Design of an echelle spectrograph without knobs

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Session 10 -- Remote Observing, Ground-Based Telescopes and Instruments
Display presentation, Monday, 9, 1995, 9:20am - 6:30pm

[10.08] Design of an echelle spectrograph without knobs

P. Ryan, J.R.P. Angel (Steward Observatory)

We present designs for echelle spectrographs for 6.5 m telescopes. While generally along the lines of Vogt's HIRES at the Nasmyth focus of the Keck I telescope, we incorporate fused silica prism cross dispersion for higher transmission, and use cameras that record simultaneously full 300 - 1100 nm wavelength range of CCD detectors. Six detectors are placed tangent to the focal sphere of a Schmidt camera. Each has its own thin field flattener. In this way excellent image quality is maintained while the obscuration by the detector array is minimal, even though it is big enough to cover the entire cross dispersed spectrum. Each back-illuminated CCD is dedicated to a limited spectral range, and can be given appropriately optimized coatings for highest efficiency. Designs for 20 and 30 cm beams have been produced, both using 60 cm Schmidt plates and achieve resolving power slit width products of 50,000 arcsec. The 2048 square CCDs yield spectral resolution sampling of 200,000/pixel. The "point and shoot" character of the spectrograph should result in simplified controls and software.

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