Conceptual design of the high-resolution optical spectrograph for the Gemini South Telescope

The high resolution optical spectrograph (HROS) for Gemini is currently within its conceptual design phase. The science requirements for this instrument demand spectral resolutions of 50,000 and 120,000 with entrance slits of 0.57 and 0.24 arcsec respectively. Amongst the current large telescope projects, HROS will be the only instrument of its class to be mounted at a Cassegrain station and this will pose considerable technical challenges which are described in this paper: HROS will be a spectrograph with unique characteristics, like prismatic cross-dispersion, immersed echelle grating and active compensation of flexure. HROS is expected to perform better than any other high resolution spectrograph with respect to throughput, resolution and simultaneous spectral coverage.