Presentation #102.357 in the session Poster Session.
The focus on M dwarfs as planet hosts has led to a number of high-precision spectroscopic surveys monitoring M dwarfs to detect the Doppler radial-velocity signature of planets, including with the near-infrared Habitable Zone Planet Finder (HPF) instrument. In this work, we study the variability of the K I 12435.67Å line in spectra of two M dwarfs — GJ 699 (Barnard’s Star) and Teegarden’s Star — and we attribute these changes to Zeeman splitting. Using the Non-LTE Inversion COde using the Lorien Engine (NICOLE), we modeled the shape of the K I line under the influence of the Zeeman effect for various configurations of the magnetic field on the surfaces of Barnard’s star and Teegarden’s star. Comparing measurements of the K I line’s equivalent width and full width at half maximum in our NICOLE simulations to measurements of the same line in Habitable zone Planet Finder (HPF) spectra of the two stars over multiple years, we find that our models encompassed the range of variation seen in the data. The temporal behavior of these variations matches line width changes across the spectrum, as would be expected with rotationally modulated photospheric magnetic field changes. Our results demonstrate that detailed line profile measurements and modeling the Zeeman effect in near infrared lines are useful for analyzing stellar magnetic variability even for some of the slowest rotating stars. The techniques demonstrated here hold promise for future efforts to separate exoplanet radial velocity signals from noise introduced by magnetic activity of their host stars.