2MASS J06164006-6407194: The First Outer Halo L Subdwarf

TL;DR

This paper reports the discovery of the first outer halo L subdwarf, characterized by its unique spectral features and kinematic properties indicating membership in the galaxy's outer halo.

Contribution

The discovery of 2MASS J06164006-6407194 as the first ultracool member of the outer halo, expanding understanding of low-metallicity subdwarfs in this galactic component.

Findings

Spectral features indicate a cool, metal-poor atmosphere.

High proper motion and radial velocity suggest outer halo membership.

Kinematic analysis confirms its classification as an outer halo subdwarf.

Abstract

We present the serendipitous discovery of an L subdwarf, 2MASS J06164006-6407194, in a search of the Two Micron All Sky Survey for T dwarfs. Its spectrum exhibits features indicative of both a cool and metal poor atmosphere including a heavily pressured-broadened K I resonant doublet, Cs I and Rb I lines, molecular bands of CaH, TiO, CrH, FeH, and H2O, and enhanced collision induced absorption of H2. We assign 2MASS 0616-6407 a spectral type of sdL5 based on a comparison of its red optical spectrum to that of near solar-metallicity L dwarfs. Its high proper motion (mu =1.405+-0.008 arcsec yr-1), large radial velocity (Vrad = 454+-15 km s-1), estimated uvw velocities (94, -573, 125) km s-1 and Galactic orbit with an apogalacticon at ~29 kpc are indicative of membership in the outer halo making 2MASS 0616-6407 the first ultracool member of this population.