GLOBULAR-CLUSTER ISOCHRONES IN THE INFRARED

Synthetic infrared colours have been used to transform globular cluster isochrones to the (M(K), V - K), (M(V), V - K) and (M(K), J - K) planes. A comparison with an observed (M(V), V - K) colour-magnitude diagram for 47 Tuc indicates an age consistent with that of 13.5 Gyr found from the (M(V), B - V) diagram. The relative positions of the giant branches in the (M(K), J - K) and (M(V), V - K) planes at M(K) = - 5.5 have been tested as a function of metal abundance by comparison with empirical calibrations. The fit is satisfactory when allowance is made for zero-point corrections in the computed colours.