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首页> 外文期刊>The Astrophysical journal >DISCOVERY OF ABUNDANT IN SITU SILICATE AND SPINEL GRAINS FROM RED GIANT STARS IN A PRIMTIVE METEORITE
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DISCOVERY OF ABUNDANT IN SITU SILICATE AND SPINEL GRAINS FROM RED GIANT STARS IN A PRIMTIVE METEORITE

机译：从主陨石中的红色巨星中发现大量的原生硅酸盐和尖晶石

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摘要

We report the discovery of 12 in situ presolar silicate and spinel grains, 140-590 nm in size, in the Acfer 094 meteorite. These grains represent a matrix-normalized abundance of presolar O-rich dust of 170 parts per million. Among the 10 silicate grains are three olivines, four pyroxenes, and three grains with glasslike composition. Eleven grains have large excesses in ~(17)O with ~(17)O/~(16)O ratios of up to 2.9 times the solar ratio and slightly lower than or close-to-solar ~(18)O/~(16)O ratios. These grains most likely formed in 1.5-1.65 solar mass red giant branch (RGB) or asymptotic giant branch (AGB) stars with close-to-solar metallicity. One pyroxene grain has close-to-solar ~(17)O/~(16)O and ~(18)O/~(16)O of 3.8 times solar. Silicon- and Fe-isotopic ratios of this grain are suggestive of the formation in an RGB or AGB star, probably with higher-than-solar metallicity. ~(29)Si/~(28)Si and ~(30)Si/~(28)Si ratios of the silicate grains vary by ～16%, are positively correlated with one another, and fall to the ~(30)Si-poor side of the Si mainstream line characteristic for presolar SiC from AGB stars. This gives independent confirmation for the view that the Si mainstream line reflects the Galactic chemical evolution of the Si isotopes, except for a small shift due to dredge-up of matter from the He shell in AGB stars.
机译：我们报告在Acfer 094陨石中发现了12个原位的日光硅酸盐和尖晶石晶粒，尺寸为140-590 nm。这些颗粒代表了百万分之170的富含O的太阳前基质的矩阵归一化含量。在这10个硅酸盐晶粒中，有3个橄榄石，4个辉石和3个具有玻璃状成分的晶粒。 〜（17）O中有11个晶粒有大量过量，~~（17）O /〜（16）O的比例高达日光比的2.9倍，略低于或接近于〜（18）O /〜（ 16）O比率。这些晶粒最有可能在1.5-1.65太阳质量的红色巨型分支（RGB）或渐近巨型分支（AGB）恒星中形成，具有接近太阳能的金属性。一个辉石晶粒具有接近太阳的3.8倍的〜（17）O /〜（16）O和〜（18）O /〜（16）O。该晶粒的硅和铁同位素比表明在RGB或AGB恒星中形成，可能具有高于太阳能的金属性。硅酸盐晶粒的〜（29）Si /〜（28）Si和〜（30）Si /〜（28）Si比值变化约〜16％，彼此成正相关，并下降到〜（30）Si AGB恒星前期SiC的Si主流线特性的较差一侧。这独立地证实了以下观点，即硅主流线反映了硅同位素的银河化学演化，只是由于AGB恒星中He壳中的物质被疏通而产生了微小变化。

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