Colloquium at CSU Long Beach: Searching for Lithium in L Subdwarfs
Channel: Adam Burgasser
Date: 2015-03-16

Local Probes of the Early Universe: Using Nearby Brown Dwarfs to Measure Lithium Production in Big Bang Nucleosynthesis

Brown dwarfs are stars of such low mass (less than 7% Msun) that they are incapable of sustained hydrogen fusion.  Below 6% of a Solar Mass, they are also incapable of lithium fusion. As lithium is fully mixed in the fully convective interiors of low-mass stars and brown dwarfs, the 670.8 nm Li I line has been used to identify substellar objects and as a nuclear “clock" for age-dating nearby clusters. Lithium is also relevant for understanding the early evolution of the Universe, and Big Bang Nucleosynthesis models currently overestimate the 7Li abundances measured in hot halo stars.  Since stellar evolution and structural effects play major roles in the observed elemental abundances of these stars, halo brown dwarfs potentially provide a more robust measure of the primordial lithium abundance.  In this talk, I describe a sensitive search for Li I in two of the brightest and coolest L-type subdwarfs with halo kinematics using the GTC and VLT. Neither source exhibits Li I absorption, indicating that they are stars that have depleted their lithium through fusion. I discuss the implications of these non-detections and their relevance to future prospects for probing primordial lithium abundances using brown dwarfs.