An Integral Field Unit for the Binospec Spectrograph

TL;DR

This paper describes the design, implementation, and commissioning of a new optical fiber-based integral field unit for the Binospec spectrograph at the MMT telescope, enabling spatially resolved spectroscopy within a compact footprint.

Contribution

It introduces a novel IFU that fits into a standard slit mask frame and can be deployed alongside other observing modes, enhancing Binospec's capabilities.

Findings

Successfully commissioned in 2023.

Supports multiple spectral resolutions.

Provides spatially resolved spectroscopy over a 12''x16'' region.

Abstract

Binospec is a wide-field optical (360 to 1000 nm) spectrograph commissioned at the MMT 6.5m telescope in 2017. In direct imaging mode Binospec addresses twin 8$^\prime$ (wide) by 15$^\prime$ (slit length) fields of view. We describe an optical fiber based integral field unit (IFU) that remaps a 12$^{\prime\prime}$ x 16$^{\prime\prime}$ contiguous region onto two pseudo slits, one in each Binospec channel. The IFU, commissioned in 2023, fits into the space of a standard slit mask frame and can be deployed as desired in a mixed program of slit masks, long slits, and IFU observations. The IFU fibers are illuminated by a hexagonal lenslet array with a 0.6$^{\prime\prime}$ pitch. A separate bundle of sky fibers consists of close-packed bare fibers arranged within an 11.8$^{\prime\prime}$ circular aperture. The 640 IFU fibers and 80 sky fibers have a core diameter of 150$\mu$m, corresponding to 0.90$^{\prime\prime}$. Three gratings are available, 270lpm with R$\sim$2000, 600lpm with R$\sim$5300, and 1000 lpm with R$\sim$6000.