Lithium Depletion Boundary in Brown Dwarfs

Lithium-7 is destroyed by proton capture at core temperatures far below those needed for hydrogen fusion, so it works as a sharp thermometer for the coolest stars and brown dwarfs. This simulation models a coeval population of 44 low-mass objects spanning 0.02–0.16 solar masses, each contracting under a simplified Kelvin–Helmholtz heating law, and tracks whether each one's core has crossed the lithium-ignition temperature at the current cluster age. Scrub the age slider (or hit Play) to watch the lithium depletion boundary — the sharp mass cutoff between lithium-rich and lithium-depleted objects — sweep down to lower mass as the cluster ages, exactly the effect astronomers use to date young star clusters independently of isochrone fitting. Adjust the ignition-temperature and contraction-rate parameters to see how modelling uncertainty shifts the boundary mass.