SALT High Resolution Spectrograph (SALT-HRS)

The SALT-HRS is the last of 3 "first generation" SALT Instruments to be developed and initially suffered delays in due to both technical issues and lack of full funding. The critical design phase was completed by the University of Canterbury in 2005 and a call for tenders made in 2006 with CfAI being selected as the Prime Contractor later that year. Full funding for SALT-HRS was achieved in 2007, which was followed by the contract signing with CfAI.

The SALT-HRS design is for dual-beam fibre-fed white-pupil R4 echelle spectrograph, employing VPH gratings as cross dispersers. The cameras are all-refractive. The concept is for SALT-HRS to be an efficient single object spectrograph using pairs of large 300um to 500um (1.3-2.2") diameter optical fibers, one for source (star) and one for background (sky). Some of these will feed image slicers, allowing for up to 3 slices in the spatial direction, before injection into the spectrograph, which will deliver a range of resolving power of between R=17,00 (un-sliced 500um fibres) and 70,00. The wavelength coverage of the two beams, split by a dichroic, will be in the region 370-560nm (blue) and 560-870nm (red). A single 2K x 4K CCD will be sufficient to capture all the blue orders, while a 4K x 4K detector will be required for the red. Complete free spectral ranges are covered.

The spectrograph will be enclosed in a vacuum tank to improve stability of the instrument, and to ensure the optics remain in a pristine condition. It will be locaed in the SALT Spectrometer Room, underneath the telescope, in a temperature controlled enclosure. In addition, to allow for precise measurement of radial velocities (e.g. for exoplanet programmes), various additional features may be incorporated. To ensure accurate background subtraction, both beam switching and "nod & shuffle" techniques will be supported by HRS and Fibre Instrument Feed, mounted on the Prime Focus Payload.