Rotation Periods of Candidate Single Late-M Dwarfs in TESS

TL;DR

This study measures rotation periods of 399 late-M dwarfs using TESS data, revealing a wide range of rotation timescales and supporting the idea that spot-induced variability is common in these low-mass stars.

Contribution

It provides a large, refined set of rotation periods for late-M dwarfs, expanding the known sample and confirming the trend of decreasing rotation period with later spectral types.

Findings

133 rotation periods identified, ranging from 2 hours to 6 days.

Variability detection increases with more TESS sectors, approaching 50%.

Lower envelope of rotation period decreases from 5 hours at early-M to 1 hour at L, T, Y dwarfs.

Abstract

Recent studies suggest that the angular momentum evolution of late-M and brown dwarfs differs from the well-known spin-down evolution of hotter stars. Characterizing the distribution of rotation periods of these objects in the solar neighborhood can help elucidate this evolutionary pathway just above, at, and below the hydrogen burning limit. In this paper, we examine 399 candidate single late-M dwarfs with $G - G_{RP} \geq 1.4$ mag ($\gtrsim$M6) using TESS light curves. To determine rotation periods, we employed Lomb-Scargle Periodograms to provide a first estimate of the period, then refined them with a Gaussian Process approach, requiring multi-sector confirmation when available. We found 133 rotation periods, ranging from 2 hours to 6 days, and amplitudes between 0.08% and 2.71%. We find that the observed variability fraction in late-M dwarfs rises with the number of available TESS sectors, approaching an apparent ceiling of ~50%. This likely reflects a detection limit determined by viewing geometry and supports the idea that spot-induced variability is common across the late-M and brown dwarf population. In our comparison with previously published late-M dwarf rotation periods reported, we found consistent results, confirming or updating 31 periods. Our findings expand the number of previously known late-M dwarf periods under 1 day by 76%. Combined with published rotation periods for a broader range of spectral types, we find a lower envelope on the rotation period decreasing from 5 hours at early-M dwarfs to 1 hour at L, T, and Y dwarfs.