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Changing Details of Approved Programs

It is recognised that some PIs may wish to modify observations after the ITAC-recommended queue and classical schedule has been approved by the Director. This might occur, for example, due to a change in scientific or technical priorities or a genuine mistake in the Phase I proposal (e.g. incorrect observing condition constraints).

Requests for change must be made by the PI to the Head of Science Operations for the relevant telescope (sleggett at, brodgers at and copied to the program's Gemini and National Gemini Office (NGO) contact scientists. Genuine or accidental differences between approved Phase I programs and the detailed Phase II observations may be also be identified by National Office or Gemini Observatory staff during verification. These too will be communicated to the Heads of Sci. Ops. and copied to the NGO.

If the change is "substantial", the Heads of Sci. Ops. will, at their discretion, contact the relevant ITAC member to seek a recommendation for approval or rejection of the change. Note that changes may affect other approved programs, by creating new duplicate observations or altering their likelihood of execution. Examples of substantial change include:

  • Changes in the science goals, e.g. due to new development in the area. A detailed justification should be submitted with the request.
  • Increases in the allocated time. Submit a detailed justification.
  • Change in to a different instrument or different instrument mode. Submit a detailed justification.


Smaller changes would not normally trigger communication with the ITAC member, but still require contacting the appropriate Head of Science Operations for assessment. Examples include:

  • Change of observing condition constraints (to better conditions, including any changes to airmass or hour angle constraints). Include a justification for the requested change.
  • Change of science target (to an identifiably different source). Submit target name, coordinates in J2000 (RA hh:mm:ss.s, DEC dd:mm:ss), and a brief justification with the request. The targets will be checked for conflicts with other programs.
  • Larger refinement of target coordinates (for the same source), when the adjusted coordinates trigger a warning from the OT. Submit target name, coordinates in J2000 (RA hh:mm:ss.s, DEC dd:mm:ss) with the request.


Changes that do not require approval:

  • Adjustment of integration time between observations within the same Science Program, such that the total used time remains within the allocation.
  • Refinement of observing technique such as changes in imaging filters, wavelength settings for spectroscopy, gratings and grism choices for spectroscopy. The Contact Scientist will inform the PI if it is judged that the changes are large enough to require approval from the Head of Sci.Ops.
  • Adjustments of target coordinates that do not trigger a warning from the OT, such as offsets and dither patterns.
  • Changes to observing conditions to the next worse bin, e.g. from IQ=70% to IQ=85%. These changes are typically chosen by PIs to increase the probability of obtaining data, if the PI determines that the science goals can still be met.
  • Requests to observe at the average parallactic angle for GMOS observations. However, PIs should ensure that correct information is included in the phaseII definition to enable the observations to be executed correctly.
  • Addition of, or changes to, calibration observations, including standard star observations.

Gemini Observatory will act on a request for change within seven days. Often the response time will be significantly shorter than 7 days. However, large lists of target changes or substantial changes in science goals may take up to 7 days for a decision. Requests for changes during a classical run can usually be accommodated if the PI notifies the Head of Science Operations of the need at least 7 days before the classical run begins. Final authority for resolving disputes over observation modifications rests with the Gemini Director.