Breaking News

Major events or changes in the JWST mission are posted in this article. As of July 2022, changes and new information available at the end of commissioning and as the mission transitions to science operations, are highlighted for the community

July 12, 2022 initial post-commissioning news

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Please note the following:

  • For a list of new JDox articles and updates to existing articles, please go to JWST JDox Latest Updates

  • Since commissioning has just concluded, it will take time to fully process what has been learned and to propagate that information into JDox. We have placed temporary warning banners on the most important pages where we are still awaiting updates from commissioning to warn users when pre-flight data are still being shown.

  • At the bottom of each article is a table that has information on when a page was published and when notable updates have been made. Get in the habit of checking those dates to know when updates have been made!

  • Updates will be added as appropriate over the summer and and early fall of 2022 in preparation for the Cycle 2 Call for Proposals. Stay tuned!

JWST science performance report at the end of commissioning

A report on the actual JWST science performance, as characterized through the 6-month commissioning activities, is now available.

The JWST commissioning team has prepared a detailed report describing JWST's science performance as characterized in commissioning.  The report provides an excellent summary of the observatory and science instrument performance as it is known at the end of commissioning. Several highlights of most interest to observers include:

  • Slewing and pointing performance is as good or better than pre-mission expectations and guide star acquisitions are working well. Guiding performance is also excellent, with the pointing stability of the line of sight under fine guidance control several times better than the requirement. See section 2.4 and all of section 3 of the report.

  • The science instruments are meeting or exceeding their requirements (see section 6 of the report). Overall throughput is generally higher than pre-mission expectations, with up to 30% increased sensitivity for some instrument modes and wavelengths. This has at least 2 ramifications of interest to the user community:

    • Until full sensitivity details are known from commissioning, which will enable proper updates to the Exposure Time Calculator (ETC) and JWST Interactive Sensitivity Tool (JIST), these tools will generally underpredict actual performance in most cases. Both tools will be updated prior to the Cycle 2 Call for Proposals.

    • At this time, the JWST Project is not recommending that observers update their programs or their APT files for this effect since the signal-to-noise ratio in observations will usually be higher than predicted. The only exception is for very bright targets that were predicted to saturate in the second group (and that could now, in principle, saturate within the first group). Any programs containing such targets should be carefully reconsidered prior to observation. For questions or concerns, please contact your program coordinator or the JWST Help Desk.

  • The JWST background levels are a combination of multiple components that vary with time, orientation, wavelength, and observatory conditions. It will take time to fully characterize these components and their variability, and to get the changes into the various planning tools. However, commissioning data are largely consistent with predictions; if anything, near-IR backgrounds may be somewhat lower than expected.  See section 5 of the report for details.

Artifacts seen in JWST data

See also: Data Features and Artifacts

In-flight experience has identified a number of artifacts and features that may appear in data, depending on circumstances at the time a given data set was obtained. Some of these effects are seen in data from multiple instruments while others are specific to a given instrument. The Data Features and Artifacts article has pointers to currently available information.

The user community will certainly want to be on the lookout for any of these features in science data and identify them appropriately. If you see anomalies in your data, contact the JWST Help Desk, as ongoing operations can help STScI characterize and possibly mitigate these effects going forward.

Caveats and limitations of the science calibration pipeline

See also: Section 7 of the commissioning report linked above.

At this early stage of the mission with the current operational pipeline and available reference files, calibration products may show a variety of known issues that produce poor registration of images, double spectral lines, or other effects that may limit their usefulness for scientific analysis. Also, users should note that early data available from MAST may have been processed with pre-flight calibration data and will require reprocessing with in-flight files to produce science-quality results. Instrument teams will continue working as quickly as possible during the early science operations period to finish updating the reference files with in-flight data obtained during commissioning, and later on with data obtained during Cycle 1 calibration programs. See the JWST Calibration Pipeline Caveats article and references therein for more information.

The JWST Science Calibration Pipeline software performs nominal processing of JWST data for the many different instruments and instrument modes, making science-ready data products available to users. However, early in the mission, the pipeline software as well as the available calibration reference files are expected to be dynamic, with the scheduling of new software builds as experts implement improvements to the current algorithms or address features and artifacts found during in-flight operations. However, even with these improvements, it is impossible to accommodate certain specialized data processing schemes within the context of a standard pipeline processing system. The bottom line for JWST users is that early data will likely need to be reprocessed as improved information becomes available.

