Hintze Centre for Astrophysical Surveys

Abstract:

Of the Gemini Multi-Object Spectrograph's (GMOS) scientific requirements, one which led to technically interesting areas was the ability to measure velocities to a accuracy of 2 km/s over the entire 5.5 arcminute square field. GMOS's design to meet this requirement includes a mechanical design for stiffness and without hysteresis or image rotation, and an open loop flexure control system which translates the detector position to compensate for flexure. The model used to predict the flexure is an empirical one developed from measured flexure results. In this paper we present the analysis of factors which enable meeting the 2 km/s requirement, and the observing strategies needed to make those observations. We look in particular detail at the development and test of that flexure compensation system, including both lab results and on-telescope results.

Abstract:

The Gemini Multiobject Spectrographs (GMOS) were designed to take advantage of the exquisite image quality expected of the Gemini telescopes. To achieve this, two of the many requirements placed on the optical system was that it not degrade the best image quality expected of the telescope by more than 10% while delivering a throughput of about 80% over the entire 0.4-1 μm waveband. In this paper, key components of the design and execution of this optical system are discussed and test results are presented demonstrating that it meets these requirements on Gemini today. Among other characteristics, we look at the image quality performance as a function of colour and field angle, the measured throughput, and the focalplane flatness on the detectors.