THuCIDIDES: a high-efficiency multimode spectrograph design for the Hale Telescope

This paper describes the operating parameters and initial design of a new spectrograph proposed for the 200-inch Bale Telescope at Palomar Observatory. The instrument, whose working name is THuCIDIDES (Two Hundred-inch Cassegrain Image-Deblurred Interchangable-Disperser/Echelle Spectrograph), will feature high system efficiency and multiple modes of operation, including low- and intermediate-resolution long slit and mufti-slit capability over 12.5 x 3 arcmin fields, and a cross-dispersed echelle mode covering 3800-8500 Angstrom at R = 20000 (with a 1.2 arcsecond slit) up to R = 60000 (with an image slicer). A 4096 x 4096 pixel CCD will serve as the detector. The quasi-Littrow echelle configuration and use of a prism cross-disperser will result in high system efficiency, estimated at similar or equal to 14%. The compact design will permit mounting in the Cassegrain ring plane, to reduce susceptibility to flexure. An optional fast-guiding tilt mirror provides modest improvement to seeing FWHM and slit throughput.