The high-resolution spectrograph of the 6-m Large Azimuthal Telescope (BTA)

This paper presents the main parameters and design features of a cross-dispersed quartz diffraction spectrograph permanently mounted on one of the two Nasmyth-focus platforms of the 6-m Large Azimuthal Telescope (BTA). The Nasmyth Echelle Spectrograph is intended for the study of stars with high spectral resolution, R=60000. The spectrograph is equipped with various pre-slit devices (polarization analyzers, an iodine cell, etc.), and image slicers. An active-optics system that stabilizes the position of a star’s image on the entrance slit of the spectrograph to within about 0.1″ is mounted in the pre-slit part of the spectrograph. The optical layout of the Nasmyth Echelle Spectrograph is designed to obtain spectra without substantially reducing the spectral resolution in a wide wavelength range λ=300–1000nm. A unique mosaic composed of two echelle gratings is used as the main dispersive element of the spectrograph.