5 Conclusions

In this paper we have presented new integrated colours as computed for simple stellar population adopting a fully homogeneous set of evolutionary computations covering all the major evolutionary phases of globular cluster stars. We find that, adopting Reimers parameterization of mass loss rate, the choice $\eta =0.4$ appears in satisfactory agreement with the distribution of globular cluster stars in the CM diagram. We present theoretical predictions concerning U-B, B-V, V-R and V-I colours for selected assumption about the cluster metallicity in the range Z=0.0001 to 0.02 and for ages between 8 and 15 Gyr, finding that for an age t=15 Gyr all the predicted colours appear in good agreement with available data for both galactic and LMC old globulars.

Figure 9: Observed integrated colours of galactic globular clusters (Harris 1999) are compared to models ($\eta =0.4$) with different labelled age

We discuss the uncertainties of integrated colour due to statistical fluctuations in the number of luminous stars, giving for each colour the predicted uncertainty as a function of the cluster integrated V-magnitude. We finally show that reasonable uncertainties either in the cluster age or in the efficiency of mass loss have marginal effects on the predicted colours of such old SSPs.

Acknowledgements

We thank G. Piotto for kindly providing us with the photometric data. This work is supported by the Italian Ministry of University, Scientific Research and Technology (MURST): Cofin1998-Project: Stellar Evolution.