2020/03/19 by Ryan R. Petersburg, J. M. Joel Ong, Lily L. Zhao +13 · 1 citation
Physics and Astronomy · #astro-ph.IM #astro-ph.EP #astro-ph.SR
paper · pdf · doi:10.3847/1538-3881/ab7e31
arxiv created 2020/03/19 · arxiv updated 2020/04/08
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 30\mathrm~cm~s-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 0.3\mathrm~m~s-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 0.895\mathrm~m~s-1.