Spectral Variability from the Patchy Atmospheres of T and Y Dwarfs

TL;DR

This paper models spectral variability in mid-late T and Y dwarfs caused by patchy clouds and temperature perturbations, highlighting the importance of multi-wavelength observations for understanding atmospheric dynamics.

Contribution

It introduces new models for variability in T and Y dwarfs including patchy salt, sulfide, and water clouds, and explores the effects of temperature perturbations at different atmospheric levels.

Findings

Patchy cloud opacity causes significant near-infrared variability in objects over 375 K.

Water clouds increase mid-infrared variability in cooler Y dwarfs.

Temperature perturbations produce variability strongest at absorption features.

Abstract

Brown dwarfs of a variety of spectral types have been observed to be photometrically variable. Previous studies have focused on objects at the L/T transition, where the iron and silicate clouds in L dwarfs break up or dissipate. However, objects outside of this transitional effective temperature regime also exhibit variability. Here, we present models for mid-late T dwarfs and Y dwarfs. We present models that include patchy salt and sulfide clouds as well as water clouds for the Y dwarfs. We find that for objects over 375 K, patchy cloud opacity would generate the largest amplitude variability within near-infrared spectral windows. For objects under 375 K, water clouds also become important and generate larger amplitude variability in the mid-infrared. We also present models in which we perturb the temperature structure at different pressure levels of the atmosphere to simulate hot spots. These models show the most variability in the absorption features between spectral windows. The variability is strongest at wavelengths that probe pressure levels at which the heating is the strongest. The most illustrative types of observations for understanding the physical processes underlying brown dwarf variability are simultaneous, multi-wavelength observations that probe both inside and outside of molecular absorption features.