This page provides best estimates, at the time of the Call for Proposals, of instrument restrictions and target (RA, DEC) accessibility for 2023B.

All instruments are restricted for sky visibility as described in the Table below. In addition:

• A brief engineering shutdown is planned for Oct 30 - Nov 03, 2023.
• Observations using the Gemini North laser guide star (LGS) system are restricted to greater than 40 degrees elevation. How this translates into RA and DEC restrictions is indicated in the below Table.
• Altair NGS and LGS+P1 (super-seeing) modes are fully functional. However, there is currently a technical issue with LGS mode, a resolution for which is being worked on, and this could potentially impact the availability of GN LGS in the 2023B semester.
• MAROON-X, NIFS and NIRI may share the bottom port of the telescope and will be block scheduled. NIRI will not be offered for new proposals in semester 23B. We expect that the other two instruments will be scheduled for approximately month-long observing blocks. This pressure means instruments may not be scheduled during the semester, or may be scheduled for limited periods of time. Investigators with time-critical observations using NIFS or MAROON-X should specify both ideal dates and frequency for their observations, as well as less-preferred dates or sampling frequency.

^**Due to limited sky availability during the semester, GMOS MOS programs requiring pre-imaging should not have targets in this region, and other programs with targets in this region should not require a large amount of time, or have strict timing or observing constraints.

All instruments are restricted for sky visibility as described in the Table below. In addition:

• An engineering shutdown is planned for Sep 25 - Oct 24, 2023, in order to execute the delayed primary mirror coating at Gemini South. These dates are provisional, and may change based on the progress of the coating preparations. These nights will not be available for time critical events. The time available at RAs between 20 hours and 6 hours will be reduced by 20% to 30% and so investigators with targets in this range are advised to have alternative targets available.
• GMOS South is expected to be available with a replaced detector from June 2023 onwards, but prospective PIs should check the instrument web pages for updates on availability.
• Observations using GeMS are restricted to greater than 45 degrees elevation. How this translates into RA and DEC restrictions is indicated in the below Table.
• Zorro and IGRINS will be available in Semester 2023B.  Scheduling of these instruments will be driven by the demand.

^**Due to limited sky availability during the semester, GMOS MOS programs requiring pre-imaging should not have targets in this region, and other programs with targets in this region should not require a large amount of time, or have strict timing or observing constraints.

At each Gemini telescope, instruments are mounted at the Cassegrain focus on the instrument support structure (ISS). A science fold mirror mounted inside the ISS can be rotated to send the light from the telescope to any of four side-looking ports, or can be retracted so that the light goes to the up-looking port. At each site, the calibration unit and the Adaptive Optics system use two of the side ports, leaving two side-looking and one up-looking port for other instrumentation. As more than three instruments are offered each semester, instrument swaps are required and not all instruments will be available for the entire semester. Instrument swaps are driven by demand and scheduled to minimize impact on the queue. Certain targets or entire programs may not be feasible once the final schedule is determined, at ITAC or thereafter. If an instrument is requested for less than 6% of the Bands 1+2 time, the Observatory reserves the right to limit the RA range available to programs, or to not schedule the instrument.

Non-sidereal targets can have a broader range in RA than indicated in the Tables above due to, for example, the need to observe comets relatively close to the Sun. The ephemeris for any submitted target however must include a position that is accessible between evening and morning twilight at some point in the semester. For rapidly moving targets PIs should specify in the proposal when the target is accessible, and the coordinates of the target at that time, so that the observation can be checked for feasibility.

Gemini Observatory attempts to schedule all time-critical observations whenever possible within the constraints imposed by instrument availability, instrument configuration, weather, and science ranking band. Additionally, nights not scheduled for multi-instrument queue including classical and other observing modes, shutdowns, commissioning, etc., impose additional constraints on time-critical programs. Short observations (~1 hour) can often be accommodated during priority visitor periods. Programs with time-critical observations are asked to include detailed scheduling constraints with their proposal, such that they can be considered along with other constraints when developing the telescope schedule each semester.