This page describes the various types of observations that JWST proposers can request, including observations of targets of opportunity, of Solar system moving targets, of targets that have not yet been discovered or identified, follow-up observations of JWST pre-imaging, time constrained observations, coordinated parallel observations and pure parallel observations. 

Primary observations are classically targeted observations that determine the telescope pointing, orientation, and scheduling. There are other types of observations that require additional considerations in planning and scheduling. These include target of opportunity observations (disruptive or non-disruptive), observations of Solar System targets, observations of targets that have not yet been discovered or identified, follow-up of targets from JWST pre-imaging, time constrained or critical observations, and parallel observations (coordinated or as pure parallel). 

Many of these observation types are described with examples in Methods and Roadmaps.

In general, observing programs that require the use of special requirements, especially those that affect timing and schedulability of observations, must include a scientific justification of why the Special Requirements are necessary.

Primary observations

Target of Opportunity (ToO) Observations

A target for JWST observation is deemed a Target of Opportunity (ToO) if it is associated with an event that may occur at an unknown time. ToOs are distinct from time constrained observations.

ToO targets include objects that can be identified in advance, but which undergo unpredictable changes (e.g., some dwarf novae), as well as objects that can only be identified in advance by class (e.g., novae, supernovae, gamma ray bursts, newly discovered comets, etc.). ToOs are generally not suitable for observations of periodic phenomena (e.g., eclipsing binary stars, transiting planets, etc.). ToO proposals must provide a clear definition of the trigger criteria and present a detailed plan for the observations to be performed in the "Technical Justification" of the PDF attachment if the triggering event occurs. A ToO activation may consist of a single observation or of a set of observations executed with a pre-specified cadence. The number of ToO activations per observation must be indicated in the APT Proposal information form (using the expandable menu of the same name); for more information, see JWST Filling Out the APT Proposal Form.

ToO response times are specified in the APT Special Requirements. The minimum turn-around time for activation defines whether a ToO is Non-disruptive, Disruptive, or Ultra-disruptive. Triggering or activation times are measured from the time when the activation request is submitted to start of the first observation. Due to their significant impact on the JWST schedule, the number of Disruptive and Ultra-disruptive activations are restricted in each cycle. Some proposal types and modes are excluded from ToO observations, as described below.

†This number includes any Ultra-disruptive ToOs.

*This is the maximum totaled over all accepted programs, not the maximum that can be requested in any given proposal.

Information on activating an approved target of opportunity program is in JWST Target of Opportunity Program Activation.

Please see the ToO Proposals section of JWST Proposal Categories for additional information.

Carry-over ToOs

Standard ToO proposals terminate at the end of each cycle. Proposers may apply for "carry-over" status if the target phenomena have a low probability of occurrence during one cycle. The proposal needs to include an estimate of the likely probability of occurrence in Cycle 5 (i.e., an annual probability).  Carry-over ToOs will remain active through the subsequent cycle and will terminate at the close of that cycle. The request for carry-over status must be made when the proposal is submitted. There is no mechanism for requesting an extension during the cycle. Carry-over ToOs are allowed for both disruptive and non-disruptive observations.  

Requests for Carry-Over status should be justified in the APT Special Requirements.

Future Cycles ToOs

As with other GO categories, non-disruptive ToO proposals can request triggers in up to 2 future cycles (i.e. in cycles N, N+1 and N+2), or in up to 4 future cycles (i.e., in cycle N, N+1, ... N+4) under the Long-Term Monitoring Initiative. Disruptive ToO proposals are restricted to the current cycle. Future Cycle ToOs are not eligible for carry-over status. If a ToO is not triggered in Cycle N, then that time will be dropped from the program. GO programs should only request time in future cycles if they are specifically for objects triggered in that cycle, and not if they are associated with follow-up observations for an object triggered in a prior cycle.

Requests for Future Cycle time should be justified in the APT Special Requirements.

The APT Proposal Information form should indicate the number of ToO activations per observation (using the expandable menu) for each cycle under consideration. Proposers should use the "Future Cycle" drop-down menu to enter the future cycle time and use the "Request custom time allocation" to override the APT calculated allocation for the current cycle. For more information, see JWST Filling Out the APT Proposal Form.

Please see the Future Cycles GO Proposals section of JWST Proposal Categories for additional information.

