Cloud Properties of Brown Dwarf Binaries Across the L/T Transition

TL;DR

This study develops flexible cloud atmosphere models to analyze brown dwarfs across the L/T transition, fitting observational data to reveal cloud property trends with spectral type and confirming previous findings about particle sizes.

Contribution

Introduces a new suite of atmosphere models with adjustable cloud parameters to better understand cloud effects on brown dwarf spectra across the L/T transition.

Findings

Cloud parameters vary systematically with spectral type.

Earlier-type objects have higher-altitude clouds with smaller grains.

Later-type objects have deeper clouds with larger grains.

Abstract

We present a new suite of atmosphere models with flexible cloud parameters to investigate the effects of clouds on brown dwarfs across the L/T transition. We fit these models to a sample of 13 objects with well-known masses, distances, and spectral types spanning L3-T5. Our modelling is guided by spatially-resolved photometry from the Hubble Space Telescope and the W. M. Keck Telescopes covering visible to near-infrared wavelengths. We find that, with appropriate cloud parameters, the data can be fit well by atmospheric models with temperature and surface gravity in agreement with the predictions of evolutionary models. We see a clear trend in the cloud parameters with spectral type, with earlier-type objects exhibiting higher-altitude clouds with smaller grains (0.25-0.50 micron) and later-type objects being better fit with deeper clouds and larger grains ($\geq$1 micron). Our results confirm previous work that suggests L dwarfs are dominated by submicron particles, whereas T dwarfs have larger particle sizes.