Rotation Periods of Young Brown Dwarfs: K2 Survey in Upper Scorpius

TL;DR

This study measures rotation periods of 16 young brown dwarfs in Upper Scorpius using Kepler K2 data, revealing they are generally fast rotators with limited evidence of disk braking, contrasting with low-mass stars.

Contribution

First detailed rotation period measurements of young brown dwarfs in Upper Scorpius, showing limited rotational braking and providing constraints on substellar angular momentum evolution.

Findings

Brown dwarfs have rotation periods from hours to two days.

Limited evidence of rotational braking in brown dwarfs aged 1-10 Myr.

Disk presence correlates with slower rotation in some brown dwarfs.

Abstract

We report rotational periods for 16 young brown dwarfs in the nearby Upper Scorpius association, based on 72 days of high-cadence, high-precision photometry from the Kepler space telescope's K2 mission. The periods range from a few hours to two days (plus one outlier at 5 days), with a median just above one day, confirming that brown dwarfs, except at the very youngest ages, are fast rotators. Interestingly, four of the slowest rotators in our sample exhibit mid-infrared excess emission from disks; at least two also show signs of disk eclipses and accretion in the lightcurves. Comparing these new periods with those for two other young clusters and simple angular momentum evolution tracks, we find little or no rotational braking in brown dwarfs between 1-10 Myr, in contrast to low-mass stars. Our findings show that disk braking, while still at work, is inefficient in the substellar regime, thus provide an important constraint on the mass dependence of the braking mechanism.