Nitrogen solar abundance

SNII events alone explain the observed solar abundance distribution between oxygen and chromium. This can be taken as a major theoretical achievement. Complementary sources of hydrogen, helium, lithium, beryllium, boron, carbon and nitrogen are required, and these have been identified. They are the Big Bang, cosmic rays and intermediate-mass stars. Around iron and a little beyond, we must invoke a contribution from type la supernovas (Pig. 8.5). These must be included to reproduce the evolution of iron abundances, a fact which suggests... 

Finally, we mention the central star of NGC 246. This star is known to display CIV as the strongest absorptions in the blue spectrum and broad shallow lines of Hell hydrogen can not be detected (Heap, 1975 Husfeld, 1986). Analysis by Husfeld (1986) revealed that this CSPN is extremely hydrogen-deficient solar abundance of this element cannot be excluded. 

Natural isotopes of nitrogen and their solar abundances... 

Because nitrogen possesses only two stable isotopes, it is a matter of semantics to assert which isotope is varying in meteoritic presolar-grain samples that have different isotope ratios (see 14N for that data in presolar grains). Identifying the correct solar abundance ratio for N, whether terrestrial or Jovian (see Abundance, above) will facilitate interpretation of yet other ratios found in presolar grains. 

The observational constraints on the solar isotopic abundances of oxygen are also poor. The only solar-wind measurement, by the Advanced Composition Explorer, yielded a ratio of consistent with the terrestrial value, with 20% uncertainty (Wimmer-Schweingruber et al., 2001). An earlier spectroscopic measurement of the solar photosphere gave a similar result (Harris et al., 1987). No information is available on the solar abundance. The very limited state of knowledge of the solar isotope abundances of carbon, nitrogen, and oxygen illustrates the importance of the NASA Genesis mission to collect a pure solar-wind sample and return it to Earth for laboratory measurement. 

Noble gases and nitrogen in martian meteorites reveal several interior components having isotopic compositions different from those of the atmosphere. Xenon, krypton, and probably argon in the mantle components have solar isotopic compositions, rather than those measured in chondrites. However, ratios of these noble gas abundances are strongly fractionated relative to solar abundances. This decoupling of elemental and isotopic fractionation is not understood. The interior ratio in martian meteorites is similar to chondrites. 

Figure 2. Nitrogen isotope abundances in solar system materials upper scale gives absolute ratios lower scale gives relative to the terrestrial AIR standard. Heavy bars show observed ranges light bars show measurement...

As evidenced by their low abundances, carbon compounds, water, and other volatiles such as nitrogen compounds were probably not significantly abundant constituents of the bulk of the solids that formed near the Earth. Many of the carriers of these volatiles condensed in cooler, more distant regions and were then scattered into the region where the Earth was forming. Eragments of comets and asteroids formed in the outer solar system still fall to Earth at a rate of 1 x 10 kg/yr and early in the... 

The volatile-trapping mechanism has a further problem associated with the temperature. Very volatile molecules such as N2, CO and CH4 are not easily trapped in laboratory ice simulation experiments unless the ice temperature is 75 K, which is somewhat lower than the estimated Saturnian subnebula temperature. This has led to the suggestion that the primary source of nitrogen within the Titan surface ices was NH3, which became rapidly photolysed to produce H2 and N2 upon release from the ice. The surface gravity is insufficient to trap the H2 formed and this would be lost to space. However, the origin of methane on Titan is an interesting question. Methane is a minor component of comets, with a CH4/CO ratio of clCT1 compared with the present atmospheric ratio of > 102. The D/H ratio is also intermediate between that of comets and the solar nebula, so there must be an alternative source of methane that maintains the carbon isotope ratio and the D/H isotope ratio and explains the abundance on Titan. 

By studying radio and optical spectra from HII regions and planetary nebulas, to be discussed immediately below, we may establish the abundances of several elements, in particular, helium, absent from the solar spectrum, a point of great cosmological significance, but also nitrogen and oxygen. 

Third, carbon, nitrogen, and oxygen, the elements that catalyze hydrogen burning in the Sun, are relatively abundant in the solar system. Oxygen is somewhat more abundant than carbon the C/O ratio is 0.54. Because CO is a very stable molecule, most of the carbon and oxygen in the early solar system was tied up in CO. The excess oxygen that remained controlled the chemical environment of the early solar system. 

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