The NEID precision radial velocity spectrometer: project overview and status update (Conference Presentation)

Abstract

NEID is an ultra-stabilized, high-resolution, fiber-fed, spectrometer being built by a multi-institutional team for the 3.5 m WIYN telescope at Kitt Peak National Observatory, with a delivery date in 2019. The instrument is supported by the NN-EXPLORE program, a joint endeavor between NASA and the NSF to provide the exoplanet community with extreme ground-based Doppler radial velocity (RV) measurement capability. NEID's primary science objective is the discovery and characterization of terrestrial mass exoplanets, including follow-up of planets discovered by TESS and other spacecraft missions. Achieving these goals requires a multi-faceted approach that combines a state of the art Doppler instrument with a RV precision goal of 30 cm/s, a significantly improved understanding of the stellar radial velocity signal and intrinsic stellar variability, and large numbers of observations distributed optimally in time following guidelines refined over the past 25 years of RV exoplanet discovery. NEID uses a single-arm white pupil echelle optical design to produce R~100,000 spectra covering the complete wavelength range from 0.38 - 0.92 microns on a single 9k x 9k CCD. The optical bench and optics are stabilized with a state of the art temperature control system that achieves sub-mK stability, and are surrounded by a vacuum chamber that maintains 10^-7 Torr pressure or better. This extreme stability minimizes drift in the optics and optomechanical systems. Light is transfered from the telescope to the spectrometer using fiber-optic feeds that combine circular and octagonal fibers with a ball-lens double scrambler to provide high amounts of radial and azmuthal scrambling that minimize variations in the input illumination. These fibers interface with the WIYN telescope through a sophisticated new instrument port, which will provide atmospheric-dispersion correction and active tip-tilt to ensure precise and repeatable target positioning on the fiber. A three tiered calibration system utilizes a Laser Frequency Comb as the primary wavelength calibrator, while providing a stabilized etalon and ThAr and UNe Hollow-Cathode Lamps as high-reliability backup sources. An integrated exposure meter in the form of a low-resolution spectrometer measures precise chromatic exposure time centroids. A sophisticated data reduction pipeline that builds upon algorithms developed over decades of precision RV spectroscopy will automatically transform raw images and telemetry into RVs and other high-level data products, which will be served to users and the community through a NExScI portal. In this paper, we will provide an overview of the NEID project, including a progress update on the instrument integration and testing. We will also describe the WIYN operations plan, which is built around queue scheduled observations, and detail notional science programs that can be carried out with NEID, including the instrument team's GTO program. Finally, we will briefly discuss the impacts of stellar variability, which currently limit RV measurement precision well shy of the fundamental instrument limit, and which we and others are actively working to better understand and mitigate. Additional papers in this conference will describe the instrument subsystems in more detail.