In traditional spectroscopic analyses of metal-poor stars, the mean abundance ratio of the chemical elements is discussed as a function of the overall metallicity, usually measured by the iron abundance [Fe/H]. The results are then compared to predictions from models of nucleosynthesis and chemical evolution of the Galaxy, and they are used to provide constraints on the sites and mechanisms for element synthesis. Unfortunately, these abundance ratios show rather considerable star-to-star scatter, therefore providing only weak constraints on the models.
With the improvement of observing and spectroscopic analysis techniques, it is now possible to reduce considerably the observational uncertainties in the abundance determinations, therefore decreasing the scatter in the abundance ratios. If the data are of sufficient quality, the remaining scatter is then mostly a genuine cosmic scatter which can be measured and analysed. We can investigate the cosmic scatter in relative abundances at a given metallicity and identify abundance correlations between several elements. Since the elements which are strongly correlated together have very likely been synthesized by the same nucleosynthetic processes in the same kinds of objects, we now have a new and efficient tool for identifying the sites and mechanisms of element synthesis at different stages of the galactic evolution. This new tool leads us to propose a scenario for the formation of field halo stars which links them to the globular clusters evolution.
© European Southern Observatory (ESO) 1998
Online publication: January 16, 1998