[Paper Review] The DESI Experiment Part II: Instrument Design

DESI Collaboration, Amir Aghamousa+291 more|arXiv (Cornell University)|Oct 31, 2016

Astronomy and Astrophysical Research30 references227 citations

TL;DR

This paper presents the DESI instrument design: a robotically-actuated, fiber-fed spectrograph system that can take up to 5,000 simultaneous spectra across 360–980 nm, feeding ten spectrographs to enable a large, five-year redshift survey on the Mayall telescope. It covers the Corrector, Focal Plane, Fiber System, Spectrographs, readout/control, data systems, and integration/testing.

ABSTRACT

DESI (Dark Energy Spectropic Instrument) is a Stage IV ground-based dark energy experiment that will study baryon acoustic oscillations and the growth of structure through redshift-space distortions with a wide-area galaxy and quasar redshift survey. The DESI instrument is a robotically-actuated, fiber-fed spectrograph capable of taking up to 5,000 simultaneous spectra over a wavelength range from 360 nm to 980 nm. The fibers feed ten three-arm spectrographs with resolution $R= λ/Δλ$ between 2000 and 5500, depending on wavelength. The DESI instrument will be used to conduct a five-year survey designed to cover 14,000 deg$^2$. This powerful instrument will be installed at prime focus on the 4-m Mayall telescope in Kitt Peak, Arizona, along with a new optical corrector, which will provide a three-degree diameter field of view. The DESI collaboration will also deliver a spectroscopic pipeline and data management system to reduce and archive all data for eventual public use.

Motivation & Objective

• Motivate the DESI Instrument design to enable a Stage IV dark energy survey of 14,000 deg^2.
• Describe the full instrument architecture, including optics, focal plane, fiber system, and spectrographs.
• Outline the readout, control systems, data management, and integration/testing plan for commissioning.

Proposed method

• Describe the Corrector development and its role in achieving a three-degree field of view.
• Detail the Focal Plane System, Fiber System, and ten three-arm spectrographs configuration.
• Explain the Instrument Readout and Control System and the Data Systems intended for data reduction and archiving.
• Summarize the Integration, Test, and Commissioning plan for deploying DESI on the Mayall telescope.

Experimental results

Research questions

• RQ1 How can an instrument be designed to deliver up to 5,000 simultaneous spectra over 360–980 nm?
• RQ2 What are the key subsystems (Corrector, Focal Plane, Fiber System, Spectrographs) and how do they integrate to meet survey requirements?
• RQ3 How will the data reduction pipeline and data management system support a large public spectroscopic survey?
• RQ4 What integration, testing, and commissioning strategies are required for a robust deployment on the Mayall telescope?

Key findings

• DESI is a robotically-actuated, fiber-fed spectrograph system capable of up to 5,000 simultaneous spectra.
• The instrument covers a wavelength range from 360 nm to 980 nm and feeds ten three-arm spectrographs with resolution varying with wavelength (R between 2000 and 5500).
• The DESI instrument will be installed at prime focus on the 4-m Mayall telescope in Arizona with a new optical corrector providing a three-degree field of view.
• A dedicated spectroscopic pipeline and data management system will be delivered to reduce and archive all data for eventual public use.
• The design is organized into sections: Corrector, Focal Plane System, Fiber System, Spectrographs, Instrument Readout and Control System, Data Systems, and Integration and Test, followed by Commissioning.