Instrument Overview and Observing Modes:

GMOS (Gemini Multi-Object Spectrographs) North and South are the medium-resolution optical spectrographs at Gemini. Long-slit, multi-object, and integral field unit spectroscopy modes are offered, as well as imaging with narrow/broad band filters. The Gemini GMOS page provides a comprehensive overview including references to the design. The North and South detectors consist of three 2k x 4k pixel CCDs each. The plate scale is roughly 0.08 arcsecond per pixel. Additional information on GMOS can be found in the GMOS Cookbook.

  • Red-Sensitive CCDs manufactured by Hamamatsu Photonics were installed at GMOS-S in June 2014 and at GMOS-N in February 2017; additional information regarding these CCDs is available on the GMOS Detector Array webpages.
  • The multi-object spectroscopy (MOS) mode requires the use of a dedicated software provided by the observatory. Follow this link for the current GMMPS MOS mask software and documentation.
  • Important: Before reducing GMOS data, you should check its Status and Availability webpage for information and warnings that can affect your data.

Data Reduction:

Proposal Preparation:

Planning observations for GMOS can be challenging because of the large number of available instrument configurations and observing modes. Try our new GMOS Observation Planning Guide. This document contains guides to instrument configuration and baseline calibrations, as well as Phase 1 and Phase 2 checklists.

Frequently Asked Questions:

Some questions and their solutions can be found on the FAQ page. Many of these are helpdesk questions that have been previously submitted and answered.

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Last updated or reviewed September 28, 2020.