Metal-Depleted Brown Dwarfs

TL;DR

This paper reviews the current understanding of metal-poor ultracool dwarfs, focusing on their spectral characteristics, classification, physical parameters, and future research directions to better comprehend the Galaxy's oldest objects.

Contribution

It provides a comprehensive overview of metal-poor ultracool dwarfs, including their spectral features, classification challenges, and physical parameter estimation methods, highlighting areas for future study.

Findings

Color trends from optical to mid-infrared identified

Spectral features used for tentative classification

Discussion on physical parameters and future research directions

Abstract

This chapter reviews our current knowledge of metal-poor ultracool dwarfs with spectral types later than M7. The current census of M, L, and T subdwarfs is explored. The main colour trends of subdwarfs from the optical to the mid-infrared are described and their spectral features presented, which led to a preliminary and tentative spectral classification subject to important changes in the future when more of these metal-poor objects are discovered. Their multiplicity and the determination of their physical parameters (effective temperature, gravity, metallicity, and mass) are discussed. Finally, some suggestions and future guidelines are proposed to foster our knowledge on the oldest and coolest members of our Galaxy.