A Patchy Cloud Model for the L to T Dwarf Transition

TL;DR

This paper introduces a new model for partly cloudy brown dwarfs, showing that small cloud holes significantly impact their spectra and colors, providing insights into the L to T dwarf transition.

Contribution

The paper presents a self-consistent atmospheric model for partly cloudy brown dwarfs, highlighting the effects of cloud holes on observable properties and offering explanations for spectral features.

Findings

Small cloud holes dramatically change spectra and colors.

Partly cloudy models mimic thinner, globally homogeneous clouds.

Variability and polarization could indicate partial cloud cover.

Abstract

One of the mechanisms suggested for the L to T dwarf spectral type transition is the appearance of relatively cloud-free regions across the disk of brown dwarfs as they cool. The existence of partly cloudy regions has been supported by evidence for variability in dwarfs in the late L to early T spectral range, but no self-consistent atmosphere models of such partly cloudy objects have yet been constructed. Here we present a new approach for consistently modeling partly cloudy brown dwarfs and giant planets. We find that even a small fraction of cloud holes dramatically alter the atmospheric thermal profile, spectra, and photometric colors of a given object. With decreasing cloudiness objects briskly become bluer in J - K and brighten in J band, as is observed at the L/T transition. Model spectra of partly cloudy objects are similar to our models with globally homogenous, but thinner, clouds. Hence spectra alone may not be sufficient to distinguish partial cloudiness although variability and polarization measurements are potential observational signatures. Finally we note that partial cloud cover may be an alternative explanation for the blue L dwarfs.