JWST Target of Opportunity Observations

A target of opportunity (ToO), for JWST observations, refers to requested observations that are linked to an event, such as supernovae, that may occur at an unknown time. 

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See also: JWST Target of Opportunity Program ActivitationJWST Target of Opportunity Roadmap, Target of Opportunity Observations in the Call for Proposals material

A target for JWST observation is called a target of opportunity (ToO) if the observations are linked to an event that may occur at an unknown time. ToO targets include objects that can be identified in advance but which undergo unpredictable changes (e.g., specific dwarf novae), as well as objects that can only be identified in advance as a class (e.g., novae, supernovae, gamma ray bursts, tidal disruption flares, newly discovered comets, etc.). ToO proposals must present a detailed plan for the observations to be performed if the triggering event occurs.

To check on the observability of a ToO for JWST, consider using one of the JWST Target Visibility Tools. When a given ToO triggers, the proposer should quickly assess whether the target is visible and available for immediate observation by JWST and for how long the visibility window remains open if monitoring is required.  Also, the JWST Interactive Sensitivity Tool can be used to obtain a quick assessment of the S/N that can be achieved in a given exposure time.

What distinguishes ToOs from "time constrained" (or "time critical") observations, or potential director's discretionary time observations?

ToOs are generally not intended to be observations of periodic phenomena such as eclipsing binary stars, transiting planets, or Solar System objects. Observations of these types of objects are typically time constrained, and may be time critical if the observations must be done in a specified 24 hour window. For instance, if the objective is to observe a specified phase in the periodicity, lasting less than a day, then the observation is time critical. These types of observations are specified as regular fixed targets but with appropriate special requirements used to specify the timing requirements.  

At the other extreme are unexpected phenomena, for which no plausible proposal could have been submitted in the previous proposal cycle. These types of observations are typically more appropriate for director's discretionary time. However, there are other criteria, including the likely impact of scientific results, that must be considered with proposals for director's discretionary time.

Observing constraints for ToOs

The JWST project differentiates 3 levels of ToO, depending on the required turnaround time. These are called:

  • Non-disruptive ToO: A ToO for which the activation time is greater than 14 days
  • Disruptive ToO: A ToO for which the activation time is less than 14 days and greater than 3 days
  • Ultra-disruptive ToO: A ToO for which the activation time is less than than 3 days

The minimum turnaround time of 14 days for a non-disruptive ToO activation is because it is likely to be handled without significant impact to the scheduling process. Disruptive ToOs can be triggered with turnaround times of less than 14 days, provided all of the proposal details (except possibly the precise target position) are available in advance. Moreover, due to their scheduling impact, ultra-disruptive ToOs that require triggering within 3 days will incur an additional overhead 0.5 hours (30 minutes) per activation. Linked subsequent observations do not necessarily incur additional overheads, unless they are specified as time critical visits. 

 Because of the potentially significant effect that disruptive ToO and ultra-disruptive ToO observations can have on the JWST schedule, there will be a limited number of allowed activations of these categories in each cycle. The number of allocations will be provided each proposal cycle in the Call for Proposals.

Activating an approved target of opportunity program

Requesting activation

The Principal Investigator (PI) or designated alternate initiates activation of a Target of Opportunity (ToO) proposal by submitting an activation request, which are submitted by navigating to the JWST Program Information webpage, searching for the appropriate program, and selecting the Activate a Target of Opportunity link in the Request section of the program page. In the request the PI identifies which visit (or visits) to activate and supplies all the information needed to implement and schedule the observation. This information should include target position, instrument filter/grating combinations, exposure times, and any scheduling requirements not already included proposal.

Because there may be critical implementation questions, you must let STScI know where you can be reached 24 hours a day.

After submitting the request, the PI (or alternate) must contact their Program Coordinator (PC) and verify that the activation request has been received by the Institute. The PC verifies receipt of the activation request and discusses with the PI any remaining questions on observation and scheduling requirements.

Evaluation and implementation

STScI evaluates the effect of the ToO's interruption on the JWST schedule and how well the observations of this event meet the approved science goals. The STScI Director then makes the final decision whether to activate a ToO. The CS, the PC and Short Term Planning conduct a review of the proposal to assure the safety of the observations, to verify that the program complies with the observing time allocation and to identify execution opportunities.

Notable updates

  • Revised nomenclature for Cycle 2.

    Updated for 2020 Cycle 1.
Originally published