Theoretical Examination of the Lithium Depletion Boundary

Abstract

We explore the sensitivity in open cluster ages obtained by the lithium depletion boundary (LDB) technique to the stellar model input physics. The LDB age technique is limited to open clusters with ages ranging from 20 to 200 Myr. Effective 1-sig errors in the LDB technique due to uncertain input physics are roughly 3% at the oldest age increasing to 8% at the youngest age. Bolometric correction uncertainties add an additional 10 to 6% error to the LDB age technique for old and young clusters, respectively. Rotation rates matching the observed fastest rotators in the Pleiades affect LDB ages by less than 2%. The range of rotation rates in an open cluster are expected to ``smear'' the LDB location by only 0.02 mag for a Pleiades age cluster increasing to 0.06 mag for a 20 Myr cluster. Thus, the observational error of locating the LDB (~7-10%) and the bolometric correction uncertainty currently dominate the error in LDB ages. For our base case, we formally derive a LDB age of 148 +- 19 Myr for the Pleiades, where the error includes 8, 3, and 9% contributions from observational, theoretical, and bolometric correction sources, respectively. A maximally plausible 0.3 magnitude shift in the I-band bolometric correction to reconcile main sequence isochrone fits with the observed (V-I) color for the low mass Pleiades members results in an age of 126 +- 11 Myr, where the error includes observational and theoretical errors only. Upper main-sequence-fitting ages that do not include convective core overshoot for the Pleiades (~75 Myr) are ruled out by the LDB age technique.