墨累陨石尖晶石星尘的自动NanoSIMS测量
Automated NanoSIMS Measurements of Spinel Stardust from the Murray Meteorite
摘要：
我们报告新的O同位素数据41 presolar氧化物颗粒，38 MgAl 2 O 4（尖晶石）和3 Al 2 O3从CM 2陨石默里，确定与最近开发的自动测量系统的NanoSIMS。我们还获得了29个相同的颗粒（26尖晶石和3 Al_2O_3）的Mg-Al同位素结果。大部分的颗粒具有O同位素组成的典型的大多数前太阳氧化物，落入之前定义的四个组，最有可能是从红巨星分支或渐近巨星分支恒星的凝聚物。我们还发现了几种具有更不寻常的O和Mg成分的颗粒，这表明它们是在极端的天体物理环境中形成的，例如新星和超新星。其中一颗颗粒富含17 O、25 Mg和26 Mg，这些同位素特征表明新星喷出物的凝结。另外还发现了两颗超新星起源的颗粒：一颗具有典型的第4族前氧化物的大18 O/16 O比;另一颗颗粒富含16 O，并且还含有来自44 Ti衰变的放射性44 Ca，这可能是来自II型超新星富O内部区域的物质的冷凝物。此外，一些第2族的前太阳尖晶石颗粒也有很大的25镁和26镁同位素异常，这是很难解释的标准核合成在低质量的恒星。俄歇元素光谱分析进行的颗粒和定性表明，前太阳尖晶石可能不具有高于化学计量比的Al/Mg比，在这里获得的SIMS结果和以前的报道相反。
英文摘要：
We report new O isotopic data on 41 presolar oxide grains, 38 MgAl2O4 (spinel) and 3 Al2O3 from the CM2 meteorite Murray, identified with a recently developed automated measurement system for the NanoSIMS. We have also obtained Mg-Al isotopic results on 29 of the same grains (26 spinel and 3 Al2O3). The majority of the grains have O isotopic compositions typical of most presolar oxides, fall well into the four previously defined groups, and are most likely condensates from either red giant branch or asymptotic giant branch stars. We have also discovered several grains with more unusual O and Mg compositions suggesting formation in extreme astrophysical environments, such as novae and supernovae. One of these grains has massive enrichments in 17O, 25Mg, and 26Mg, which are isotopic signatures indicative of condensation from nova ejecta. Two grains of supernova origin were also discovered: one has a large 18O/16O ratio typical of Group 4 presolar oxides; another grain is substantially enriched in 16O, and also contains radiogenic 44Ca from the decay of 44Ti, a likely condensate from material originating in the O-rich inner zones of a Type II supernova. In addition, several Group 2 presolar spinel grains also have large 25Mg and 26Mg isotopic anomalies that are difficult to explain by standard nucleosynthesis in low-mass stars. Auger elemental spectral analyses were performed on the grains and qualitatively suggest that presolar spinel may not have higher-than- stoichiometric Al/Mg ratios, in contrast to SIMS results obtained here and reported previously.
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