The Commissioning Instrument for the Dark Energy Spectroscopic Instrument

TL;DR

The paper details the design of a commissioning instrument for DESI, which tests optical quality and coordinate mapping to ensure successful spectroscopic observations with the Mayall Telescope.

Contribution

It introduces a new commissioning instrument with multiple cameras and fiducials to characterize optical performance and coordinate mapping for DESI's spectroscopic survey.

Findings

Instrument successfully characterizes optical quality over the field of view.

Fiducials enable precise mapping between fiber positions and celestial coordinates.

Design reduces risks in the DESI commissioning process.

Abstract

We describe the design of the Commissioning Instrument for the Dark Energy Spectroscopic Instrument (DESI). DESI will obtain spectra over a 3 degree field of view using the 4-meter Mayall Telescope at Kitt Peak, AZ. In order to achieve the required image quality over this field of view, a new optical corrector is being installed at the Mayall Telescope. The Commissioning Instrument is designed to characterize the image quality of the new optical system. The Commissioning Instrument has five commercial cameras; one at the center of the focal surface and four near the periphery of the field and at the cardinal directions. There are also 22 illuminated fiducials, distributed throughout the focal surface, that will be used to test the system that will map between the DESI fiber positioners and celestial coordinates. We describe how the commissioning instrument will perform commissioning tasks for the DESI project and thereby eliminate risks.