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Target of Opportunity Activation

Scheduling ToO Observations

Gemini North and South are accepting triggers for approved "Target of Opportunity" or ToO programs as described in the Call for Proposals. We recognize that many ToO programs require follow-up observations on various timescales. Every effort will be made to complete these observations but due to schedule (and weather) constraints this cannot be guaranteed.

Time Charging for ToO Programs

From Semester 2017A, Gemini is not carrying out detailed time balancing, per partner, from semester to semester. Observations executed on a ToO program are "charged" to the program in order to determine whether the program has remaining time, but any unused time at the end of the semester is lost. 

ToO Trigger Types:

  1. "Standard" triggers: observations that, once triggered, can be executed more than 24 hours in the future. This is essentially identical to the normal queue mode except that the targets are not known in advance. Thus, observations will be placed in the queue based on science rank and observing conditions constraints. If you want a triggered observation to be considered under this mode, you must complete the timing constraints in the Observing Conditions OT component. The PI will be notified if the telescope is not available within that time frame, and will be given the option to change his/her trigger.

  2. "Rapid response" triggers: observations that need to be done within the next 24 hours. The minimum response time is about 20 minutes and these triggers can interrupt ongoing observations, both classical and queue. Each semester only a few programs are allocated "Rapid Response" status by the ITAC. Details of this mechanism are given below. The Gemini North and South schedules show the science and engineering blocks available; the schedule is subject to change at short or no notice. Daily information about instrument availabilities and configuration can also be found on the North and South configuration pages. Please contact your program's Contact Scientist or the Instrument Scientist if you need more detailed information on the availability of the telescope during a specific period.

All types of ToO observations can be prepared and submitted using the standard sync operations of the Observing Tool (OT). It is also possible to trigger observations by sending a Uniform Resource Locator (URL) with all the observation information to secure web sockets on the observing database machines. Template observations in the programs are copied, populated with the target and guide star information, and then triggered.

Phase II Preparation

The basics of ToO Phase II preparation are the same as for regular queue programs. However, in this case the PI needs to define template observations that will be used once the targets are known. For programs with standard triggers that require a limited set of instrument modes, PIs should prepare templates similar to normal Phase II preparation. Programs that observe more transient objects (e.g. SNe, GRBs) often use many instrument modes so have to have more triggering options. For these programs the contact scientist will often copy a set of standard templates into the program. Please ask your contact scientist for additional instructions.

The template observations must be prepared by the regular Phase II deadline before each semester so that they can be properly checked. 

Template observations should be made for each instrument configuration that will be needed and should be stored in a folder called Templates. This template observations should include:

  • Science target acquistion (with matching PA and FPU-long slit or IFU-for the Science observation)
  • ToO type (only possible for programs with Rapid ToO status, see below)
  • Science target (dummy) <-- can leave as (0,0)
  • Guide star (dummy) <-- also could be left as (0,0)
  • Complete instrument configuration
  • Offset or instrument sequences as needed
  • Observes
  • interspersed GCAL flats and arcs as necessary

After being checked by NGO and Gemini staff, trigger template observations will have their status set to "On Hold" and the priorities set to the usual High, Medium, or Low. PIs should sync their programs and wait for the triggering event.

Each program has a ToO status based on the option ("None", "Standard", or "Rapid") approved during Phase I. The status is given at the main program level.

OT ToO status indication

The TOO status is also shown at the observation level for programs that are allowed to trigger TOO observations. Programs with Standard TOO status can only trigger Standard TOOs while programs with Rapid TOO status can trigger either kind.

Standard TOO program
Standard TOO observation

Rapid TOO program
Rapid TOO observation


Only one unique template for each configuration should be defined even if more than one observation with a given configuration may be triggered on a given night. If the URL-based triggering mechanism described below is not going to be used then an Observing Tool "Note" should be used to ask the Gemini contact scientist to make a number of copies of each template and leave them all at On Hold.

Triggering an Observation

Prepare observation

In most cases these steps are carried out using the Observing Tool. If URL-triggering is used then much of the preparation is done in software external to the OT that formats a URL string with all the required information. Scripts for automatically finding guide stars, formatting the URL, and submitting it are under development and the PIs for TOO programs can obtain them by contacting Bryan Miller (

  • Prepare a finding chart
  • Check Gemini North and South configuration web pages for available instruments and configurations
  • Sync program if not using the URL-based rapid response triggering
  • Select observation template(s)
    • The template(s) must have status "On hold"
    • If not using URL triggering
      • Copy the template(s) to a new folder. The new observations will have status "On hold".
      • Edit the new observations according to the guidelines below.
  • Update target component
    • Fill in target name and coordinates
    • Select guide star
  • Update instrument component
    • Exposure time
    • Central wavelength (if appropriate)
    • Position angle (if needed)
  • Update timing constraints if necessary. If no constraints are entered then Rapid ToOs will be given a 24 hour timing window.
  • Prepare note with extra details of the observation. For Rapid Response triggers the notes should include:
    • Time of slew (UT), either
      • Slew immediately
      • Slew when convenient within the next M minutes
      • Slew as close to HH:MM UT as possible
      • Slew within T hours after obsid [N] complete
    • Slew before time (UT) up until when the observation should be active
    • Designated contact information
      • Name of contact person
      • Phone number
      • Video IP (if available)
      • e-mail address
    • Acquisition information
    • URL of finding chart if not submitted as a File Attachment
    • Weather caveats and other information

Submit observation

  • OT triggering
    • Change the status of the observations to be triggered from "On hold" to "Prepared."
    • Sync the program to the Gemini database.
  • URL triggering
    • The PI software sends the URL string to the appropriate web socket.

Data Collection and Packaging

For Standard triggers the observations will be scheduled at the appropriate time in the queue. For Rapid Response triggers, the observers are notified of the triggers immediately and respond according to the timing instructions given. If the observers have any questions about the observtion then they may get clarification from the PI contact given in the note. If the observation cannot be done then the reasons will be added to the note.

Raw data files usually arrive at the Gemini Observatory Archive within a few minutes of being taken and are accessible by the PIs. For Rapid Response programs the observer will send an e-mail to the PI contact announcing that data is available.