A high resolution fibre-fed echelle spectrograph for the Southern African Large Telescope

摘要

The design of the Canterbury Extremely Large Echelle Spectrograph on the Telescope In Africa (CELESTIA) is currently in progress. This high-resolution fibre-fed echelle spectrograph will be used with the Southern African Large Telescope (SALT) which is currently under construction at the South African Astronomical Observatory, near Sutherland, South Africa. CELESTIA uses a mechanically aligned mosaic of two 304 x 408-mm echelle gratings, and cross-dispersion is achieved using two large prisms in double-pass. An extremely fast (f/0.65 in white light, f/2.2 in monochromatic light) camera with all-spherical surfaces based on the design of Epps and Vogt for Keck HIRES has been adapted for this spectrograph. The dispersive elements of CELESTIA may be placed in a helium-filled chamber with the first element of the camera serving as an optical window. A range of resolving powers from 23 000 to 100 000 will be possible with fibres having diameters of 300 to 400 μm and various combinations of fibre-exit micro-slits. It is possible to image the spectrum of a second object, the sky, or a calibration lamp at most resolving powers. Complete spectral coverage from 380 nm to 670 nm, and nearly complete coverage to 880 nm is possible with a mosaic of two 30.7 x 61.4-mm detectors. Some details of the expected performance of CELESTIA are presented. It is expected that the spectrograph will have a maximum efficiency of approximately 20%, not accounting for the atmosphere or telescope. This compares favourably with other existing spectrographs designed for large telescopes.