Theoretical stellar luminosity functions and the ages and compositions of globular clusters

Using recently calculated tables (Los Alamos) of radiative opacities and the latest thermonuclear reaction rates, stellar evolutionary tracks for low-mass (0. 4 - 1. 2 Mₛun;) Population II stars (0. 0001 ≤ Z ≤ 0. 01) have been calculated for two helium abundances, Y = 0. 2 and 0. 3. Luminosity functions (LFs) for ages 8 Gyr ≤ t ≤ 20 Gyr have been constructed from these tracks, and the resultant dependence of LF morphologies on age and chemical composition has been studied. The observed M13 LF has been compared to these theortical LFs. Assuming a distance modulus of (m-M) 0= 14. 3, a metallicity-independent lower bound of 14 Gyr can be placed on the age of M13.