Abundance Systematics

Osmium [74] found A(Os) = 1.25 0.11. This is significantly lower than the value of 1.45 0.10 used in previous compilations. Both Os values seem to be problematic when compared to the meteoritic value of 1.37 0.03. Assuming that the meteoritic value is reliable, the older photospheric value is 17% too low and the new one 30% too high. Grevesse et al. [16] selected the newer, smaller value but a conservative approach is to adopt the value with the smaller difference to the meteoritic value. The older value of A(Os) = 1.45 also appears more reasonable considering abundance systematics in the Pt-element region. Nucleosynthesis models predict that Os should be more... 

Relative noble gas abundance systematics of arc-related volcanism... 

It IS hard to find a class of compounds in which the common names of its members have influenced organic nomenclature more than carboxylic acids Not only are the common names of carboxylic acids themselves abundant and widely used but the names of many other compounds are derived from them Benzene took its name from benzoic acid and propane from propionic acid not the other way around The name butane comes from butyric acid present m rancid butter The common names of most aldehydes are derived from the common names of carboxylic acids—valeraldehyde from valeric acid for exam pie Many carboxylic acids are better known by common names than by their systematic ones and the framers of the lUPAC rules have taken a liberal view toward accepting these common names as permissible alternatives to the systematic ones Table 19 1 lists both common and systematic names for a number of important carboxylic acids... 

Figure 3. Systematics of radionuclides along the series. The major and minor fluxes to each nuclide can be readily seen from the arrows showm The behavior of each nuclide can be evaluated by considering the surface and groundwater populations individually, or together as the mobile pool. Nuclides in the decay series within the host rock minerals supply atoms at the surface and in the groundwater by recoil during a decay, so that there are greater abundances in the mobile pool of nuchdes progressively along the series, a decay of nuclides at the surface injects atoms back into the minerals as well as into groundwater.

Only recently have large numbers of open clusters become the subject of elemental abundance determinations other than those of the lightest elements (Li, C). A survey of the literature (not guaranteed to be complete), including some unpublished data kindly made available for this contribution, revealed [Fe/H] determinations for 45 open clusters. Of these, 33 have determinations of at least some of the a-elements, and these are collected in Table 1. There are very few clusters in common between studies, so it is not possible to investigate systematic differences between studies, nor to bring these measures to a common system. 

Working with clusters, though, allows us to look at trends of these abundances with age and with Galactocentric distance (Figure 1). There is no evidence for enhanced values of [O/Fe] in the oldest of the clusters (Be 17, Cr 261, and NGC 6791 at 7 -10 Gyr). There is a suggestion that the most distant clusters (Saurer 1 and Be 29) have enhanced [O/Fe], but these values come from the 01 infrared triplet, which has been known to yield values systematically higher than values from the forbidden [01] lines, which are used for the other clusters in the sample. 

The results from [OI] analysis are consistent with those from OH line synthesis, with discrepancies smaller than 0.2 dex in most cases. However, the abundances obtained from the triplet are systematically lower than the [OI] and OH results, with differences of 0.3 dex. The reason of the triplet systematic underabundance could be that the NLTE corrections applied to triplet results correspond... 

Abstract. We present the results from our non-LTE investigation for neutral carbon, which was carried out to remove potential systematic errors in stellar abundance analyses. The calculations were performed for late-type stars and give substantial negative non-LTE abundance corrections. When applied to observations of extremely metal-poor stars, which within the LTE framework seem to suggest a possible [C/O] uprise at low metallicities (Akerman et al. 2004), these improvements will have important implications, enabling us to understand if the standard chemical evolution model is adequate, with no need to invoke signatures by Pop. Ill stars for the carbon nucleosynthesis. 

Fig. 1. Li EW (left panel) and abundances (right panel) of NGC 6530 stars compared to those of the coeval Orion Nebula cluster, using the same growth curves. Most of our targets show very strong Li lines increasing at lower temperatures. The results are not corrected for NLTE and veiling effects, as in Orion in [3]. Absolute values are overestimated but, relative values do not suffer from systematic errors.

Theory doesn t tell us what initial Li a star has, only what depletion it suffers. An accurate estimate of the initial Li abundance is therefore a pre-requisite before observations and models can be compared. The Sun is a unique exception, where we know the present abundance, A(Li) = 1.1 0.1 (where A(Li)= log[AT(Li)/AT(H)] + 12) and the initial abundance of A(Li)= 3.34 is obtained from meteorites. For recently born stars, the initial Li abundance is estimated from photospheric measurements in young T-Tauri stars, or from the hotter F stars of slightly older clusters, where theory suggests that no Li depletion can yet have taken place. Results vary from 3.0 < A(Li) < 3.4, somewhat dependent on assumed atmospheres, NLTE corrections and TeS scales [23,33]. It is of course quite possible that the initial Li, like Fe abundances in the solar neighbourhood, shows some cosmic scatter. Present observations certainly cannot rule this out, leading to about a 0.2 dex systematic uncertainty when comparing observations with Li depletion predictions. 

The first papers in this field suggested that the overall alpha abundances found in the most metal-poor dSph stars are not similar to those found in the halo. However, a more detailed analysis of the individual elements including corrections for differences in log gf values has shown that the O and Mg abundances are consistent with those found in the MW halo, while the Ca and Ti abundances are systematically lower than those in the MW halo, see figure 1, 2 and 6 in Shetrone (2004). This can also be seen in Figure 1 which shows that the most metal-poor Sculptor stars have [Ca/Fe] ratios less than 0.2 dex while the halo median at this metallicity is roughly 0.15 dex larger. 

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