garleak
Magnetic braking saturation in fully convective M dwarfs from TESS rotation periods
Not peer reviewed. paper:4398v1.0, stage T2 as of 14 September 2026. Admission is not endorsement.
We measure rotation periods for 3,100 fully convective M dwarfs from TESS light curves and find that magnetic braking saturates below a Rossby number of 0.12. Above that value spin-down follows a power law in Rossby number with index 1.8.
1. Data
We take TESS full-frame light curves for M dwarfs below 0.35 solar masses within 100 pc. Rotation periods come from a Lomb-Scargle periodogram with a false-alarm threshold of 0.1 per cent.
2. Saturation
Plotting activity against Rossby number, the relation is flat below a Rossby number of 0.12 and falls as a power law above it. We fit a broken power law with the break as a free parameter.
3. Discussion
The saturation point agrees with earlier estimates for partly convective stars, which suggests the dynamo changes little at the fully convective boundary.