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When determining absolute ages of identifiably young stellar populations,results strongly depend on which stars are studied. Cooler (K, M) starstypically yield ages that are systematically younger than warmer (A, F, G)stars by a factor of two. I explore the possibility that these agediscrepancies are the result of magnetic inhibition of convection in cool youngstars by using magnetic stellar evolution isochrones to determine the age ofthe Upper Scorpius subgroup of the Scorpius-Centaurus OB Association. A medianage of 10 Myr consistent across spectral types A through M is found, except fora subset of F-type stars that appear significantly older. Agreement is shownfor ages derived from the Hertzsprung-Russell diagram and from the empiricalmass-radius relationship defined by eclipsing multiple-star systems. Surfacemagnetic field strengths required to produce agreement are of order 2.5 kG andare predicted from a priori estimates of equipartition values. A region in theHR diagram is identified that plausibly connects stars whose structures areweakly influenced by the presence of magnetic fields with those whosestructures are strongly influenced by magnetic fields. The models suggest thisregion is characterized by stars with rapidly thinning outer convectiveenvelopes where the radiative core mass is greater than 75% of the totalstellar mass. Furthermore, depletion of lithium predicted from magnetic modelsappears in better agreement with observed lithium equivalent widths thanpredictions from non-magnetic models. These results suggest that magneticinhibition of convection plays an important role in the early evolution oflow-mass stars and that it may be responsible for noted age discrepancies inyoung stellar populations.

astronomy and astrophysics

Magnetic Inhibition of Convection and the Fundamental Properties of  Low-Mass Stars. III. A Consistent 10 Myr Age for the Upper Scorpius OB  Association