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    The Lithium Depletion Boundary and the Age of the Young Open Cluster IC~2391

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    We have obtained new photometry and intermediate resolution (Δλ=2.7\Delta \lambda = 2.7 \AA\ ) spectra of 19 of these objects (14.9 ≤\le IcI_c ≤\le 17.5) in order to confirm cluster membership. We identify 15 of our targets as likely cluster members based on their VRIVRI photometry, spectral types, radial velocity, and Hα\alpha emission strengths. Higher S/N spectra were obtained for 8 of these probable cluster members in order to measure the strength of the lithium 6708 \AA\ doublet and thus obtain an estimate of the cluster's age. One of these 8 stars has a definite lithium detection and two other (fainter) stars have possible lithium detections. A color-magnitude diagram for our program objects shows that the lithium depletion boundary in IC~2391 is at IcI_c=16.2. Using recent theoretical model predictions, we derive an age for IC~2391 of 53±\pm5 Myr. While this is considerably older than the age most commonly attributed for this cluster (∼\sim35 Myr) this result for IC~2391 is comparable those recently derived for the Pleiades and Alpha Persei clusters and can be explained by new models for high mass stars that incorporate a modest amount of convective core overshooting.Comment: ApJ Letters, acccepte
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