Science data will be reprocessed periodically as new versions of the JWST Science Calibration Pipeline are released and/or as new reference files become available. Use the MAST Portal to subscribe to observations of interest; you will then receive notifications when recalibrated products appear in the Archive for that observation. See the "Program Subscriptions and Notificationschapter of the MAST Portal Users Guide for information on how to subscribe. 

If your data were reprocessed due to changes in the JWST Science Calibration Pipeline, please refer to this article, JWST Pipeline Build Information, for release notes about those software changes.

In this release of JDox (on July 12, 2022), STScI is publishing a suite of articles outlining the currently known caveats and limitations of the pipeline products for many of the various instrument modes. New articles will be added and the existing articles will be updated as more information becomes available, so check back frequently. 

Because of the dynamic nature of the science calibration pipeline, as well as frequent reference file updates early in the mission, early JWST publications should include the CAL_VER and CRDS_CTX entries from the relevant data headers so that future researchers can reproduce results and retrospectively assess calibration issues or the need to recalibrate the data. See the JWST Calibration Pipeline Caveats article for more details.

A heads-up to NIRSpec MOS/MSATA users

See also: NIRSpec MPT - Catalogs and NIRSpec MSA Target Acquisition

Initial experience with the NIRSpec MOS observing highlights the need for careful vetting of the astrometry derived from pre-imaging against source positions in the Gaia catalog. In particular, the MSA target acquisition procedure has a very limited ability to correct for errors in the initial roll, and so it is essential that the rotation of the reference stars on the sky be aligned with that of the Gaia frame to better than 30” in rotation. Care should be taken to consider any proper motion of the Gaia stars and reference stars to avoid introducing a spurious roll offset larger than this. Early NIRCam pre-imaging observations are included in this requirement until camera distortions are better characterized and included in the NIRCam data processing pipeline. Since this is a dynamic area with ongoing development, it is best to contact your program coordinator and NIRSpec instrument scientist or the JWST Help Desk for more details.

JWST data analysis tool (JDAT) video tutorials now available

All early release observations (ERO) and commissioning data become public during the ERO release on July 12, 2022. Also, as Directors Discretionary Early Release Science program data are obtained (primarily over the first 5 months of science operations), those data will immediately be publicly available. You are encouraged to grab some public data and investigate it!

A number of new videos on the JWST data analysis tools suite (JDAT; Imviz, Specviz, and Cubeviz) are posted at the JWST Observer YouTube channel. A convenient tabular listing with summary descriptions and direct links to each video is now available at JWST Data Analysis Tool Video Tutorials.

Users may also refer to the videos and support materials from the previous JWebbinar series (open the "Materials and Videos" tab) to get started on working with JWST data.

Looking for JWST data?

Everything you need to get started is available from the Accessing JWST Data article. Don't forget to check the pedigree of existing data in MAST by checking the CRDB context of the calibration files applied to the data set of interest. See the JWST Calibration Pipeline Caveats article (and in particular, the section on CRDS reference file status) for details. Good luck!

Publishing JWST data

As a reminder, when publishing JWST data, please remember to add the appropriate standard acknowledgements, examples of which are shown in MAST.  Also, paper authors are obliged to include a digital object identifier (DOI) that points to the data they analyzed. Instructions for doing that can be found in the Special Searches article that is part of the MAST Portal Guide.

The JWST Director's Discretionary Time program

Coinciding with the July 12, 2022 release of Early Release Observations, the opportunity to propose for JWST Director’s Discretionary Time (DDT) has been opened to the astronomy community! Consistent with the policies for DDT proposals, they should be proposed for time-critical observations that are unable to wait to go through the regular TAC process.

Cycle 2 Guaranteed Time Observer call for proposals

JWST Guaranteed Time Observers (GTOs) are invited to submit Cycle 2 GTO science proposals. The details for submitting proposals can be found in the JWST Cycle 2 GTO Call for Proposals, which has just been released. 




Latest updates
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    Added pointer to DOI information in the Publication section
Originally published