Trends in the study of presolar dust grains from primitive meteorites

Abstract

Abstract-A series of trends can be discerned in the study of presolar dust grains from primitive meteorites, and these trends might give us hints in which direction this new field of astronomy is developing. They include: (1) a focus on ever smaller components of meteorites; (2) a shift from the study of the elemental abundances in the solar system to the study of isotopic abundances; (3) a shift of emphasis from averages of the isotopic abundances as represented by the whole solar system to individual isotopic components preserved in circumstellar dust grains; (4) the preferential study of rare types of presolar dust grains; ( 5 ) the emergence of new technical capabilities for the study of individual presolar dust grains; examples include isotopic imaging and resonance ionization mass spectrometry (RIMS); and (6) a shift from a situation in which grain data confirm previously held theoretical ideas to a situation in which the experimental data impose new constraints on theoretical models of nucleosynthesis, stellar mixing and grain formation in stellar outflows. In other words, the data do not confirm but drive the theory. An example is the distribution of Si isotopic ratios in individual mainstream S i c grains for which many different theoretical explanations have been offered.There are still many unsolved problems posed by the grain data, the most difficult being the interpretation of the isotopic ratios of grains with a supernova signature (evidence for 44Ti and excesses in 28Si) in terms of theoretical models of nucleosynthesis and the mixing of supernova ejecta. Future progress is expected to come from the analysis of larger numbers of grains, the search for new types of presolar grains, the analysis of smaller grains and of more elements in a given grain, both made possible by the increase in sensitivity of ion microprobes and the extended application of RIMS, from multi-dimensional models of stellar evolution with enlarged nuclear networks, and from new measurements of nuclear cross sections.

ON THE FORMATION OF SILACYCLOPROPENYLIDENE (c-SiC2H2) AND ITS ROLE IN THE ORGANOSILICON CHEMISTRY IN THE INTERSTELLAR MEDIUM

“…Due to the simultaneous abundance of silicon dicarbide (Thaddeus et al 1984), organosilicon clusters are considered as key building blocks in the synthesis of more complex silicon-bearing molecules such as SiC 3 and SiC 4 , which eventually lead to silicon-carbide dust grains (Ohishi et al 1989). Sophisticated isotope analysis verified that the silicon-carbide stardust recovered from meteorites originates essentially from AGB stars with smaller portions formed in Type II supernovae and novae (Zinner 1998).…”

s-Processing in AGB Stars Revisited. III. Neutron captures from MHD mixing at different metallicities and observational constraints

“…In this context, it will be necessary to compute not only the average abundances gradually formed in the envelopes, but also those of the He-shell material cumulatively transported by TDU episodes. This represents an s-process-enhanced, C-rich phase averaged over the efficiency of mixing, which is called, since many years (Zinner 1998), the G component. In our models, the G-component carries abundances very similar to those of flux tubes that, due to strong magnetic tension, were to survive destruction by turbulence in the convective envelope, opening later in the wind, as occurring in the Sun (Pinto et al 2016).…”

CEMP stars: possible hosts to carbon planets in the early Universe

“…Under such circumstances, the gas clouds which collapse and fragment to form these CEMP-no stars and their protostellar disks may contain significant amounts of carbon dust grains. Observationally, dust formation in SNe ejecta has been inferred from isotopic anomalies in meteorites where graphite, SiC, and Si3N4 dust grains have been identified as SNe condensates (Zinner 1998). Furthermore, in situ dust formation has been unambiguously detected in the expanding ejecta of SNe such as SN 1987A (Lucy et al 1989;Indebetouw et al 2014) and SN 1999em (Elmhamdi et al 2003.…”