Webb Office Hours Session 42: December 11, 2025
Q&A's:
Q1: Where are the Webb Office Hours procedures and guidelines?
A1: Webb Office Hours. Type your question into the WebEx chat. We will asynchronously copy questions from the chat to this main page and work through them as a group. If you have images to share please give WebEx permission to share your screen (you may need to log out and log back in again to enable this feature.)
Q2: I am working with some MIRI MRS data that has multiple point sources in my cubes and I want to extract them separately, but between cubes of different channels and bands the source centroid is at a slightly different pixel in the cube. How can I change the extraction aperture center for each channel/band can I set this in the extract_1d reference file?
A2: The extract_1d reference file for MIRI MRS allows you to set changing extraction aperture radius and inner/outer background annuli, as a function of wavelength, but it does not allow you to set the aperture center. The aperture center for MRS extraction can be set through the center_xy parameter in extract_1d (see https://jwst-pipeline.readthedocs.io/en/latest/jwst/extract_1d/arguments.html#step-arguments-for-ifu-data for details). This parameter allows you to set the x/y pixel center of your extraction aperture, but if you are seeing a slight change in the position of your source between cubes from different channels/bands, you may need to loop through each cube and extract your sources with a different input to the center_xy parameter. One way you might be able to automate this is by using the source position (in RA/Dec) as a first guess, find the nearest PSF centroid in IFU pixels, and use that position as the aperture center to extract your source with the extract_1d step.
If instead you need to have an extraction aperture that moves with wavelength within a cube, this would require doing a custom extraction outside of the pipeline, as the pipeline does not currently support changing the extraction aperture centering within a given cube as a function of wavelength.
Q3: For my MIRI MRS data there are options for master_background subtraction and background subtraction can be done during spectral extraction, how should I use them together?
A3: If you have performed a master_background subtraction you may not need to additionally perform an annular background subtraction during spectral extraction, because the background, in principle should have been subtracted off already. The one possible exception to this may be if there are local variations in the background across your cube that have not been subtracted by the master_background step, in which case you may additionally want to subtract the background during extraction.
There is also a pixel-by-pixel background subtraction that can be done with dedicated background observations in the calwebb_spec2 pipeline processing, so you may want to explore different options for performing background subtraction with each of these different options to see which works best for your science case.
Q4: I am new to JWST and currently exploring the data calibration pipeline and using JWST data. Could you please provide some resources on the pipeline and how I can get in touch with experts if I run into issues?
A4:
Basic overview of the JWST calibration pipeline: https://jwst-docs.stsci.edu/jwst-science-calibration-pipeline#gsc.tab=0
JWST calibration pipeline repository: https://github.com/spacetelescope/jwst
Here is a summary of the JWST calibration pipeline notebooks that show how to do a custom reprocessing of JWST data: https://jwst-docs.stsci.edu/jwst-science-calibration-pipeline/jwst-pipeline-notebooks#gsc.tab=0
You may also submit questions to the JWST Help Desk: jwsthelp.stsci.edu (you need to create a MyST account)
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