JWST Target of Opportunity Observations

A target for JWST observations is called a target of opportunity (ToO) if the requested observations are linked to an event that may occur at an unknown time. ToO observations must be called out and triggering conditions described in your proposal.

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Main article: JWST Target of Opportunity Program Activitation

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 Target Visibility Tools. When a given ToO triggers, the user can 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.

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 minimum turn-around time for non-disruptive ToO activation, without significant impact to the schedule, is 14 days. 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. However, because of the significant effect disruptive ToO observations potentially can have on the JWST schedule, there will be a limited number of disruptive activations allowed in each cycle. Moreover, due to their scheduling impact, 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. 

Each cycle will have a limited number of disruptive ToO activations to allocate, based on an expectation of how many interrupts the scheduling can absorb. The number of allocations will be provided in the appropriate Call for Proposals.

Activating an approved target of opportunity program

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