CIRPASS : the Cambridge Infrared Panoramic Survey Spectrograph

The Cambridge Infrared Panoramic Survey Spectrograph, CIRPASS, is an infrared spectrograph that operates in the 0.9 to 1.8 mm wavelength region. CIRPASS was developed entirely at the Institute of Astronomy, Cambridge, and the design, construction and performance of CIRPASS are presented in this thesis. CIRPASS provides integral field spectroscopy (IFS). Spectra are simultaneously obtained from 499 contiguous spatial elements in a two-dimensional area of sky using an integral field unit (IFU). The construction of the IFU, which used a lenslet array and fibre optic bundle, is presented, as well as a review of IFS techniques. The sensitivity of CIRPASS has been maximised by ensuring the background signal detected by the instrument is reduced to an absolute minimum. CIRPASS has the capability to remove, both in hardware and software, the dominant infrared sky background from OH emission in the upper atmosphere. The advantages that this offers, and the benefits of both suppression techniques are presented. The thermal background of CIRPASS was reduced by cooling the entire spectrograph to -40°C. The instrument was cooled using a conventional industrial refrigeration system and resulted in significant improvements to the instrument's performance. The characteristics of the HAWAII infrared detector array used were measured, to determine their impact on the instrument's sensitivity, and found to be within specification. Software was written to reduce CIRPASS data that is applicable to any IFS instrument producing data in the Euro 3D format. A data reduction pipeline, that can be used for rapid data reduction at the telescope and for more detailed analysis afterwards, was implemented. The pipeline implementation and the techniques adopted for reducing closely packed spectral data on an infrared detector are discussed. The performance of CIRPASS was quantified by observing the Cambridge night sky with CIRPASS attached to a small telescope. The results provide an accurate measure of the instrument's performance on a larger telescope and are detailed. The expected limiting magnitudes for 3 hour observations of a point source, on an 8 m telescope, resulting in a signal-to-noise ratio of 5 are J=21.3 and H=19.3. The equivalent limiting line fluxes are J=4.4x10^-18 ergs/s/cm² and H=9.0x10^-8 ergs/s/cm².