Variability in SSTc2d J163134.1-240100, a brown dwarf with quasi-spherical mass loss

TL;DR

This study investigates variability in the young brown dwarf SST1624, finding no short-term periodic variability but detecting longer-term brightness changes likely caused by rotational modulation, which informs theories about its mass loss mechanisms.

Contribution

The paper provides new observational constraints on variability timescales in SST1624, challenging the role of centrifugal winds and supporting thermal pulses as the mass loss mechanism.

Findings

No variability detected on 1-6 hour timescales for amplitudes >1%.

Detected a 3% decrease in K-band magnitude over consecutive nights.

Observed day-scale variations consistent with rotational modulation due to spots.

Abstract

We report on a search for variability in the young brown dwarf SST1624 (~M7 spectral type, M~0.05Msol), previously found to feature an expanding gaseous shell and to undergo quasi-spherical mass loss. We find no variability on timescales of 1-6hours. Specifically, on these timescales, we rule out the presence of a period with amplitude >1%. A photometric period in that range would have been evidence for either pulsation powered by Deuterium burning or rotation near breakup. However, we see a 3% decrease in the K-band magnitude between two consecutive observing nights (a 10sigma result). There is also clear evidence for variations in the WISE lightcurves at 3.6 and 4.5 microns on timescales of days, with a tentative period of about 6d (with a plausible range between 3 and 7d). The best explanation for the variations over days is rotational modulation due to spots. These results disfavour centrifugal winds driven by fast rotation as mechanism for the mass loss, which, in turn, makes the alternative scenario -- a thermal pulse due to Deuterium burning -- more plausible.