The Extreme Stellar-signals Project. III. Combining Solar Data from HARPS, HARPS-N, EXPRES, and NEID

Lily L. Zhao, Xavier Dumusque, Eric B. Ford, Joe Llama, Annelies Mortier, Megan Bedell, Khaled Al Moulla, Chad F. Bender, Cullen H. Blake, John M. Brewer, Andrew Collier Cameron, Rosario Cosentino, Pedro Figueira, Debra A. Fischer, Adriano Ghedina, Manuel Gonzalez, Samuel Halverson, Shubham Kanodia, David W. Latham, Andrea S.J. LinGaspare Lo Curto, Marcello Lodi, Sarah E. Logsdon, Christophe Lovis, Suvrath Mahadevan, Andrew Monson, Joe P. Ninan, Francesco Pepe, Rachael M. Roettenbacher, Arpita Roy, Nuno C. Santos, Christian Schwab, Guđmundur Stefánsson, Andrew E. Szymkowiak, Ryan C. Terrien, Stephane Udry, Sam A. Weiss, François Wildi, Thibault Wildi, Jason T. Wright

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


We present an analysis of Sun-as-a-star observations from four different high-resolution, stabilized spectrographs—HARPS, HARPS-N, EXPRES, and NEID. With simultaneous observations of the Sun from four different instruments, we are able to gain insight into the radial velocity precision and accuracy delivered by each of these instruments and isolate instrumental systematics that differ from true astrophysical signals. With solar observations, we can completely characterize the expected Doppler shift contributed by orbiting Solar System bodies and remove them. This results in a data set with measured velocity variations that purely trace flows on the solar surface. Direct comparisons of the radial velocities measured by each instrument show remarkable agreement with residual intraday scatter of only 15-30 cm s−1. This shows that current ultra-stabilized instruments have broken through to a new level of measurement precision that reveals stellar variability with high fidelity and detail. We end by discussing how radial velocities from different instruments can be combined to provide powerful leverage for testing techniques to mitigate stellar signals.

Original languageEnglish (US)
Article number173
JournalAstronomical Journal
Issue number4
StatePublished - Oct 1 2023

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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