Coordinated Parallels Roadmap

A step-by-step guide through the process of adding coordinated parallel observations to an observing program for JWST.

Coordinated parallel observations must be scientifically justified.  See the NASA policy for coordinated parallels.

Not all instrument pairings are allowed, and in some cases the primary and parallel instruments are not interchangeable.  See the allowed pairings.

1. What instrument pairing is needed for your science, and which instrument will be specified as “primary” and “parallel”?  Even if both instruments are equally important, one must be specified as the primary in APT.

2. Work with the ETC to understand the relative exposure times needed for both instruments.  If possible, you may wish to make the instrument requiring longer exposures to be your primary instrument since your parallel instrument exposures, which must be paired with the primary exposures, need to fit within the primary exposure times. 

3. Understand what you plan to do with dithering, since this will need to be coordinated between both the primary and parallel instrument.  Most imaging parallel modes have dither patterns that will work for both instruments.  Parallels with NIRSpec MOS must simply adopt the MOS dither or nod pattern of the primary NIRSpec observation.  See [coord parallel article] where this is discussed.

4.  Enter the information for the primary instrument exposure specifications into the appropriate APT observing template.  If this is an imaging mosaic, you may want to verify mosaic details by using the  Aladin visualization tool.  In any event, you should verify the schedulability of your primary observation using the APT Visit Planner and address any scheduling issues prior to adding your desired coordinated parallel specifications.

5. Once the primary instrument specifications are verified, find and select the “coordinated parallel” checkbox in the APT observation templates that allow parallels.  Then select the desired parallel instrument and mode.

6.  Open the parallel instrument tab in the observing template and fill out the exposure specifications for your parallel instrument.  There needs to be a one-to-one match between primary and parallel exposures.  Hint: hover the cursor over any red X’s for help in resolving any errors reported by APT.  It can take some iteration to make APT happy.

7. Once errors are resolved, run the Visit planner again to verify schedulability.

Using NIRCam or NIRISS Slitless spectroscopy (Grism) modes in parallel:  Specifying these modes in parallel is complicated by the need to take direct images before and/or after the Grism exposures. See [the article on parallels] where handing this situation is discussed in detail.

Coordinated parallel observations involve adding a second instrument in parallel with existing primary observations as part of the same proposal.  Since the observations occur simultaneously, the two instruments will be pointing at different offset positions on the sky, depending on the instruments and modes selected (see JWST Field of View).

In this roadmap, you will be guided through the process of adding a coordinated parallel observation to a primary observation in APT.  This roadmap prompts you with questions or directs you to make choices and provides links to relevant JDox articles.  By policy, they must be scientifically justified; see NASA policy for coordinated parallels for more information.

Note: Using NIRCam WFSS or NIRISS Slitless spectroscopy (Grism) modes in parallel:  Specifying these modes in parallel is complicated by the need to take additional direct images before and/or after the parallel Grism exposures. This may require the addition of short "primary" exposures to handle the needed extra parallel exposure slots. If using one of these modes, see the worked example of handling this situation.



Specifying Coordinated Parallels

Here are questions and decision points to help you plan JWST coordinated parallel observations.

  1. What instrument pairing is needed for your science, and which instrument will be specified as “primary” and “parallel”?  Even if both instruments are equally important, one must be specified as the primary in the Astronomers Proposal Tool (APT).  
    Note: not all instrument pairings are allowed, and in some cases the primary and parallel instruments are not interchangeable.  
    Check the allowed pairings.

  2. Work with the Exposure Time Calculator (ETC) to understand the relative exposure times needed for both instrument configurations you want to use.  Select the instrument requiring longer exposures to be your primary instrument since your parallel instrument exposures need to fit within the primary exposure times. 

  3. Understand what you plan to do with dithering. Most imaging parallel modes have dither patterns that will work for both instruments.  These are selectable within the APT observing templates once your primary and secondary instruments are specified.  
    Note: Parallels with NIRSpec MOS prime must simply adopt the MOS dither or nod pattern.  See the APT coordinated parallel article where this is discussed.


  4. Enter the information for the primary instrument exposure specifications into the appropriate APT observing template.  If this is an imaging mosaic, you may want to verify mosaic details by using the  Aladin visualization tool.  
    Note: verify the schedulability of your primary observation with the APT Visit Planner and address any scheduling issues prior to adding your desired coordinated parallel specifications.

  5. Find and select the “Coordinated Parallel” checkbox in the APT observation template of your primary observation.  Then select the desired parallel instrument and mode from the pull-down menu.

  6. Open the parallel instrument tab in the observing template and fill out the exposure specifications for your parallel instrument.  There needs to be a one-to-one match between primary and parallel exposures.  Hint: hover the cursor over any red X’s in APT for help in resolving any errors reported.

  7. Once errors are resolved, run the Visit planner again to verify schedulability of the combined observations.


Go to the General Proposal Planning Workflow to complete the steps for proposal submission.




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