APT Pure Parallel Observations

Pure parallel science observations are proposed and implemented differently in JWST APT from regular observations and from coordinated parallel observations.

On this page

See also: JWST Parallel Observations for an overview and templates allowing pure parallel attachments.

Pure parallel observations form entirely separate programs from the primary science observations they will be attached to, and hence involve a separate APT proposal. Pure parallel programs will use observing slots created by approved "regular" proposals that will be identified for possible use with pure parallel observing. However, due to the nature of these proposals, the details cannot be known at the time of initial submission.

For pure parallel proposing, you will not specify targets initially but rather enter some number of realistic placeholder observations into APT to indicate the kinds of pure parallel exposures that are needed for your proposed science. You must decide what kind of slots and pointing constraints will accommodate your science goals and the number of slots needed to accomplish the science you propose, and you will need to specify a reasonable estimate of the exposure specifications and total amount of observing resources that will be used if the proposal is accepted (see below). This information is needed so that you (and the TAC) will have an assessment of the total potential impact of the proposal, should it be approved. Details must be provided in your science justification, which will be attached to your APT file prior to submission (as with other programs).

After acceptance, and when the available pure parallel slots are known, you will develop a detailed APT proposal and attach proposed observations to actual parallel slots. This process is described in more detail below.

Pure parallel observing will be made available to Cycle 3 proposers on a shared risk basis. Development is still ongoing to support a full implementation in the scheduling system.

As with coordinated parallels, pure parallel exposures nominally hide completely under the primary exposures to which they attach. However, because of the way the onboard scripts operate, the script compile times and mechanism moves must be done serially for the primary and parallel exposures. Hence, it is recognized that adding pure parallel exposures will have some modest impact on the resources accounted to the primary program. The magnitude of this impact is not modeled in the APT accounting process, and this impact will not in actuality be accounted against the primary proposal.

Proposing for pure parallels

See also: JWST Call for Proposals for Cycle 3

Proposers must decide what kind of parallel observations (observing mode, filters and/or grisms, minimum exposure times needed, etc.) will accommodate their proposed science, and how many such observations would be needed. (If appropriate, a range in the number of observations that would be acceptable may be given.) Furthermore, pure parallel proposers will have to specify any other restrictions on the desired slots to which their parallel observations are to be attached (e.g., allowed ranges of Galactic or ecliptic latitude). These details must be described in the "Description of the Observations" section of the science PDF proposal attached to APT prior to submission. Pure parallel observations are not allowed to place timing or position angle constraints on the proposed observations.

How to use APT to prepare a pure parallel proposal

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

After opening a new JWST APT proposal, select the Pure Parallel Program check box on the Proposal Information page, which designates the APT file as being a pure parallel proposal. This removes the Targets section of the APT file; a value of PARALLEL is entered automatically into the Target field of your observation templates. The proposer should fill out one or more observing templates in APT (one typical example for each observing mode being requested) to indicate the relevant parameters of the exposures being requested. Details on how to fill out the relevant APT templates and estimate the observing resources being requested are given below

The "normal" proposal accounting numbers produced by APT will not be meaningful for pure parallel proposals and can be ignored, but an alternate method of calculating an estimated resource time to enter into the APT Proposal Information form must be provided. See the information below for details.

After a pure parallel program is accepted

After acceptance of a pure parallel program, actual observing slots must be assigned to your observations. The accepted pure parallel program will need to be reviewed to compile the list of exposure specifications.  These specifications will determine the observing slots that will be distributed to the pure parallel program.  Depending on the number of pure parallel proposals accepted and the severity of the competition for available slots, STScI may convene the accepted PIs of pure parallel programs into a negotiation process to assign the slots. Once the slots are assigned, each PI will need to prepare an APT proposal specifying the actual observational details for each slot and submit it for use in scheduling. This needs to happen as soon as feasible after acceptance because the details are needed to construct a valid long range plan, which drives the scheduling process for each new observing cycle. STScI will contact accepted proposal PIs with the details and schedule.

Filling out APT forms for pure parallel proposals

  1. In the Proposal Information section, check box Pure Parallel Proposal

  2. In the Observations section, click on New Observation Folder.

  3. Create one observation for each type of observation and exposure required to execute the proposed pure parallel science. In this context, "type of observation and exposure" means a combination of instrument, observing mode, optical element selection (filter[s] or grism), and minimum exposure duration. Note that if more than one exposure setup is proposed to be obtained at a given position on the sky (e.g., imaging with more than one filter per filter wheel, or WFSS observations with a grism as well as direct images), one observation needs to be created for each of those exposure setups. This is different from regular observation template specifications where multiple filters could just be listed sequentially within a given instance of the observation template.

