Atmospheres of Brown Dwarfs

TL;DR

This paper reviews the atmospheres of Brown Dwarfs, highlighting their spectral characteristics, temperature-dependent cloud formation, and recent observations of plasma processes like radio emissions.

Contribution

It synthesizes current understanding of Brown Dwarf atmospheres, emphasizing the transition from star-like to planet-like spectra and recent plasma activity findings.

Findings

Brown Dwarfs exhibit a temperature-dependent spectral sequence.

Cloud formation occurs below 2800K in Brown Dwarf atmospheres.

Radio emissions indicate plasma processes in very cool atmospheres.

Abstract

Brown Dwarfs are the coolest class of stellar objects known to date. Our present perception is that Brown Dwarfs follow the principles of star formation, and that Brown Dwarfs share many characteristics with planets. Being the darkest and lowest mass stars known makes Brown Dwarfs also the coolest stars known. This has profound implication for their spectral fingerprints. Brown Dwarfs cover a range of effective temperatures which cause brown dwarfs atmospheres to be a sequence that gradually changes from a M-dwarf-like spectrum into a planet-like spectrum. This further implies that below an effective temperature of < 2800K, clouds form already in atmospheres of objects marking the boundary between M-Dwarfs and brown dwarfs. Recent developments have sparked the interest in plasma processes in such very cool atmospheres: sporadic and quiescent radio emission has been observed in combination with decaying Xray-activity indicators across the fully convective boundary.