Duplications

In the case of duplications, triggers from previous-cycle ToOs  have priority over current-cycle ToOs. Before applying for ToO observations, proposers must identify and discuss duplications with approved past-cycle carry-over programs or approved Future Cycles ToO programs.

Solar System targets

JWST can observe most targets within our Solar System, although there are a few exceptions. The Sun, Earth, Mercury, Venus, and the Moon cannot be observed due to the orientation of JWST's sunshade. As moving targets, Solar System targets may have reduced periods of visibility as compared to fixed targets. In Cycle 5, the rate of motion for moving targets may not exceed 75 milliarcseconds per second. Proposers should consult the JDox Moving Target Field of Regard, JWST Moving Target Observations, and the JWST Moving Target Visibility Tool pages for additional information in planning this type of observation. Proposers must ensure that an ephemeris of sufficient accuracy is available for the appropriate epoch; observations that prove infeasible for technical reasons will be disallowed.

NIRSpec MSA-based observations of moving targets may only be proposed using the MOS Longslit observing method with the Wide Aperture Target Acquisition or Verify Only TA options. MSA-based Target Acquisition (MSATA) is not possible on moving targets. 

It is now possible to execute "shadow" observations for moving targets; see JWST Moving Target Acquisition and Tracking for more information.

Users will be able to visualize the track of a moving target over short periods of time against a sky image using the Aladin visualizer tool in APT.

Observations of targets that have not yet been discovered or identified

Investigators may wish to propose for JWST observations of targets that have not yet been discovered or identified. With the exception of NIRSpec MOS observations that require pre-imaging (see Follow-up Observations of JWST Pre-imaging), such proposals are generally allowed only if there is a certain time-criticality to the observations, where proposing for the same observations in the next regular review cycle (after the target has been discovered) would be impossible or would make the observations more difficult (e.g., the object fades rapidly, or its temporal behavior is important), or would lead to diminished scientific returns. Those criteria are generally satisfied for GO observations of ToO targets, and there may also be other circumstances in which proposals for such targets are justified. However, in the absence of demonstrated time-criticality, observations will generally not be approved for targets that have not yet been discovered or identified. Examples of targets that are not suitable for this type of proposal include color-selected galaxies, transiting exoplanets, or stars newly discovered in the course of an ongoing survey.

Follow-up observations of JWST pre-imaging

Same-cycle follow-up spectroscopic observations of sources identified through JWST NIRCam imaging programs are permitted. For example, a proposal may request imaging with NIRCam as a means of identifying a specific type of target (e.g., high redshift galaxies) for subsequent spectroscopy with NIRSpec. The proposal must include the imaging observation defined in APT, and specify the expected number density and magnitude distribution in the anticipated discovery of new targets. 

Proposers should be aware of the minimum timeline for pre-imaging, and other restrictions, detailed in NIRSpec MOS and MSATA Observing Process and NIRSpec MOS Operations - Pre-Imaging Using NIRCam.

Time constrained observations

Time constrained observations with JWST are observations required to begin within a specified date and time interval, or specified phase for sources with known periods. They constrain the JWST schedule to an extent dependent on the length of the window for the start time.

Time critical observations are those required to start within a constrained window that is less than 1 hour. Due to their impact on the schedule, time critical observations will incur an additional overhead of 1 hour per visit. Observations with execution windows greater than or equal to 1 hour are not considered to have a significant impact on the scheduling, and therefore do not incur any additional overheads. See JWST Observing Overheads and Time Accounting Overview for a description of accounting, including Smart Accounting, and overhead terms.

There are several kinds of time constrained observations that could be considered time critical in some way. Some scientific examples might include observations of specific phases of variable stars, many transiting exoplanet observations, and some Solar System observations. Observations that require a particular telescope orientation (or position angle) are implicitly time constrained; annual visibilities at a specific orientation can be limited to 10 days or less. The JWST Target Visibility Tools and/or JWST Moving Target Visibility Tools may be useful in determining these time constraints on a fixed orientation at a given date of observation.  

