Webb Office Hours Session 23:  February 13, 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 have NIRCam imaging data of the galactic center taken in many filters. I have made progress running the pipeline using the 1/f correction, clean_flicker_noise step, to reduce the noise, but I still have regions that have a lot of noise.  Is there something else I can try?

A2:  The noise you have still looks like 1/f noise.  This can be very hard to correct in fields with lots of diffuse emission.  There are a lot of options that you can try to reduce the noise further.  Please see this JDox page on the best suggestions we have for NIRCam data, especially the recommendations for fields with extended emission: https://jwst-docs.stsci.edu/known-issues-with-jwst-data/nircam-known-issues/nircam-1-f-noise-removal-methods#NIRCam1/fNoiseRemovalMethods-Imagingmode

Right now your background method is set to 'median' (in the clean_flicker_noise step).  You can try setting it to model to see if this reduces the noise.  If it doesn't, you may have to play around with the size of the box using 'background_box _size'.  You can find the documentation of the step arguments here: https://jwst-pipeline.readthedocs.io/en/stable/jwst/clean_flicker_noise/arguments.html

Another thing to try is to do different correction methods region by region in your image.  So in the one area of your image that is still giving you problems you can try to just work on this region and it won't affect the other regions that you've already successfully reduced the noise in. 

Finally, you can also try using some tools from the community that may further help reduce the noise: https://jwst-docs.stsci.edu/known-issues-with-jwst-data/nircam-known-issues/nircam-1-f-noise-removal-methods/alternative-1-f-noise-software-packages#gsc.tab=0

Q3: Sometimes when I rerun the pipeline with updated parameters it is worse than the default that I got from MAST in some filters.  What is happening here? Am I doing something wrong when running the pipeline?

A3:  The needs of every filter are different.  So if you optimize for one filter by changing the pipeline parameters it may negatively affect another filter. It looks like you may also have an alignment issue that is different between filters, so may want to look into what catalog it is using as well. 

Q4: I would like to try to subtract the stars using WebbPSF, is this a good idea?

A4:  Yes, WebbPSF models are in good shape for NIRCam, so if you can model the stars with the SEDs then this could be a good idea. 
Please note WebbPSF is now called STPSF: https://www.stsci.edu/jwst/science-planning/proposal-planning-toolbox/psf-simulation-tool, https://stpsf.readthedocs.io/en/latest/#

Q5: FYI: When I run the pipeline notebooks with a large number of files it runs everything, but then just hangs and I have to stop it myself.  This does not happen when I run it with a smaller number of files.

A5: Thank you for alerting us of this issue.  This is likely a memory issue.  We have flagged this as an issue and will look into it as soon as possible. 

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