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Title: Rotational Modulation of Spectroscopic Zeeman Signatures in Low-mass Stars
Abstract

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 (Ki) 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 Kiline 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 more » magnetic field variability. Such measurements may be pivotal for disentangling activity and exoplanet-related signals in spectroscopic monitoring of old, low-mass stars.

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Authors:
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Award ID(s):
2009554 2108493 2009507 2108801 2108569
Publication Date:
NSF-PAR ID:
10363518
Journal Name:
The Astrophysical Journal Letters
Volume:
927
Issue:
1
Page Range or eLocation-ID:
Article No. L11
ISSN:
2041-8205
Publisher:
DOI PREFIX: 10.3847
Sponsoring Org:
National Science Foundation
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