Figure 3.2 shows our results for silicon and titanium. The thin- and thick-disk membership can easily be decided from these plots. The offset from [Si/Fe] = 0 at [Fe/H] = 0 found in several previous surveys is not apparent in the left-hand panels
1 rJttfr J
I : .. 1 ...,...,. ■
Figure 3.2. Abundances of Si and Ti, and their ratios to the iron abundances for the sample stars. The broken lines mark the location of the Solar reference values.
of Figure 3.2. Similarly, the right-hand panels do not confirm the offset found by Allende Prieto et al. (2004) for titanium, and no significant offsets were found for carbon, calcium, titanium, and nickel either. This result suggests that the offsets in previous analyses were likely the result of systematic errors.
Samples of stars spanning a narrow range in atmospheric parameters are well suited for carrying out differential studies of chemical evolution. With such samples, we can potentially minimize the impact of shortcomings in the theory of stellar atmospheres and line formation on the derived abundances, as the small scatter in the abundance ratios shown in Figure 3.2 suggests.
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