SparsePak: A Formatted Fiber Field Unit for the WIYN Telescope Bench Spectrograph. I. Design, Construction, and Calibration

We describe the design and construction of a formatted fiber field-unit, SparsePak, and characterize its optical and astrometric performance. This array is optimized for spectroscopy of low-surface brightness, extended sources in the visible and near-infrared. SparsePak contains 82, 4.7" fibers subtending an area of 72"x71" in the telescope focal plane, and feeds the WIYN Bench spectrograph. Together, these instruments are capable of achieving spectral resolutions of lambda/dlambda ~ 20000 and an area--solid-angle product of ~140 arcsec^2 m^2 per fiber. Laboratory measurements of SparsePak lead to several important conclusions on the design of fiber termination and cable curvature to minimize focal ratio…