Chemical evolution elements

The term chemical evolution" was introduced by the Nobel Prize winner Melvin Calvin and refers to the process of the synthesis of biochemically important molecules from small molecules and certain chemical elements under the (hypothetical) conditions present on prebiotic Earth. It is assumed that the smaller building block molecules such as amino acids, fatty acids or nucleobases were formed initially, and that these underwent polycondensation to give macromolecules in later stages of development. 

The studies of other elements in metal-rich planet-host stars is also giving important information about the chemical evolution of the Galaxy. 

Recent observations of the HF (1-0) R9 line at 2.3 /tm with the Phoenix spectrograph on the Gemini-South telescope has opened a new window that sheds light on understanding the chemical evolution of fluorine and the nuclear processes that produce this element. Until recently, only a small number of observations of fluorine were available and the trend of fluorine abundances with metallicity had yet to be probed in the Galaxy. 

Abstract. The most recently discovered Galactic component - thick disk - still needs high-resolution spectral investigations since its origin and evolution is not understood enough. Elemental abundance ratios in the metallicity range —0.68 < [Fe/H] < —0.10 were determined in a sample of 10 thick-disk dwarfs and compared with results of other stars investigated as well as with models of thin disk chemical evolution. 

Studies of chemical abundances of metal rich samples are still not numerous due to the paucity of stars in the super-solar metallicity range. Nevertheless, some recent works have succeeded to delineate the chemical evolution pattern of important elements, showing interesting behaviors for such domain (e.g. [2], [6]). In the present work we report preliminary abundances for super-solar metallicity bulge-like stars. 

Recent abundance ratio work in this field falls into two categories. The first category has been investigations into aspects of metal-poor AGB and Type la SN yields and their relationship to the chemical evolution in the dSph galaxies, e.g. McWilliam et al. (2003), Venn et al. (2004), McWilliam Smecker-Hane (2005). In these works the abundances of specific elements are compared to... 

Abstract. Observed large scatters in abundances of neutron-capture elements in metal-poor stars suggest that they are enriched a single or a few supernovae. Comparing predictions by an inhomogeneous chemical evolution model and new observational results with Subaru HDS, we attempt to constrain the origins of r-process elements. 

Although Ba and heavier elements seem to fit the solar r-process pattern, lighter elements show wide varieties [5]. In particular, a large dispersion has been found in [Sr/Ba] at low metallicity[l], suggesting that lighter elements such as Sr does not come from a universal process, which produces Ba and Eu, but from weak r-process. An inhomogeneous chemical evolution model suggests that the dispersions in [Sr/Ba] are well-explained, when weak r-process produces 60% of Sr but only 1% of Ba in metal-poor stars. Furthermore, intermediate mass elements such as Pd must provide clues to understand the weak r-process yield. 

Our chemical evolution model for the MW predicts [4] that the abundance gradients for different elements were almost flat in the very early phases of the thin disk formation (Fig. 2). Moreover we predict little evolution of the abundance gradients in the last 5 to 8 Gyrs. 

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... 

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... 

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... 

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

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