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Astron. Astrophys. 341, L71-L74 (1999)

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5. Conclusions

The results shown by Fig. 2 are not in agreement with the predictions from theoretical models of stellar evolution. However, the general trends are very similar, only more pronounced in the observations: an increase in brightness already on the main sequence seems to start earlier than expected. From an observational point of view, one of the conclusions has to be that distance estimates for young star clusters have been over estimated. Among such estimates are distance determinations to the LMC and to OB associations. De Zeeuw et al. (1999) find for OB associations (spread over much larger parts of the sky than most open clusters) also distances which are generally less than what had been expected from ground-based observations.

What the consequences may be for absolute age estimates obtained from theoretical isochrones is far beyond the scope of this note. However, an unresolved difference between observations and theory as presented here inevitably introduces a degree of uncertainty in any such estimates. Differential age estimates as used in the present paper are unlikely to be affected.

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© European Southern Observatory (ESO) 1999

Online publication: December 16, 1998