Can Larger M-star Radii Reconcile Li-depletion and HR Diagram Ages for Young Stars?

Details Can Larger M-star Radii Reconcile Li-depletion and HR Diagram Ages for Young Stars? Can Larger M-star Radii Reconcile Li-depletion and HR Diagram Ages for Young Stars?

Jan 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21538206j&link_type=abstract

American Astronomical Society, AAS Meeting #215, #382.06; Bulletin of the American Astronomical Society, Vol. 42, p.593

Astronomy and Astrophysics

Astronomy

Scientific paper

Determining accurate ages for young field stars can help identify interesting targets for studying planet formation and stellar evolution. Two leading ways of finding a young star's age are from its HR diagram position or from its level of Li depletion. In both cases, these observations must be compared with theoretical evolutionary models to determine an age. However, a number of observations have shown that ages determined from Li depletion tend to be older than those determined from the HR diagram, particularly for M stars. Here we present high-resolution spectroscopy of the K and M stars in the nearby (d < 50 pc) Beta Pic Moving Group, showing that current models systematically underpredict the level of Li depletion for the M stars in this 10-Myr-old group. We also suggest that recent observations showing that active main-sequence M stars have radii 10-20 percent larger than predicted by models are relevant to understanding pre-main-sequence ages. If these pre-main-sequence stars also have radii larger than those in the models, the effect of correcting the models should be to decrease the Li depletion ages and increase the HR diagram ages, bringing them into closer agreement, and possibly also reducing the discrepancies between HR diagram ages of cooler and warmer stars in a given group.
This work was supported by NSF grant AST-0307830.

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