The Role of Dust Clouds in the Atmospheres of Brown Dwarfs

TL;DR

This paper discusses how dust clouds influence the spectral classes, colors, and spectra of brown dwarfs, highlighting the importance of condensation chemistry and grain properties in their atmospheres.

Contribution

It summarizes the role of dust clouds and refractory grains in defining the spectral classes and atmospheric properties of brown dwarfs, emphasizing recent developments.

Findings

Dust clouds define L and T spectral classes.

Silicate and iron grain condensation affects spectral transitions.

Dust properties influence brown dwarf colors and spectra.

Abstract

The new spectroscopic classes, L and T, are defined by the role of dust clouds in their atmospheres, the former by their presence and the latter by their removal and near absence. Moreover, the M to L and L to T transitions are intimately tied to the condensation and character of silicate and iron grains, and the associated clouds play pivotal roles in the colors and spectra of such brown dwarfs. Spanning the effective temperature range from $\sim$2200 K to $\sim$600 K, these objects are being found in abundance and are a new arena in which condensation chemistry and the optical properties of grains is assuming astronomical importance. In this short paper, I summarize the role played by such refractories in determining the properties of these "stars" and the complexities of their theoretical treatment.