Spector: integration and performance of the multi-object spectrograph for the Anglo-Australian Telescope

The Hector instrument was installed at the Anglo-Australian Telescope in December 2021. All major subsystems, namely, the positioner, spectrograph and optical cable, performed as expected and the instrument received the first light. Spector is the new spectrograph with an average spectral resolution of R=4500 complementing the existing lower resolution AAOmega facility. Instrument design was optimized for hexabundles, the integral field units capturing telescope output. Fibers are arranged along a curved slit and a spherical focal surface at precise spacing to minimize cross talk. Details of the integration and testing of the spectrograph optics are presented here. Optical elements were manufactured externally, then aligned and assembled in-house. The spectrograph cameras work with an 180 mm pupil in a fast F/1.3 beam. Extreme sensitivity to errors requires lens positioning to 10 micron accuracy in decenter. The detector windows are aspheric and tilted and decentered with respect to the optical axis of the cameras. An alignment procedure was developed to measure and correct critical parameters of the system. Precision alignment is implemented in the lab, each optics mounts on the instrument structure kinematically allowing quick installation at a telescope site already aligned. Each assembled subsystem, 2 collimators and 2 cameras, was interferometrically checked for wavefront quality. Double path tests with null lenses and measured wavefront errors are discussed. The system spectral performance was fine tuned using a test fiber slit to achieve required resolution across the field of view. The absolute transmittance of the spectrograph bulk optics was measured in both blue and red channels over wavelength and compared to the predicted values.