Other
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29s.437a&link_type=abstract
Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 437-438
Other
1
Chemical Analysis, Graphite, Interstellar Space, Isotopic Labeling, Meteoritic Composition, Murchison Meteorite, Abundance, Carbon Isotopes, Chemical Composition, Interstellar Chemistry, Nitrogen Isotopes, Trace Elements
Scientific paper
We continue with multielement isotopic analyses of single graphite grains from various density fractions extracted from Murchison. Previous measurements have shown that different density fractions have different isotopic ratios and trace-element contents, suggesting multiple stellar sources for interstellar graphite. One goal is to identify these stellar sources. In this work we report isotopic ratios of graphite grains from the high-density fraction KFC1 (2.15-2.20 g/cu cm, greater than 1 micron) and compare them with results on the low-density fraction KE3 (1.68-1.71 g/cu cm, greater than 3 microns). To be able to obtain multielement isotopic data, we chose larger grains. Forty-five grains were analyzed for their C and N isotopic ratios and the C and N isotopic compositions of KFC1 and KE3 are plotted. As previously observed, most grains in this fraction have isotopically light C. Only three grains have heavy N with N-14/N-15 ratios less than 250 (2 sigma) (solar ratio; 272). The others have normal N. Of 40 grains measured for their O-18/O-16 ratios, all have normal ratios within errors. This is in contrast to graphite grains from KE3, of which two-thirds have O-18 excesses that range up to 100 times solar. Since large O-18 excesses can be generated in massive stars such as Wolf Rayet stars or supernovae, the O-18 excesses in KE3 suggest that a large fraction of low-density graphite grains originate from massive stars, while the contribution from massive stars is small to negligible in the high-density fraction KFC1. This agrees with the conclusions derived from Kr isotopic ratios for these fractions. A striking difference between the density fractions can also be seen for Al-26/Al-27 ratios. The Kr isotopic ratios measured in KFC1 suggest that AGB stars of low metallicity contributed high-density graphite grains.
Amari Sachiko
Lewis Reed S.
Zinner Emst
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