How does lower metal content in globular cluster stars affect isochrone application?

The specific model tracks must be meticulously adjusted for the precise metallicity before age determination.

Stellar age determination, particularly when using theoretical isochrones, is fundamentally dependent on knowing the initial chemical composition, often summarized by metallicity (the abundance of elements heavier than helium). When comparing a younger open cluster to an ancient globular cluster, the older globular cluster stars characteristically exhibit significantly lower metal content. Since the input physics used for theoretical models must accurately reflect the initial starting conditions of the stellar material, the standard isochrones developed for solar-composition stars cannot be directly applied. Therefore, astronomers must meticulously adjust the theoretical model tracks to account for this lower initial metallicity before the star's current position on the H-R diagram can reliably map back to an accurate elapsed time.