Rotational Modulation of Spectroscopic Zeeman Signatures in Low-mass Stars

Ryan C. Terrien, Allison Keen, Katy Oda, Winter Partsthey/them, Guðmundur Stefánsson, Suvrath Mahadevan, Paul Robertson, Joe P. Ninan, Corey Beard, Chad F. Bender, William D. Cochran, Katia Cunha, Scott A. Diddams, Connor Fredrick, Samuel Halverson, Fred Hearty, Adam Ickler, Shubham Kanodia, Jessica E. Libby-Roberts, Jack LubinAndrew J. Metcalf, Freja Olsen, Lawrence W. Ramsey, Arpita Roy, Christian Schwab, Verne V. Smith, Ben Turner

Research output: Contribution to journalArticlepeer-review

9 Scopus citations


Accurate tracers of the stellar magnetic field and rotation are cornerstones for the study of M dwarfs and for reliable detection and characterization of their exoplanetary companions. Such measurements are particularly challenging for old, slowly rotating, fully convective M dwarfs. To explore the use of new activity and rotation tracers, we examined multiyear near-infrared (NIR) spectroscopic monitoring of two such stars-GJ 699 (Barnard's Star) and Teegarden's Star-carried out with the Habitable-zone Planet Finder spectrograph. We detected periodic variations in absorption line widths across the stellar spectrum, with higher amplitudes toward longer wavelengths. We also detected similar variations in the strength and width of the 12435.67 Å neutral potassium (K i) line, a known tracer of the photospheric magnetic field. Attributing these variations to rotational modulation, we confirm the known 145 ± 15 day rotation period of GJ 699, and measure the rotation period of Teegarden's Star to be 99.6 ± 1.4 days. Based on simulations of the K i line and the wavelength dependence of the line-width signal, we argue that the observed signals are consistent with varying photospheric magnetic fields and the associated Zeeman effect. These results highlight the value of detailed line profile measurements in the NIR for diagnosing stellar magnetic field variability. Such measurements may be pivotal for disentangling activity and exoplanet-related signals in spectroscopic monitoring of old, low-mass stars.

Original languageEnglish (US)
Article numberL11
JournalAstrophysical Journal Letters
Issue number1
StatePublished - Mar 1 2022

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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