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.

On this page

See also: Identifying Potential Duplicate Observations and JWST Duplication policy
Relevant Links outside of JDox: MAST Data Discovery Portal and JWST 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.

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:  Identifying Potential Duplicate Observations, and JWST Duplication Policy
Relevant Links outside of JDox: Summary listings of accepted GTO Program Information and ERS Program Information including links to the public APT files.

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, the information in these programs forms 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 in future cycles.

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.

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 no previously planned JWST observations are indicated by your check of MAST, no further checking is required.  (You're done!)   A check of MAST may also indicate whether previous data from HST or other missions are available for your target(s), which you may find useful.

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. However, the MAST Portal does not provide all of the information needed for duplication checking. Hence, you will need to inspect the detailed information in the APT files from any indicated JWST programs to assess the details on the instrument configuration(s) and exposure times being requested.   

 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 by the JWST project 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. 

With the APT file open, 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 to avoid the duplication.

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 by the accepted proposer.  Hence, specific duplications are unknowable at proposal time.  See the JWST Duplication Policy for details.


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. 



Latest updates
  • Removed duplications with JWST Duplication Policy article.
  •  Article streamlined by removing redundancy and duplicate linking.