  4. For each of the observations specified, fill out the exposure specifics. This is done as follows for the observing modes available for pure parallel observations:

    1. For the NIRCam imaging template (Instrument = NIRCam, Template = NIRCam Imaging):
      1. Select desired Module and Subarray
      2. Select desired Short Filter, Long Filter, Readout Pattern, Groups/Int, and Integrations/Exp
      3. See the Duration for Science box above the exposure specification area. Note down this value for the observation.

    2. For the NIRCam WFSS template (Instrument = NIRCam, Template = NIRCam Wide Field Slitless Spectroscopy):
      1. Select desired Module (Subarray = FULL is already pre-selected)
      2. In the Exposure panel, select Mode (DIRECT, GRISMC, or GRISMR). Note that for NIRCam WFSS pure parallel proposals, one of the observations needs to specify a direct image exposure. One direct imaging observation needs to be created for each long filter used in the proposal.  When DIRECT mode is selected, an associated panel called GRISM Observations appears that lists all observations in the proposal where Mode = GRISMC or GRISMR. Check all grism observations that should be associated with the DIRECT image in this observation. These associations should each have the same long wavelength filter; mismatching long wavelength filters between a DIRECT image and a GRISM observation will generate an APT error. It's recommended that users create both GRISMC and GRISMR observations for each DIRECT image to mitigate spectral overlap. 
      3. Select desired Short Filter, Long Filter, Readout Pattern, Groups/Int, and Integrations/Exp
      4. See the Duration for Science box above the exposure specification area. Note down this value for the observation.

    3. For the MIRI imaging template (Instrument = MIRI, Template = MIRI Imaging):
      1. Select desired Subarray
      2. Select desired Filter, Readout Pattern, Groups/Int, and Integrations/Exp
      3. See the Duration for Science box above the exposure specification area. Note down this value for the observation.

    4. For the NIRISS imaging template (Instrument = NIRISS, Template = NIRISS Imaging):
      1. Select Subarray = FULL
      2. Select desired Filter, Readout Pattern, Groups/Int, and Integrations/Exp
      3. See the Duration for Science box above the exposure specification area. Note down this value for the observation.

    5. For the NIRISS WFSS template (Instrument = NIRISS, Template = NIRISS Wide Field Slitless Spectroscopy):
      1. Select Mode (DIRECT, GR150C, or GR150R). Note that for NIRISS WFSS pure parallel proposals, one of the observations needs to specify a direct image exposure. (To direct the user in this respect, the Mode is defaulted to DIRECT.) For Cycle 3, we recommend that one direct imaging observation be created for each filter used in the proposal.
      2. Select desired Filter, Readout Pattern, Groups/Int, and Integrations/Exp
      3. See the Duration for Science box above the exposure specification area. Note down this value for the observation.

  5. For each of the observations created as described above, evaluate how many distinct pointings (meaning distinct targets of the primary observations, i.e., ignoring dithers) will be required at a minimum to fulfill the science goals laid out in the proposal. Make sure these numbers are mentioned and justified in the "Description of Observations" section of the proposal PDF attachment.

  6. Calculate the grand total duration of the pure parallel observations proposed. Calling the durations of the m different observations "Duri" and the associated minimum number of pointings for each observation "Ni", this grand total duration is equal to the following: \Sigma_{i = 0}^{m} {\it N}_i {\it Dur}_i

  7. In the Proposal Information section in APT, click on Request custom time allocation button.  

  8. In the Requested Time field that shows up, enter the grand total duration value calculated in the previous step. Make sure you choose the correct time unit (which is currently defaulted at Days). You can ignore the accounting numbers produced by APT automatically, as they are not relevant for pure parallel proposals.

  9. In the Time Req Explanation field, enter the following: "Pure Parallel proposal. Allocation value entered following prescription given in the 'JWST APT Pure Parallel Observations' article."

Status of pure parallel proposals

To view the current and previous cycles operational matches for JWST pure parallel programs, please see https://parallels.stsci.edu/

Latest updates
    Minor updates under filling out APT forms for pure parallels

    Updated description on how to read exposure timing values as of APT 2020.2 release.

  • Minor updates in preparation for Cycle 1.

    Updated for APT 27.1 release

    Changes made for consistency with current Cycle 1 expectations for pure parallel support.

Originally published