Ultracool Subdwarfs: The Halo Population Down to the Substellar Limit

TL;DR

This paper reviews recent discoveries and research on ultracool subdwarfs, low-luminosity low-metallicity stars, highlighting their significance for understanding stellar atmospheres, evolution, and the halo population.

Contribution

It synthesizes recent observational and theoretical advances in ultracool subdwarfs, emphasizing their role in understanding low-metallicity stellar physics and halo population characteristics.

Findings

Insights into metallicity effects on atmospheres

Understanding of halo luminosity and mass functions

Advances in spectral classification and brightness scales

Abstract

Ultracool subdwarfs are low luminosity, late-type M and L dwarfs that exhibit spectroscopic indications of subsolar metallicity and halo kinematics. Their recent discovery and ongoing investigation have led to new insights into the role of metallicity in the opacity structure, chemistry (e.g. dust formation) and evolution of low-temperature atmospheres; the long-term evolution of magnetic activity and angular momentum amongst the lowest-mass stars; the form of the halo luminosity and mass functions down to the hydrogen-burning mass limit; and even fundamental issues such as spectral classification and absolute brightness scales. This Splinter Session was devoted to bringing advances in observational and theoretical ultracool subdwarf research to the attention of the low-mass stellar and brown dwarf communities, as well as to share results among ultracool subdwarf enthusiasts.