Coordinated JWST observations with other observatories are by definition time constrained observations, which may or may not be time critical. Linked subsequent observations (specified using the SEQUENCE OBSERVATIONS NON-INTERRUPTIBLE timing special requirement in APT) do not necessarily incur additional overheads, unless they are also specified as time critical visits with critical scheduling windows. Linked observations that are scheduled to occur within 4 hours of a previous observation will be considered time critical observations, incurring the additional overhead. Proposers can only request SEQ NON-INT with a clear scientific justification. Unjustified requests will not be permitted. 

Proposals may request time constrained observations for a specific date or range of specific dates, when scientifically justified, and can be specified in APT with Timing Special Requirements. See JWST Time-Series Observations for planning monitoring sequences. All time constraints should be justified in APT and in the "Special Requirements" section of the PDF attachment. 

Parallel observations

Parallel observing refers to simultaneously operating more than a single science instrument (limited to two instruments for Cycle 5). For JWST proposals, there are two basic modes of parallel operations: coordinated parallels and pure parallels. Further information with examples, roadmaps, and templates are provided on JWST Parallel Observations. Related policy can be found on JWST Science Parallel Observation Policies and Guidelines.

Coordinated parallel observations

Coordinated parallel observations are those in which simultaneous observations are made with an instrument other than the primary instrument. In past cycles, the science goals for the parallels were required to align closely with the prime science program; starting this cycle, coordinated observations may be proposed to advance goals that complement or enhance the prime science. Coordinated parallel observations must be explicitly justified in the proposal. In Cycle 5, the following coordinated parallel modes will be supported:

• NIRCam WFSS prime: MIRI imaging or NIRISS imaging as parallels
• NIRCam imaging prime: MIRI imaging, NIRISS imaging, or NIRISS WFSS as parallels
• MIRI imaging prime: NIRCam imaging or NIRISS WFSS as parallels
• NIRISS WFSS prime: MIRI imaging or NIRCam imaging as parallels
• NIRSpec MOS prime: MIRI imaging or NIRCam imaging as parallels
• NIRSpec IFU prime: NIRCam imaging as parallel.

NIRISS WFSS with NIRCAM WFSS is not supported as a coordinated parallel; however that combination is possible as a pure parallel (see below). Only direct imaging with standard narrow, medium, or broad band filters is allowed for NIRCam and MIRI observations in these coordinated parallel modes. Additional instrument combinations may be available in future cycles.

Pure parallel observations

Pure parallel observations utilize instruments other than the primary instrument on observations from unrelated proposals. Unlike coordinated parallels, pure parallel observations are proposed as entirely separate programs of investigation. Pure parallels use parallel observing slots created by observations of programs that do not use coordinated parallels. Pure parallel observations will not be allowed to influence the dither patterns or other aspects of the observing strategy of the primary observations to which they are attached, since the primary observations will belong to entirely separate science proposals.

Pure parallel programs may propose for observations with NIRCam imaging, NIRCam WFSS, NIRISS imaging, NIRISS WFSS, and MIRI imaging. NIRSpec and MIRI WFSS are not allowed as the parallel instrument. For accepted programs, the observations will be paired with suitable prime observations from other programs. Some prime templates cannot have pure parallels attached to them, including MIRI Coronagraphic Imaging, NIRCam Coronagraphic Imaging, NIRCam Time Series, NIRCam Grism Time Series, NIRISS Single Object Slitless Spectroscopy, NIRISS Aperture Masking Interferometry, and NIRSpec Bright Object Time Series. Please check JWST Parallel Observations for the full list of pure parallel template combinations that are allowed and expected to be available for use in Cycle 5. For pure parallels, only a single exposure specification is allowed per observation. 

The number and characteristics of pure parallel exposure opportunities (slots) will not be known until Cycle 5 selection is complete, but slot data from previous cycles provide a useful reference. For example, an average of 350 prime visits per cycle allowed at least two parallel optical configurations per visit and at least 1500 seconds of parallel exposure time per configuration, yielding up to 1400 hours of total exposure time. See the Pure Parallels FAQ section of the JWST Parallel Observations page for more details. Proposers are strongly encouraged to use the jwst-pure-parallel package to assess whether their specific observing scenario would have been viable in previous cycles.

Pure parallel programs cannot include a ToO component. Proposers are free to submit DD programs to follow up on any transients that are detected (note though that the response time will be slower than for a ToO).

Please see the Pure Parallel Proposals section of JWST Proposal Categories for additional information.

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