Cosmic abundances of elements

Cosmic abundances of elements and isotopes Table 3.3. Exponential curves of growth... 

In order to determine the absorption column Nn, the above model was fitted to the average spectra. As the result, the spectra A and B gave Nu-values both approximately equal to 102K H atoms/cm2 for the cosmic abundances of element. The spectrum C is insensitive to determine the N -value uniquely. However, we assume the same form of the hard component also during the January flare, because the hard component is likely to be independent of the soft component. We therefore fixed the Nn at 102S H atoms/cm2, and performed fitting to the spectrum C. The intensity of the hard component was dealt with as a free parameter. 

Although the elemental composition of the solar system is roughly similar to that of many other stars, in particular with respect to the relative abundances of the nongaseous elements, there are, in detail, compositional differences among stars and there are, in addition, truly exotic stars that make the term cosmic abundances of elements questionable. We will therefore use the term solar system abundances of the elements in this chapter. 

The chemical composition of ices in space is inferred theoretically on the basis of condensation theory, which predicts tlie composition of solids condensed from gas of Uie cosmic abundance of elements. In Table 9.2, chemical compositions of ices and corresponding equilibrium condensation temperatures are shown in protosolar nebula [1] and interstellar molecular clouds [2],... 

The cosmic abundance of elements forms a basis for considering the chemical composition of ice in space. The cosmic abundance of major elements is summarized in Table 9.1. The most abundant elements, H and He, are veiy volatile, and exist as gas in the tenuous environment in space. Elements heavier than H and He can form solids. The elements C, N, and O combine with H to form ices at temperatures lower than about 100K, and Si, Mg, and Fe combine with O to form silicates, metals, and their oxides. Note that the elements that form ices are much more abundant than tlie elements that form silicates and metals. 

Fig. 9. Cosmic abundance of elements compared with silicon (10 ) (Suess and Urey).

Fig. 1.1 The cosmic abundance of elements. The relative abundance of elements (vertical axis) is defined as the number of atoms of each element per 106 atoms of silicon and is plotted on a logarithmic scale.

FIGURE 2.1. Cosmic abundance of elements as a function of atomic number Z [2.4], Abundances are expressed as numbers of atoms per 10 atoms of Si and are plotted on i logarithmic scale. 

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