Astron. Astrophys. 324, 65-79 (1997)

5. Conclusions and future work

We studied the colour distribution towards the galactic poles and anti-centre. The analysis shows that the distributions are well reproduced by the sum of four stellar populations in the disc: a young, intermediate, old, and thick disc population.

In the spheroid two major populations are distinguished: a metal poor halo population and a metal richer 'bulge' population. The presence of the latter could not be well constrained from the north galactic pole observations. Both the halo and the bulge are well described by a power-law with index n = 3.0 . Furthermore, the spheroid appears not to be flattened or the flattening is very small (0.95 1.00) .

There are still some discrepancies present between the model and the observed colour distributions. These discrepancies are related with the decrease of the slope of the power-law IMF for stars with M/ 1.0 and the age of the thick disc stars. They might bias the local normalization. Therefore, the IMF will be the subject for future research, where the lower mass limit in the HRD-GST library of stellar evolutionary tracks is extended downwards to 0.15  . With an improved galactic model the HRD-GST might be able to obtain better constraints for the bulge population and to distinguish between stellar populations from a hierarchical formation process or those from a merger event.

© European Southern Observatory (ESO) 1997

Online publication: May 26, 1998

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