Dust production in the galaxy: The meteorite perspective

Five types of presolar grain have been isolated from meteorites—SiC, ${\mathrm{Si}}_{\mathrm{3}}{\mathrm{N}}_{\mathrm{4}},$ graphite, refractory oxides (${\mathrm{Al}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}$ and ${\mathrm{MgAl}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{4}}$ ), and nanodiamonds. With the exception of the nanodiamonds, single grains from each of the grain types have been isotopically analyzed. From the range of single grain isotopic compositions, a minimum of 35–40 stellar sources (AGB stars, supernovae and, possibly, novae and WR stars) are required. The relative galactic production rates of SiC, ${\mathrm{Si}}_{\mathrm{3}}{\mathrm{N}}_{\mathrm{4}},$ graphite, refractory oxide, and nanodiamond dust recorded by the presolar grains is compared with production rates estimated astronomically. The observed and estimated proportions of SiC from the various stellar sources agree quite well. Relative to the SiC grains, the abundance of supernova graphite grains is also close to astronomical estimates. However, AGB graphite/amorphous carbon, which should dominate, is highly depleted in meteorites. The AGB material may have been destroyed in the ISM or Solar System, but it is possible that the nanodiamonds, which are present in about the right abundance, are the missing carbonaceous material from AGB stars. The refractory presolar oxides are also underabundant compared to the SiC, but, as expected from astronomical data, they are dominated by grains from AGB stars. The oxide underabundance relative to SiC may be due to Al condensing in other phases that have yet to be found and/or because the oxides have a finer grain size distribution than the SiC. Similar reasons may also explain the underabundance of supernova oxide grains compared to AGB ones.