Khayyam: A second generation tunable spatial heterodyne spectrometer for broadband observation of diffuse emission line targets

We report on progress toward development of a second-generation tunable spatial heterodyne spectrometer (TSHS) at the fixed focus of the Coudé Auxiliary Telescope (CAT) in the Shane observatory at Lick Observatory (Khayyam). SHS instruments are a class of interferometric sensor capable of providing a combination of large étendue, high resolving power (R=λ/dλ∼10⁵) and wide field of view (FOV∼0.5 degree) at Optical and NUV wavelengths in a compact format. The TSHS implementation addresses the bandpass limitation of the basic SHS through controlled rotation of pilot mirrors in the interferometer. The use of a single grating as both a dispersing and beam-splitting element in the all-reflective SHS greatly relaxes the precision required in the alignment of the other optical elements relative to a more typical scanning Fourier Transform Spectrometer and allows the TSHS implementation to be accomplished with low-cost commercial rotation stages. The new design builds on a previous design originally tested in 2007, and will address several issues identified with the input beam, output imaging, and grating efficiency (Dawson and Harris, 2009). Here we will discuss the design considerations going into this new system and the initial results of the installation and testing of the TSHS and the future plans.