Exploring the Role of Sub-micron Sized Dust Grains in the Atmospheres of Red L0 - L6 Dwarfs

TL;DR

This study investigates how sub-micron dust grains in the upper atmospheres of L dwarfs influence their near-infrared colors, proposing a dust haze model that explains observed reddening effects.

Contribution

The paper introduces a novel model incorporating sub-micron dust grains to explain the reddening in L dwarf atmospheres, extending current models that only consider larger dust particles.

Findings

Sub-micron silicate grains can reproduce observed reddening.

Dust haze properties constrained using MCMC methods.

Results suggest combining large and small dust grains in models.

Abstract

We examine the hypothesis that the red near-infrared colors of some L dwarfs could be explained by a "dust haze" of small particles in their upper atmospheres. This dust haze would exist in conjunction with the clouds found in dwarfs with more typical colors. We developed a model which uses Mie theory and the Hansen particle size distributions to reproduce the extinction due to the proposed dust haze. We apply our method to 23 young L dwarfs and 23 red field L dwarfs. We constrain the properties of the dust haze including particle size distribution and column density using Markov-Chain Monte Carlo methods. We find that sub-micron range silicate grains reproduce the observed reddening. Current brown dwarf atmosphere models include large grain (1--100~$\mu m$) dust clouds but not submicron dust grains. Our results provide a strong proof of concept and motivate a combination of large and small dust grains in brown dwarf atmosphere models.