A new concept for echelle spectrographs: the SOAR Telescope Echelle Spectrograph

Abstract

We present the design of the SOAR Telescope Echelle Spectrograph (STELES). The instrument is part of the Brazilian participation on the 4.1m SOAR telescope second-generation instrumentation. A multi-institutional team is designing the echelle spectrograph with UV capability. In view of its high image quality and moderately large collecting area, SOAR will be able to yield high quality spectroscopic data for a large variety of objects of astrophysical interests. Another point that should be explored in SOAR is the near UV capability, not available in most of the current available high-resolution spectrographs. The proposed spectrograph is a R4 cross-dispersed echelle fed by the SOAR Nasmyth focus, operating in a quasi-Littrow white pupil configuration, and a resolving power of R ~ 50,000, covering the 300-890nm spectral range in one shot. The concept developed for this spectrograph is based on VPH grating crossdispersers and all spherical optics (including the collimator mirrors). The transfer collimator is mounted in a position so that the 100mm F/8.5 beam is resized to 50mm, allowing very compact cameras design. These modifications on the standard quasi-Littrow, white pupil configuration design yield a very efficient, compact and cheaper spectrograph.