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Time Allocation Committees (TAC) processes

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Gemini Time Allocation proceeds in two phases, outlined here. Important dates for the upcoming semester are given in each Call for Proposals. This page describes the National and International Time Allocation Committee (TAC) process.

After the Call for Proposals deadline at the end of March or September, each National Gemini Office (NGO) collects the proposals from its community, resolves logistical issues and errors, and evaluates them for technical feasibility. Each Participant then peer reviews its proposals via a National TAC (NTAC), and creates a ranked list based primarily on scientific merit, but also on strategic feasibility. NTAC meetings generally occur 4-6 weeks after the proposal deadline (late Oct/early Nov or late April/early May).

The outcomes of the NTAC meetings are ranked lists of approved programs and recommended time allocations to fill each Participant's time allocation, for consideration by the International TAC (ITAC). These approved programs are forwarded to Gemini via an NTAC package, due ~6 weeks after the proposal deadline each semester (generally 10-13 May or 10-13 November). 

The Gemini International TAC merges the proposals to create a single combined list of programs for execution. The ITAC only sees those proposals that are forwarded by each NTAC. Prior to the ITAC meeting in the third or fourth week of May or November, the ITAC chair merges all of the forwarded programs from each Participant to produce a draft queue. The merging process is a deterministic process that steps through each Participant's ranked program listing and distributes the time according to each Participant's share of the total time. The draft queue is shared with the ITAC members and with the Gemini Heads of Science Operations who construct a preliminary telescope schedule (incorporating engineering and commissioning work with classical time requests and other considerations) and communicate any issues or concerns for operations.

During the ITAC meeting, the ITAC representatives analyze the draft queue in detail; they consider instrument availability, Target of Opportunity (ToO) programs, duplicate observations and the distribution of programs across different observing condition constraints, and adjust the ensemble of proposals to construct the best "queue", both for the individual communities and for the observatory. Duplicate observations are defined as observations of the same target with the same instrument configuration.  When such conflicts arise, the higher ranked program retains the observation and the target is removed from the lower ranked program. The PI of the lower ranked program may replace the target with an alternative. 

The outcome of the ITAC meeting is a recommended queue list (including scientific ranking bands), and classical program list for execution in the coming semester. This recommendation is forwarded to the Gemini Director for detailed consideration. The final allocation is at the Director's discretion and changes can be made, although these are generally minor in nature. The final approved list of programs is shared with the NGOs and ITAC members, and "NGO feedback" is generated which includes relevant comments intended for the Principal Investigators for proposals that were forwarded to ITAC.

Within a few days of sending the NGO feedback, the observatory notifies all successful PIs directly by email with information about their time allocation and how to start the Phase II process. At the same time, all the approved programs are published on the Gemini website and the "Phase II skeletons" are made available in the Observing Database. This generally occurs around 15 June or 15 December.

Time Allocation Committees (TAC) processes | Gemini Observatory


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