THE LEVEL OF AGREEMENT BETWEEN THEORETICAL AND OBSERVED GLOBULAR-CLUSTER LUMINOSITY FUNCTIONS

Luminosity functions from theoretical stellar evolution calculations a re compared with observed ones of several galactic globular clusters ( M30, M92, M68, NGC6397, M4, M80, NGC6352, NGC1851). Contrary to earlie r results of Faulkner & Swenson (1993) and Bolte (1994) we find no sig nificant discrepancy that could indicate the neglect of important phys ical effects in the models. However, it is confirmed that the subgiant branch is the most sensitive part and shows the largest deviations in the luminosity function comparison, if parameters are unappropriate. We also find that the main sequence is suited less than the Red Giant Branch for the calibration of theoretical luminosity functions, mainly because of apparent completeness problems. While for individual clust ers different changes in the model assumptions might resolve mismatche s, there is no systematic trend visible. It rather appears that the qu ality of the luminosity function in the subgiant part is insufficient and that improved observations of this particular region are necessary for a better comparison. At the present quality of luminosity functio ns theory is in agreement with observations and a postulation of WIMPs acting in stellar cores does not seem to be justified. However, we co nclude that improved data for the main sequence and subgiant branch ar e clearly needed to exploit the potential of luminosity functions as a diagnostic means for stellar evolution theory.