Binospec: A Wide-field Imaging Spectrograph for the MMT

TL;DR

Binospec is a versatile wide-field imaging spectrograph for the MMT, offering high throughput, adjustable resolution, and active alignment features, enabling efficient spectroscopic observations across two adjacent fields.

Contribution

This paper introduces Binospec, a new wide-field imaging spectrograph with high throughput, flexible slit configurations, and active flexure control, optimized for the MMT telescope.

Findings

System throughput peaks at ~30%.

Resolutions range from 1300 to over 5000.

Active flexure control maintains alignment under varying conditions.

Abstract

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 6.5m 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 ~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 wave front sensor allows continuous adjustment of primary mirror support forces, telescope collimation and focus. Active flexure control maintains spectrograph alignment and focus under varying gravity and thermal conditions.