We present the results of a spectroscopic survey of X-ray selected , low-mass candidate members of the young open cluster NGC 2547 .
Using a combination of photometry , spectroscopic indices and radial velocities we refine our candidate list and then use our spectroscopy to study the progression of lithium depletion in low-mass pre main sequence stars .
We derive lithium abundances or upper limits for all our candidate members , which have effective temperatures in the range 5000 > T _ { eff } > 3200 K , and compare these with predictions for lithium burning and depletion provided by a number of models and also with the lithium depletion seen in younger and older stars .
We find that some models can reproduce the lithium abundance pattern of NGC 2547 if the cluster has an age of \simeq 20 - 35 Myr , which is also indicated by fits to low-mass isochrones in the Hertzsprung-Russell diagram .
But the lack of significant further lithium depletion between NGC 2547 and older clusters argues for an age of at least 50 Myr , more in keeping with the lack of lithium observed in even fainter NGC 2547 candidates .
We show that reconciliation of these age estimates may require additions to the physics incorporated in current generations of pre main sequence models .