The Substellar Transition Zone: A Stretched Temperature Canyon in Brown Dwarf Population due to Unsteady Hydrogen Fusion

TL;DR

This paper discusses the existence of a substellar transition zone caused by unsteady hydrogen fusion in brown dwarfs, affecting their temperature distribution and observational properties, especially in old halo populations.

Contribution

It introduces an L subdwarf classification scheme and characterizes the substellar transition zone caused by unsteady hydrogen fusion in brown dwarfs.

Findings

Transitional brown dwarfs have unsteady hydrogen fusion.

The temperature range of the transition zone is 1000 K to 3000 K.

The transition zone is prominent in old halo populations.

Abstract

I summarize results on transitional and degenerate brown dwarfs presented in a series titled Primeval very low-mass stars and brown dwarfs. I introduce an L subdwarf classification scheme, which classified L subdwarfs into three metal subclasses. I would also like to draw your attention to transitional brown dwarfs which have long-lasting unsteady hydrogen fusion in their cores to replenish the dissipation of their initial thermal energy. The mass range of transitional brown dwarfs with solar metallicity is between 0.065 and 0.079 solar mass according to the latest evolutionary models. The temperature distribution of transitional brown dwarfs are stretched to a wide range and formed a substellar transition zone. The substellar transition zone is most significant in the old halo population and ranges from 1000 K to 2200-3000 K depending on metallicity. The transition zone has impacts on our observational properties of field brown dwarf population. Because field L dwarfs are composed of very low-mass stars, transitional brown dwarfs, and relative younger electron-degenerate brown dwarfs.