# The Rotation-Disk Connection in Young Brown Dwarfs: Strong Evidence for Early Rotational Braking

## TL;DR

This study uses Kepler/K2 data to measure rotation periods of young brown dwarfs and low-mass stars, providing strong evidence that early disk interactions significantly slow down their rotation during the first few million years.

## Contribution

It presents the first comprehensive measurement of rotation periods for a large sample of young brown dwarfs, demonstrating early rotational braking caused by disk interactions.

## Key findings

- Brown dwarfs show longer rotation periods if they have disks.
- Evidence of disk-locking observed in lightcurves of two brown dwarfs.
- Rotational braking must be included in models of early brown dwarf evolution.

## Abstract

We use Kepler/K2 lightcurves to measure rotation periods of brown dwarfs and very low mass stars in the Upper Scorpius star-forming region. Our sample comprises a total of 104 periods. Depending on the assumed age of Upper Scorpius, about a third of them are for brown dwarfs. The median period is 1.28 d for the full sample and 0.84 d for the probable brown dwarfs. With this period sample, we find compelling evidence for early rotational braking in brown dwarfs, caused by the interaction between the central object and the disk. The median period for objects with disks is at least 50% longer than for those without. Two brown dwarfs show direct signs of 'disk-locking' in their lightcurves, in the form of dips that recur on a timescale similar to the rotation period. Comparing the period samples for brown dwarfs at different ages, there is a clear need to include rotational braking into period evolution tracks between 1 and 10 Myr. A locked period over several Myr followed by spin-up due to contraction fits the observational data. We conclude that young brown dwarfs are affected by the same rotational regulation as stars, though they start off with significantly faster rotation, presumably set by initial conditions.