Astromat

The NanoSIMS 50L at NASA JSC was used to remeasure presolar grains identified in polished grain OREX-803172-0 for C and Si isotopes (for C-rich presolar grains) or O and Si isotopes (for O-rich presolar grains). This was performed by raster ion imaging at < 8 micrometer fields of view. The data were collected with the goal of determining isotopic compositions with greater precision and to constrain the grain phase (i.e., SiC or graphite, silicate or oxide). San Carlos Olivine was measured as an O isotopic standard, and graphite was measured as a C isotopic standard. Si isotopes were normalized to the matrix surrounding a presolar grain.