Stellar activity manifesting at a one-year alias explains Barnard b as a false positive

Jack Lubin, Paul Robertson, Gudmundur Stefansson, Joe Ninan, Suvrath Mahadevan, Michael Endl, Eric Ford, Jason T. Wright, Corey Beard, Chad Bender, William D. Cochran, Scott A. Diddams, Connor Fredrick, Samuel Halverson, Shubham Kanodia, Andrew J. Metcalf, Lawrence Ramsey, Arpita Roy, Christian Schwab, Ryan Terrien

    Research output: Contribution to journalArticlepeer-review

    25 Citations (Scopus)


    Barnard's star is among the most studied stars given its proximity to the Sun. It is often considered the radial velocity (RV) standard for fully convective stars due to its RV stability and equatorial decl. Recently, an M sin i=3.3M super-Earth planet candidate with a 233 day orbital period was announced by Ribas et al. New observations from the near-infrared Habitable-zone Planet Finder (HPF) Doppler spectrometer do not show this planetary signal. We ran a suite of experiments on both the original data and a combined original + HPF data set. These experiments include model comparisons, periodogram analyses, and sampling sensitivity, all of which show the signal at the proposed period of 233 days is transitory in nature. The power in the signal is largely contained within 211 RVs that were taken within a 1000 day span of observing. Our preferred model of the system is one that features stellar activity without a planet. We propose that the candidate planetary signal is an alias of the 145 day rotation period. This result highlights the challenge of analyzing long-term, quasi-periodic activity signals over multiyear and multi-instrument observing campaigns.

    Original languageEnglish
    Article number61
    Pages (from-to)1-16
    Number of pages16
    JournalAstronomical Journal
    Issue number2
    Publication statusPublished - Aug 2021


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