Models for the Galactic halo and disk

Numerical modelling of the chemical evolution of the Milky Way and/or similar disk galaxies, taking into account dynamical effects, was pioneered by Larson (1976) and Tinsley and Larson (1978). Because of many uncertainties in the details 

Some specific GCE models and related observational data 

The behaviour of elements like Ba, which have an s-process contribution at least in the case of the more metal-rich stars, may require two components one with a short time delay as assumed by Pagel (1989a) and another one with a time delay slightly exceeding that for SN la (Edvardsson et al. 1993 Pagel Tautvaisiene 1997) see Fig. 8.30. 

Some further developments in analytical modelling are described in Section 8.6.4. 

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Models for the Galactic halo and disk Table 8.3. Some parameters of the mixing modela... 

The resulting dependences of [Th/Eu] on stellar age are shown in Fig. 10.5, together with a selection of observational data from del Peloso et al. for disk stars Westin et al. (2000) for two of the r-process enriched ultra-metal-poor (UMP) halo stars and Cowan et al. (2002) for a third one. The range among disk stars is little more than can be expected from uncertainties in the determination, while the UMP stars show more or less the expected deficiency. For BD +17 0 3248, Cowan et al. used theoretical production ratios for Th relative to Eu, Ir and Pt, based on certain nuclear models, to deduce a Galactic-model-independent age of 13.8 4 Gyr, which happens to fit our two production-ratio-independent model curves simple inflow and modFowler T = 15 quite nicely, but the error bars are large so that what we have is more a test of consistency than an independent chronometer. 

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