Galactic chemical evolution

The general expectation is that secondary isotopes, such as 170,180, 29Si, 30Si, and 46Ti, 

and 50Ti increase in relative abundance compared to primary isotopes, such as 160, 28Si, and 48Ti, with time and overall metallicity in the universe (Chapter 3). The first 

Titanium isotopic data for mainstream silicon carbide grains versus 829Si. The correlation between excesses of minor titanium isotopes and minor silicon isotopes most likely reflects galactic chemical evolution. The offset of the S50Ti trend to pass above the solar composition probably reflects 5-process nucleosynthesis in the parent stars, which most strongly affects 50Ti. Data from Huss and Smith (2007) and references therein. 

The discussions above show that presolar grains can give considerable information on galactic chemical evolution. However, the theoretical framework within which to interpret that information is not as mature at that for stellar nucleosynthesis. This is an area with great promise for future work. 

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Theoretical models of galactic chemical evolution offer varying predictions of how the gradient should change with time, so using open clusters to measure that time-dependence can provide important constraints on model parameters. 

Old Open Clusters as Tracers of Galactic Chemical Evolution the BOCCE Project... 

Abstract. We recall the emergence of the 3He problem , its currently accepted solution, and we summarize the presently available constraints on models of stellar nucleosynthesis and studies of Galactic chemical evolution from observations of the He isotopic ratio in the Galaxy. 

Figure 1.1 also gives a schematic illustration of the complex interactions between the ISM and stars. Stars inject energy, recycled gas and nuclear reaction products ( ashes of nuclear burning ) enriching the ISM from which other generations of stars form later. This leads to an increase in the heavy-element content of both the ISM and newly formed stars the subject of galactic chemical evolution (GCE) is really all about these processes. On the other hand, nuclear products may... 

A. McWilliam, Abundance Ratios and Galactic Chemical Evolution , Ann. Rev. Astr Astrophys., 35, 503, 1997. 

Fig. 4.12. Stellar lithium abundances (log of the number per 1012 H atoms) among main-sequence stars as a function of metallicity. The full-drawn curve shows the prediction of a numerical Galactic chemical evolution model, while the broken-line curve gives the sum of a primordial component and an additional component proportional to iron and normalized to meteoritic abundance. Adapted from Matteucci, D Antona and Timmes (1995).

The site of the r-process is also not clear, but it seems that the conditions needed to reproduce Solar-System r-process abundances may hold in the hot bubble caused by neutrino winds in the immediate surroundings of a nascent neutron star in the early stages of a supernova explosion (see Fig. 6.10). Circumstantial evidence from Galactic chemical evolution supports an origin in low-mass Type II supernovae, maybe around 10 M (Mathews, Bazan Cowan 1992 Pagel Tautvaisiene 1995). Another possibility is the neutrino-driven wind from a neutron star formed by the accretion-induced collapse of a white dwarf in a binary system (Woosley Baron 1992) leading to a silent supernova (Nomoto 1986). In stars with extreme metal-deficiency, the heavy elements sometimes display an abundance pattern characteristic of the r-process with little or no contribution from the s-process, and the... 

Galactic chemical evolution basic concepts and issues... 

Galactic chemical evolution basic concepts and issues Table 7.1. Representative stellar data... 

Fig. 8.6. Variation of [Mg/Fe] with [Fe/H] in stars, after Bensby, Feltzing and Lundstrom (2003). The lower panel shows the converse plot of [Fe/Mg] vs. [Mg/H], which is more straightforwardly related to the progress of Galactic chemical evolution. Filled and open symbols represent stars of the thick and thin disks respectively.

The Galactic chemical evolution of heavy neutron-capture elements was studied by Travaglio et al. (1999, 2001) on the assumption that a small pocket of 13C is mixed into the inter-shell zone after the decay of each thermal pulse and generates neutrons supplemented by a small contribution from 22Ne during the next pulse see... 

For a description of additional numerical Galactic chemical evolution models, as well as aspects of nucleosynthesis (e.g. from novae) not discussed in this book, see the monograph by Matteucci (2001). 

Galactic chemical evolution of light elements Table 9.2. Results of simple calculations of light element abundances... 

Fig. 9.9. Galactic chemical evolution of 6Li, according to models with and without cosmological cosmic rays, the former providing a plateau at low metallicities. After Rollinde, Vangioni-Flam Olive (2005).

Short-lived activities and Galactic chemical evolution... 

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