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Understanding the Spindown History of M Dwarfs Using Wide Field Binaries

Presentation #102.305 in the session Poster Session.

Published onJun 20, 2022
Understanding the Spindown History of M Dwarfs Using Wide Field Binaries

M dwarfs remain active over longer timescales than their Sunlike counterparts, with potentially devastating implications for the atmospheres of their planets. However, the age at which fully-convective M dwarfs transition from active and rapidly rotating to quiescent and slowly rotating is poorly understood, as these stars remain rapidly rotating in the oldest clusters that are near enough for a large sample of low-mass M dwarfs to be studied (600-800 Myr). Rapidly-rotating M dwarfs are frequently identified in the field, although the ages of these stars are unknown. To place constraints on the spindown of these low-mass stars, we are studying the rotation periods of field M dwarfs in wide binary systems. Our analysis includes M-M pairs, which are coeval but of unknown age, as well as M dwarfs with white dwarf or Sunlike primaries, for which we can estimate ages using techniques like white dwarf cooling curves, gyrochronology, and lithium abundance. We find evidence for some variability in the spindown of fully-convective M dwarfs, with a small number of stars having substantially spun down at ages < 1 Gyr. However, this effect must be subtle enough to not obscure the strong correlation between rotation rate and stellar mass; in almost all of our studied M-M pairs where spindown is ongoing (2 < Prot < 40 days), the more massive star rotates more slowly, a correlation that indicates the variability in the age at spin down is small compared to the increase in spin down time with decreasing stellar mass. Nevertheless, this variability in M dwarf spindown history may help to explain how some highly-irradiated sub-Neptunes have seemingly retained massive H/He envelopes.

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