The EXtreme PREcision Spectrograph (EXPRES) is an environmentally stabilized, fiber-fed, R=137,500, optical spectrograph. It was recently commissioned at the 4.3-m Lowell Discovery Telescope (LDT) near Flagstaff, Arizona. The spectrograph was designed with a target radial-velocity (RV) precision of 30cms−1. In addition to instrumental innovations, the EXPRES pipeline, presented here, is the first for an on-sky, optical, fiber-fed spectrograph to employ many novel techniques---including an "extended flat" fiber used for wavelength-dependent quantum efficiency characterization of the CCD, a flat-relative optimal extraction algorithm, chromatic barycentric corrections, chromatic calibration offsets, and an ultra-precise laser frequency comb for wavelength calibration. We describe the reduction, calibration, and radial-velocity analysis pipeline used for EXPRES and present an example of our current sub-meter-per-second RV measurement precision, which reaches a formal, single-measurement error of 0.3ms−1 for an observation with a per-pixel signal-to-noise ratio of 250. These velocities yield an orbital solution on the known exoplanet host 51 Peg that matches literature values with a residual RMS of 0.895ms−1.
@article{arxiv.2003.08851,
title = {An Extreme Precision Radial Velocity Pipeline: First Radial Velocities from EXPRES},
author = {Ryan R. Petersburg and J. M. Joel Ong and Lily L. Zhao and Ryan T. Blackman and John M. Brewer and Lars A. Buchhave and Samuel H. C. Cabot and Allen B. Davis and Colby A. Jurgenson and Christopher Leet and Tyler M. McCracken and David Sawyer and Mikhail Sharov and René Tronsgaard and Andrew E. Szymkowiak and Debra A. Fischer},
journal= {arXiv preprint arXiv:2003.08851},
year = {2020}
}