Oxygen solar abundance

Results for the Simple model are shown in Fig. 9.5. Oxygen abundance simply increases in proportion to u, whereas that of 7Li starts from a finite base and tends to a limiting value p].,/(a l — 1) owing to its eventual destruction by astration. Deuterium (p = 0 in Eq. 9.25) suffers little destruction as long as the oxygen abundance (or metallicity) is less than about 0.1 of the true yield (assumed to be comparable to solar abundance), e.g. in high-redshift absorption-line clouds, but... 

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... 

To illustrate how a (simple) condensation calculation works, let s consider the condensation of corundum (Al203), one of the earliest phases predicted to condense from a solar gas. The partial pressures of aluminum (PAi) and oxygen (P0) in the gas phase must first be determined, based on their solar abundances, over a range of temperatures. The eguilibrium between solid (s) corundum and gas (g) can be represented by this equation ... 

Natural isotopes of oxygen and their solar abundances... 

Figure 3 Element/Si mass ratios of characteristic elements in various groups of chondritic (undifferentiated) meteorites. Meteorite groups are arranged according to decreasing oxygen content. The best match between solar abundances and meteoritic abundances is with Cl meteorites (see text for details).

Updated solar photospheric abundances are compared with meteoritic abundances. It is shown that only one group of chondritic meteorites, the Cl chondrites, matches solar abundances in refractory lithophile, siderophile, and volatile elements. All other chondritic meteorites differ from Cl chondrites. The agreement between solar and Cl abundances for all elements heavier than oxygen and excluding rare gases has constantly improved since Goldschmidt (1938) published his first comprehensive table of cosmic abundances. 

Oxygen isotope abundance variations in meteorites are very useful in elucidating chemical and physical processes that occurred during the formation of the solar system (Clayton, 1993). On Earth, the mean abundances of the three stable isotopes are 99.76%, 0.039%, and... 

Johnston (1929) refer to nonuniform distribution of oxygen isotopes as a remote possibility, whereas Manian et al. (1934) sought to find variations in oxygen isotope abundances in meteorites as evidence for an origin outside the solar system. 

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. 

Figure 27. Oxygen abundance from the R23 = ([O II]+[0 111]) /11/5 ratio. In each panel the continuous lines are the calibration by McGaugh (1991) for the ionisation index 032 = [O III]/[0 II] appropriate to that object. The shaded area shows the values allowed by the measured U23 and its statistical 1

The key processes for the formation of the simplest carbon-, oxygen- and nitrogenbearing molecules have been discussed extensively before (Dalg2imo iuid Bktck 1976 Watson 1978 Crutcher itnd Watson 1985 vein Dishoeck 1988), emd will be only briefly reiterated here. Since H and are so much more abundemt in interstellar clouds than any other species, the dominant reactions usually involve hydrogen, whenever possible. Table 2 lists the current best estimates of the solar abundances of the veirious elements relative to hydrogen. Some of the heavier elements are depleted from the gas phase in interstellar clouds. In diffuse clouds, this depletion is very mild and tends to exceed a feictor of four only for heavier metals like Ca, Ti, Mn, emd Fe. The freiction of the solar abundemce of element X in the gas phase is denoted by the depletion foctor Sx, with Sx < 1-... 

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