crowded regions) at a level that at least looks as good as with DAOPHOT. Early results from Larry Bradley's Jupyter handbook suggest this is true but this should be evaluated in more detail as we go along.

2. Aperture sizes in pixels should come from reference files developed by the NIRCAM, MIRI, and NIRISS instrument teams providing the pixel values for each instrument/filter combination that encircle 20 % - 50 % - 70 % of the energy in a PSF.

3. A local background should be used for sky subtraction based on the median value in a circular aperture taken between the 80 and 85 % encircled energy apertures, as defined in pixel values by the reference file described in item 2.

(NOTE: it is possible that the percentages defined in items 2 and 3 will be changed in the future, following a study of the optimal apertures.)

4. The format for the reference files should include aperture radii (in pixels as a function of detector/filter), and aperture corrections (to infinity) for each detector/filter combination. The aperture corrections should take into account the small contribution from the wings of the PSF in the sky annulus. A separate row should be used for each filter.

Clarification from Larry Bradley - " Right now, I simply need the aperture radii (in pixels) as a function of detector/filter. Once we have defined how many apertures to use in the output catalog, etc., I will define/deliver the initial version of the references files (one per instrument). The instrument teams can then redeliver updates as needed."

5. The source list should be optimized for point source detection, but should also do a reasonable job on somewhat extended sources. The finding algorithm should do reasonably well on all fields (e.g., stars, small galaxies like HDF, nearby galaxies with high backgrounds, ... ), rather than being tuned for a specific type of field.

(NOTE: A study may be needed to determine what the best values are for search parameters, e.g., FWHM, S/N, ... , and how well they work for different types of images).

6. The number of artifacts should be minimal. Typical artifacts include close pairs of stars, diffraction spikes, multiple detections of saturated cores, Airy rings, ...

7. Photometry with three units will be included in the catalog 1 - flux densities in Jy 2 - Vegamag in mag 3 - Abmags in mag

8. A single source list file should be produced providing the following information:

c1: X-position c2: Y-position c3: ID-number c4: RA c5: DEC

c6: fluxdens_20 (i.e., the flux density for the 20 % encircled energy aperture) c7: err_fluxdens_20 (error estimate in fluxdens_20) c8: fluxdens_50 c9: err_fluxdens_50 c10: fluxdens_70 c11: err_fluxdens_70 c12: back_fluxdens (median value in background annulus, tentatively planned for 80 - 85 % encircled energy aperture) c13: err_back_fluxdens (rms error estimate in back_fluxdens) c14: fluxdens_tot (total flux density if a star - set to NA if star? = N) c15: err_fluxdens_tot

c16: abmag_20 (i.e., the magnitude for the 20 % encircled energy aperture) c17: err_abmag_20 (error estimate in mag_20) c18: abmag_50 c19: err_abmag_50 c20: abmag_70 c21: err_abmag_70 c22: abmag_tot (total magnitude if a star - set to NA if star? = N) c23: err_abmag_tot

c24: vegamag_20 (i.e., the magnitude for the 20 % encircled energy aperture) c25: err_vegamag_20 (error estimate in mag_20) c26: vegamag_50 c27: err_vegamag_50 c28: vegamag_70 c29: err_vegamag_70 c30: vegamag_tot (total magnitude if a star - set to NA if star? = N) c31: err_vegamag_tot

c32: CI_20_80 (concentration index, i.e., the difference between mag_20 and mag80, Note: other CIs can be determined based on other columns above) c33: star? (Is this a star? Y/N. e.g., . using a combination of the CI 20_50 and CI_50_80 and CI_20_80 values) c26: sat_flag (saturation flag - Y/N - based on whether any pixels are saturated in full readout from the DQ array) c27: sharpness c28: roundness c29: major_axis c30: minor_axis c31: isolation metric (e.g., how roundness changes as function of radius ) Might use Leonardo's - nearest neighbor algorithm for this values

c32: sky_bbox_ll (RA/DEC for source bounding box corners for WFSS spectral pipeline) c33: sky_bbox_ul c34: sky_bbox_lr c35: sky_bbox_ur

NOTE: Other columns based on the image segmentation of the code can also be included. (e.g., mag_auto, Kron_radius, ...)

Question under consideration - If star? = no, should there be an estimate for total magnitude, since it could be misleading. At present the answer is no, with a NA = Not Applicable used for the relevant columns above. There was not a consensus on this item so it is still under discussion.

9. The catalog file should include a header that includes the information that does not vary (e.g., dataset used to obtain source list, date taken, aperture sizes used, filter used, ...) and that also explains the columns.

 

 

 

[stscieisenhamer]

jira issue valid but is not a code issue, as yet. closing.