An Extreme-precision Radial-velocity Pipeline: First Radial Velocities from EXPRES

Ryan R. Petersburg, J. M. Joel Ong, Lily L. Zhao, Ryan T. Blackman, John M. Brewer, Lars A. Buchhave, Samuel H. C. Cabot, Allen B. Davis, Colby A. Jurgenson, Christopher Leet, Tyler M. McCracken, David Sawyer, Mikhail Sharov, René Tronsgaard, Andrew E. Szymkowiak, Debra A. Fischer*

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

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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 near Flagstaff, Arizona. The spectrograph was designed with a target radial-velocity (RV) precision of 30 cm s−1. In addition to instrumental innovations, the EXPRES pipeline, presented here, is the first 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 RV 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 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 m s−1.
Original languageEnglish
Article number187
JournalAstrophysical Journal
Issue number5
Number of pages14
Publication statusPublished - 2020


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