Performance of the Keck long wavelength spectrometer Original Research Article

The W.M. Keck Observatory’s Long Wavelength Spectrometer (LWS), is the mid-infrared facility instrument for imaging and low to moderate resolution spectroscopy for the wavelength range of 3–28 μm. At the heart of LWS is an 128 × 128 Si:As blocked impurity band (BIB) array. The detector is a moderate flux device with a 4-channel readout and well capacity of 1 × 107 e− making it properly suited for the thermal background environment for a ground based imaging spectrometer. The commissioned instrument, mounted on the Keck I 10-m telescope, delivers diffraction-limited images of 0.29″ FWHM at 11.7 μm. An overview of the performance characteristics of instrument and telescope are discussed including a detailed analysis of telescope emissivity. LWS scientific programs cover a broad range of topics that extend from the Solar System to extragalactic cosmology. This paper includes three examples that demonstrate the capabilities of Keck I and LWS: a high resolution mapping of the Titan atmosphere, a spectroscopic and imaging study of the compact nebula around the super massive binary RY Scuti, and high resolution imaging of a gravitational lensed quasi-stellar object QSO 2237+0305.