Age Estimation Using H β Index 3

After taking into account, for the first time, the detailed systematic variation of horizontal-branch (HB) morphology with age and metallicity, our population synthesis models show that the integrated Hβ index is significantly affected by the presence of blue HB stars. Our models indicate that the strength of the Hβ index increases as much as 0.75 Å due to blue HB stars. According to our models, a systematic difference between the globular cluster system in the Milky Way Galaxy and that in NGC 1399 in the Hβ vs. Mg2 diagram is understood if globular cluster systems in giant elliptical galaxies are couple of billion years older, in the mean, than the Galactic counterpart.