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Astron. Astrophys. 319, 487-497 (1997)

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The level of agreement between theoretical and observed globular cluster luminosity functions

S. Degl'Innocenti 1, 2, A. Weiss 1 and L. Leone 3

1 Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, D-85748 Garching, Germany
2 INFN Sezione di Ferrara, I-44100 Ferrara, Italy
3 Dipartimento di Fisica, Università di Pisa, Piazza Torricelli 2, I-56100 Pisa, Italy

Received 13 February 1996 / Accepted 1 August 1996


Luminosity functions from theoretical stellar evolution calculations are compared with observed ones of several galactic globular clusters (M30, M92, M68, NGC6397, M4, M80, NGC6352, NGC1851). Contrary to earlier results of Faulkner & Swenson (1993) and Bolte (1994) we find no significant discrepancy that could indicate the neglect of important physical 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 clusters different changes in the model assumptions might resolve mismatches, there is no systematic trend visible. It rather appears that the quality 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 functions theory is in agreement with observations and a postulation of WIMPs acting in stellar cores does not seem to be justified. However, we conclude that improved data for the main sequence and subgiant branch are clearly needed to exploit the potential of luminosity functions as a diagnostic means for stellar evolution theory.

Key words: stars: evolution – stars: luminosity function – globular clusters: general

Send offprint requests to: A. Weiss; (weiss@mpa-garching.mpg.de)

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© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998