Binospec: A Wide-field Imaging Spectrograph for the MMT.

Binospec is a high-throughput, 370 to 1000 nm, imaging spectrograph that addresses two adjacent 8' by 15' fields of view. Binospec was commissioned in late 2017 at the f/5 focus of the 6.5 m MMT and is now available to all MMT observers. Aperture masks cut from stainless steel with a laser cutter are used to define the entrance apertures that range from 15' long slits to hundreds of 2 " slitlets. System throughputs, including the MMT's mirrors and the f/5 wide-field corrector peak at similar to 30%. Three reflection gratings, duplicated for the two beams, provide resolutions (lambda/Delta lambda) between 1300 and >5000 with a 1 " wide slit. Two through-the-mask guiders are used for target acquisition, mask alignment, guiding, and precision offsets. A full-time Shack-Hartmann wavefront sensor allows continuous adjustment of primary minor support forces, telescope collimation and focus. Active flexure control maintains spectrograph alignment and focus under varying gravity and thermal conditions.