Khayyam, a tunable, cyclical spatial heterodyne spectrometer on Mt. Hamilton

Abstract

We describe the design considerations, installation, and technical challenges of coupling a cyclical spatial heterodyne spectrometer (SHS) with the Cassegrain telescope at the Lick Observatory on Mt. Hamilton, California. The SHS instrument (named Khayyam after the mathematician) is mounted to a fixed focal plane shared by the 0.6-m Cassegrain Coude Auxiliary Telescope (CAT) and has the field-of-view of ∼4 arc min, on the sky, spectral resolving power (R) of 48,000 and a tunable wavelength bandpass range over ΔλB ∼ 150 Å. This instrument–telescope pairing is optimal for temporal observations of extended astronomical targets, e.g., cometary coma, when significant observing time is available since it provides high-resolution spectra from small input apertures. Khayyam’s approach contrasts with traditional high spectral resolution spectrometers that need to be coupled to large aperture telescopes to compensate for their low throughput. Based on our reference lamp results, we were able to formulate the undesirable impact of the spider pattern on the SHS data that prohibited us from acquiring spectra from our sky targets. However, more analysis is needed to investigate if we can create a framework to systematically eliminate the diffracted spider pattern shadow from the fringe pattern without compromising the integrity and quality of the data.