JWST Duplication Checking

Users are responsible for checking their proposed observations for potential duplications against accepted or previously executed observations, and either removing the duplication or explaining any such potential duplications in their science proposals.

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See also: Identifying Potential Duplicate Observations 
See also: JWST Duplication policyMAST Data Discovery PortalJWST Program ID Look-up GUI

As part of maximizing the science return of JWST, unnecessary duplication of observations needs to be avoided. Proposed observations that duplicate or potentially duplicate existing or planned observations must be scientifically justified by the proposer.  The JWST Duplication Policy defines what constitutes a duplication. In short, a proposed observation is a duplication if the following are true:  

(a) same source or field; 
(b) same or similar instrument;
(c) same mode or template;
(d) similar (within a defined factor) exposure time or signal-to-noise ratio; and
(e) for spectral modes, similar spectral resolution and/or significantly overlapping spectral coverage.

Duplication checking prior to submission is the user's responsibility.  Any duplications or potential duplications (for programs where the details are not known up front) must be discussed and/or justified in the text of the proposal. Failure to do so may result in the rejection of the proposed observation even after proposal acceptance.  For accepted proposals, STScI will perform a detailed duplication check to catch and remove any duplications within the current pool of accepted proposals.

Pre-submission checking

See also: Summary listings of GTO Program Information and ERS Program Information 

To avoid unintentional duplications, proposers will be required to check their proposed observations against those already approved (both in the queue and previously observed).  For cycle 1 general observers, there are no existing observations, but Guaranteed Time Observer (GTO) proposals  and Early Release Science (ERS) proposals have already been accepted, and must not be duplicated without a sound scientific justification.  Hence, these form the basis of potential duplications for Cycle 1. Of course, as JWST observations are obtained and archived, the observations will go into the Mikulski Archive for Space Telescopes (MAST) and will also be available for duplication checking.

The MAST Data Discovery Portal will assist you in making these checks for potential duplications in a straightforward way, allowing you to quickly see whether your proposed targets have any previously approved JWST observations. Details are provided in the article Identifying Potential Duplicate Observations.

If potential duplications are indicated by the MAST Discovery Portal check, refer to the accepted JWST program APT files and the Aladin visualization tool for the detailed information needed to fully assess possible duplications. MAST provides direct links to the JWST programs of interest.

Note that targets are not protected, but rather observations of targets with a particular instrument,instrument mode and requested S/N are protected against unjustified duplications. Hence, you will need to inspect the detailed information from any indicated JWST programs to assess the details on the instrument configuration(s) and exposure times being requested.

The MAST Portal does not provide all of the information needed for duplication checking.  Rather, when the MAST interface shows that a JWST observation has been proposed, the JWST program numbers will be highlighted with links that will take you to the program information page for that program.  These linked pages include access to both the formatted public PDF file of each program and to the actual APT files of each program.

Viewing Accepted Program Details

There are several ways to connect to more detailed information about accepted JWST programs.

1) Peruse the convenient listings of program IDs and titles provided for ERS and GTO programs. Clicking the program ID in these listings will connect you to a Program Information page for that program, including links to both the public PDF file and to the APT file itself.

2) Alternatively, a valid accepted program ID number can be typed directly into the JWST Program Information tool to get to the program information.

3) Finally, the APT files for accepted programs can be loaded directly into an APT session. With APT open, go to the top File pull down menu, select Retrieve from STScI → Retrieve using Proposal ID, and enter the program ID in the box provided.  Viewing the program details and using the Aladin interface to view mosaics and dithers will then allow you to check in detail what was being proposed for comparison with your own plans.

In summary, here is a process you can follow for duplication checking:

  • Use the MAST Discovery Portal to search for an object of interest, following the guidelines in Identifying Potential Duplicate Observations.
  • If you find corresponding JWST observations of the target, click on the highlighted program number to access the program summary information.
  • For a quick look, download the program PDF file, which provides a formatted summary of the program. If more details are needed, download the APT file (or load the program from within APT) for more detailed inspection.
    • Alternatively, go to JWST Program ID Look-up tool and enter the relevant program ID or IDs to access the PDF or APT file.
  • Specifically, check the instrument mode, filters/gratings, dithers and total exposure time, and any other details relevant to the mode you are proposing to assess whether a likely duplication is being considered.
    • If desired, display relevant observations in Aladin to see the full dither pattern or mosaic being proposed.
  • If any duplications with your planned observations are identified, either justify the need for new data or adjust your proposed observing plan accordingly.

Some cases will be complicated enough that you can only discuss that a potential duplication exists.  The prime example is NIRSpec MSA observations, where the specific objects for observation are not selected until a final MSA configuration is determined. In this case, you should simply note the overlap of the proposed observation with an existing observation, and (assuming your proposal is accepted) the details will be assessed later in the scheduling process.  See the JWST Duplication Policy for details.

Note: You may want to perform this duplication checking step prior to going through the effort of entering and validating your own APT proposal, to avoid the potential of finding out after the fact that duplications had already been proposed.  Of course, if there is a scientific justification for a duplication, such as a time-variable source or need for higher signal-to-noise that in the original observation, you can still request it, but you should provide the details in your science proposal text.


Post-acceptance checking

Once a proposal is accepted, one of the first steps in proposal processing is a duplication check performed by STScI personnel. Their software not only checks for duplications against previous and planned observations, but also checks within the pool of accepted programs for a given cycle to catch any potential duplications.  STScI personnel will contact affected PIs to resolve any such duplications if they occur. Any duplications found against previous or planned observations that were not revealed by the PI and explicitly approved by the TAC and STScI director may be disallowed and the program's resource allocation decreased accordingly.  



Latest updates

  • Significant revisions; article now describes the final duplication checking process for Cycle 1.