Observational Status of the Relic Abundances

On the basis of our discussion of the post-BBN evolution of D/H, it would be expected that there should be a Deuterium Plateau at high redshift. If, indeed, one is present, the dispersion in the limited set of current data hide it. Alternatively, to explore the possibility that the D-abundances may be correlated with the metallicity of the QSOALS, we may plot the observed D/H versus the metallicity, as measured by [Si/H], for these absorbers. This is shown in Fig. 4 where there is some evidence for an (unexpected ) increase in D/H with decreasing [Si/H] once again, the dispersion in D/H hides any plateau. 

Aside from studies of meteorites and in samples of the lunar soil (Reeves et al. 1973, Geiss Gloeckler 1998, Gloeckler Geiss 2000), 3He is only observed via its hyperfine line (of singly-ionized 3He) in interstellar Hu regions in the Galaxy. It is, therefore, 

The good news is that the data reveal a well-defined primordial abundance for 4He. The bad news is that the scale of Fig. 6 hides the very small statistical errors, along with a dichotomy between the OS/OSS and ITL/IT primordial helium abundance determinations (Yp(OS) = 0.234 0.003 versus Yp(IT) = 0.244 0.002). Furthermore, even if one adopts the IT/ITL data, there are corrections which should be applied which change 

It seems clear that until new data address the unresolved systematic errors afflicting the derivation of the primordial helium abundance, the true errors must be much larger than the statistical uncertainties. For the comparisons between the predictions of SBBN and the observational data to be made in the next section, I will adopt the Olive, Steigman Walker (2000 OSW) compromise Yp = 0.238 0.005 the inflated errors are an attempt to account for the poorly-constrained systematic uncertaintiess. 

As with the other relic nuclides, the dominant uncertainties in estimating the primordial abundance of 7Li are not statistical, they are systematic. Lithium is observed in the atmospheres of cool stars (see Lambert (2001) in these lectures). It is the metal-poor, Pop II halo stars that are of direct relevance for the BBN abundance of 7Li. Uncertainties in the lithium equivalent width measurements, in the temperature scales for 

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