The spectrograph is located on a 2m x 6m optical table in the telescope pier, inside a pressure- and temperature-stabilized chamber. It receives light from the polarimeters and permanent focus stations via 44m long fibres, coupled with image slicers. The polarimetric mode provides a resolution of 120.000, while resolutions of 40.000, 120.000 and 270.000 can be obtained with the permanent focus stations through a choice of different fibres. A white-pupil two-arm design with a 200mm main beam diameter, utilizing the largest available monolithic echelle grating and VPH grisms for cross dispersion, is employed. The collimators are nominally off-axis Maksutov systems, allowing for a beam diameter reduction to 125mm in the blue and red transfer collimator arms. The two spectrograph cameras are equipped with a single monolithic 10k x 10k CCD from STA (STA 1600LN). For each spectral order, four spectra are recorded, i.e. two polarization states or object/sky for each telescope. The entire spectral range from 383 to 912 nm can be covered in three exposures.
Overall spectrograph characteristics
|Fibre Diam. (μm)||Sky Diam.||# of slices (n)||Slicer Width (μm)||Slicer Width||R = λ/Δλ||R Sampl. (pix)|