# # Program information file # PROGRAM_ID 2021B111 PROGRAM_TITLE The Mass Function of the Galactic Halo Down to the Hydrogen Burning Mass Limit PROGRAM_INV1 Adam Burgasser PROGRAM_INV2 Nicolas Lodieu PROGRAM_INV3 Christian Aganze PROGRAM_INV4 Enrique Solano PROGRAM_INV5 Eduardo Martin PROGRAM_SCICAT stellar PROGRAM_ABSTRACT_BEG The Galactic halo encompasses the oldest and most metal-depleted stars in the Milky Way system. The distinct abundances and [early] star formation conditions of this population allows us to investigate the role of metallicity and environment on the star formation process. This is particularly important for the lowest-mass stars, for which the lowest hydrogen burning mass is itself metallicity-dependent. In this study we aim to obtain classifying spectra of 66 newly uncovered late-M and L subdwarfs identified in a comprehensive search combining the Vista Hemisphere Survey and PanSTARRS surveys. By comparing the relative distribution of these sources to predictions of population synthesis models integrating metallicity effects, we aim to distinguish between competing models of the halo mass function, and search for evidence of a density decline at the latest subtypes indicative of the hydrogen fusion threshold. PROGRAM_ABSTRACT_END