JWST Coordinated Parallels Roadmap

A step-by-step guide on adding coordinated parallel observations to an observing program for JWST is provided in this article.

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.

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, coordinated parallel observations must be scientifically justified; see NASA policy for coordinated parallels for more information.

Since coordinated parallel observing uses multiple instrument modes simultaneously, consider using the the "quick look" JWST Interactive Sensitivity Tool (JIST) to obtain a sense of the signal-to-noise and exposure time parameter space you may obtain with the same exposure time in both instrument modes you select.

Using the NIRISS WFSS (slitless grism) mode in parallel: specifying this mode in parallel is complicated by the need to take additional direct images before and/or after the parallel grism exposures. This requires 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 parallel observations

Words in bold are GUI menus/
panels or data software packages; 
bold italics are buttons in GUI
tools or package parameters.

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

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

  • 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. 

  • 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.  
    Parallel observations taken with NIRSpec MOS primary observations must adopt the MOS dither or nod pattern. Also, see the APT coordinated parallel article where this is discussed.

  • 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.  
    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.

  • 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 choices.

  • Open the parallel instrument's 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.

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

Go to the Getting Started with JWST Proposing to complete the steps for proposal submission.

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