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Evaluating Rotation Periods of M Dwarfs

Presentation #415.03 in the session “Stellar Rotation, Variability, and Flares 1”.

Published onJan 11, 2021
Evaluating Rotation Periods of M Dwarfs

M dwarfs are largely missing from standard gyrochronology relations, the relationship between the rotation rate of a star and its age. The decrease in angular momentum over time due to stellar winds interacting with the stellar magnetic field causes young rapidly rotating stars to slow down overtime, but the timescale for this spin down for M dwarfs is much longer than for solar mass stars. M dwarfs intrinsic brightness limits which objects can be observed, and there is also a shift from partially to fully convective interiors within the M dwarf regime which could impact the stellar dynamo or pathways for angular momentum exchange. Although these issues create a greater challenge to define these relations, their abundance and propensity for hosting rocky planets means calibrating the age-rotation rate relation would be a valuable tool for understanding M dwarfs.

We take M dwarf rotation rates from the literature for ten young and intermediate age clusters and associations as well as six older field samples and match them to Gaia DR 2 sources. We use Gaia DR 2 photometry and analyze how their rotation period varies with color, absolute magnitude, kinematics, and Halpha equivalent width measurements where available. We comment on the color and age dependence in clusters for where the transition from fast rotators to the slow rotator sequence occurs in early to mid Ms and its association with Halpha inactivity. Using kinematics we also find indications of this transition happening much later for late M dwarfs.

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