Caltech-Internal Target of Opportunity (ToO) Policy

Caltech Optical Observatories (COO) supports a Caltech-internal Target of Opportunity (ToO) program to enable its researchers to acquire data on unexpected, transient events by allowing interruption of regularly scheduled programs of Caltech observers at the Keck telescopes and the Palomar 200-inch telescope. In such cases, the observer at the telescope is obliged to set aside his or her program and make specific observations on behalf of the ToO researcher. The COO-internal ToO program for Keck supplements the WMKO partnership ToO program described in this PDF document. Note that WMKO partnership ToO interrupts have priority and override Caltech-internal interrupts that are scheduled but have not yet started observing. Furthermore, WMKO partnership interrupts may interrupt any observer without the restrictions described below.

Caltech-Internal ToO Program Policies:

  • Caltech-internal ToO projects are restricted to Caltech (and Northwestern — see below) researchers as designated by the appropriate selecting official.
  • Such projects must be among the applicant's highest priority requests for time on the telescope involved.
  • Caltech-internal ToO interrupts may be invoked only when a Caltech (or Northwestern — see below) observer is observing with the telescope. All Caltech observers shall support requested interrupts from authorized Caltech-Internal ToO program advocates; postdoc-led or small projects are no longer exempt from internal ToO program participation.
  • Caltech's collaborative agreement with Northwestern includes Northwestern participation in Caltech's internal ToO program on Keck Telescopes. Keck ToO requests from designated Northwestern ToO program advocates shall be supported by all Caltech observers, and Northwestern Keck observers shall similarly honor authorized Caltech ToO requests (up to negotiated program limits).
  • Each Caltech internal ToO interrupt is restricted to 1 hour of wall clock time. Subject to the limitations below, two Caltech internal ToO interrupts may be used to obtain 2 hours of wall clock time, per telescope per night. These two interrupts may be consecutive.
  • Caltech internal ToO interrupts may not normally be used to interrupt a telescope beyond 2 hours of wall clock time per night. For the Keck telescopes, time lost to WMKO Partnership interrupts are counted in the total. Thus, if a given Keck telescope experiences two 1-hour WMKO Partnership interrupts in a given night, additional interruption on that telescope using Caltech internal ToO interrupts will not be allowed.
  • Under extraordinary circumstances, e.g. detection of an important new type of transient or event, the interruption may exceed the 2 hour maximum. Both parties (ToO and regular observer) are expected to use their best judgement in such cases, and to report the details on any such extraordinary interruption to the COO Director.
  • The ToO observer is responsible for the execution of the ToO observations. The regularly scheduled observer may choose to perform the ToO observations at the request and on behalf of the ToO observer, in exchange for appropriate, mutually agreed compensation (e.g., co-authorship in any resulting publications).
  • Northwestern is allowed to use its Caltech internal ToO interrupts to "piggyback" on any WMKO Partnership ToO interrupt triggered by Caltech. In this mode, Northwestern is invoking the data sharing clause specified in the Caltech-Northwestern collaborative agreement, and no additional observing time is added beyond that obtained through the Caltech-triggered WMKO Partnership interrupt.
  • For regularly-scheduled Caltech observers, the time lost due to ToO interrupts will be tracked by COO (see reporting requirements, below). When this accumulated burden exceeds the lesser of 6 hours or 50% of the total allocated time, the COO Director will allocate Discretionary Time (DDT) as compensation. Compensation will typically be at a 2:1 rate but depends on availability of DDT and may take place in subsequent semesters.
  • ToO interrupt authorization is granted only for a specific semester; unused time assigned to a ToO program will not be carried forward to subsequent semesters.
  • All PIs who are allocated observing time will be given brief details of the successful ToO programs from previous years.
  • An interrupt may be activated only when the available equipment and moonlight conditions are consistent with the TAC recommendations. Seeing and photometric conditions are not a condition for any interrupt.
  • Caltech internal ToOs at Keck are activated following WMKO-established procedures. Interrupts on Keck telescopes shall be entered using the WMKO ToO Observing Request Tool (TORT). [The TORT tool is available through the Keck Observer Login Portal.] Palomar interrupts are activated by contacting the regularly-scheduled observer (e.g., by telephone or email).
  • In contrast to WMKO Partnership interrupts, instrument changes are currently not supported for Caltech internal ToO interrupts.
  • NEW for Semester 2024A: Similar to WMKO Partnership TOO policy, observers may request and be granted "uninterruptable" status for regularly-scheduled observations and thus be protected from TOO trigger interruption. Protected status is granted at the COO Director's discretion.
  • ToO reporting & data access requirements:
    • The scheduled observer shall send an e-mail to the ToO PI [copies to C. Martin (martinc [at] and A. Boden (bode [at]] immediately upon completion of the observing run, reporting on the time devoted to ToO observations and other relevant comments.
    • The observer shall deliver/make available the necessary data to the ToO PI.
    • Similarly, within 24 hours of an interrupt the ToO PI shall document in e-mail to A. Boden (bode [at] [copy to C. Martin (martinc [at]] reporting on the time used for each interrupt, with an account of the status of the ToO project.
    • Finally, the ToO PI shall also include a complete account of the status of his/her ToO projects, time invoked, etc as a part of the supporting material for subsequent observing proposals from this PI.

The log of active and past ToO projects, go to COO ToO Log.

Please share your feedback on this page at the COO Feedback portal

COO ToO Policy / v 0.5.2
Last updated: 26 September 2023 JXZ/AFB/RJB/ACM