Lithium Depletion Boundary in a Pre-Main-Sequence Binary System

A lithium depletion boundary is detected in HIP 112312 (GJ 871.1 A and B), an ~12 Myr old pre-main-sequence binary system. A strong (EW ≈ 300 mÅ) Li λ6708 absorption feature is seen in the secondary (~M4.5), while no Li λ6708 feature is detected in the primary (~M4). The physical companionship of the two stars is confirmed by their common proper motions. Current theoretical pre-main-sequence evolutionary models cannot simultaneously match the observed colors, brightnesses, and Li depletion patterns of this binary system. At the age upper limit of 20 Myr, contemporary theoretical evolutionary models predict a too slow Li depletion. If true Li depletion is a faster process than predicted by theoretical models, the ages of open clusters (Pleiades, α Persei, and IC 2391) estimated from the Li depletion boundary method are all overestimated. Because of the importance of the open cluster age scale, development of self-consistent theoretical models to match the HIP 112312 data is desirable.