The L dwarf/T dwarf transition: multiplicity, magnetic activity and mineral meteorology across the hydrogen burning limit

TL;DR

The paper explores the complex L/T dwarf transition, highlighting phenomena like brightening, increased multiplicity, and variability, explained by rapid cloud rainout influenced by physical parameters, and discusses its significance for understanding brown dwarf evolution.

Contribution

It provides a comprehensive review of the L/T transition phenomena and proposes cloud rainout as a key mechanism, advancing understanding of brown dwarf atmospheric and evolutionary processes.

Findings

Brightening observed in late L to early T dwarfs

Spike in multiplicity fraction during transition

Increased photometric variability linked to patchy clouds

Abstract

The transition between the L dwarf and T dwarf spectral classes is one of the most remarkable along the stellar/brown dwarf Main Sequence, separating sources with photospheres containing mineral condensate clouds from those containing methane and ammonia gases. Unusual characteristics of this transition include a 1 micron brightening between late L and early T dwarfs observed in both parallax samples and coeval binaries; a spike in the multiplicity fraction; evidence of increased photometric variability, possibly arising from patchy cloud structures; and a delayed transition for young, planetary-mass objects. All of these features can be explained if this transition is governed by the "rapid" (nonequlibrium) rainout of clouds from the photosphere, triggered by temperature, surface gravity, metallicity and (perhaps) rotational effects. While the underlying mechanism of this rainout remains under debate, the transition is now being exploited to discover and precisely characterize tight (< 1 AU) very low-mass binaries that can be used to test brown dwarf evolutionary and atmospheric theories, and resolved binaries that further constrain the properties of this remarkable transition.