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The oxygen isotopic compositions of densely packed submicron oxide grains in two grain separates of different grain size from the CM2 carbonaceous chondrite Murray were determined by multi-detection raster imaging on the NanoSIMS ion microprobe. This led to the identification of 81 presolar spinel and 3 presolar corundum grains among ∼51 700 grains in the CF residue (mean diameter 0.15 µm) and 171 presolar spinel and 29 presolar corundum grains among ˜21 500 grains in the CG residue (mean diameter 0.45 µm). Previous NanoSIMS analysis of individual grains from the same residues has led to the discovery of 15 presolar spinel and 3 presolar corundum grains among 628 CF grains, and 9 presolar spinels among 753 CG grains. The oxygen isotopic compositions of the presolar oxides found by raster imaging are comparable to those of the presolar oxides measured individually. While the abundance of presolar spinel among the (larger) grains of the CG residue is the same for both techniques, the detection efficiency for presolar spinel by imaging among the (smaller) grains in CF is lower due to the small size of these grains. Nonetheless, it is possible to identify presolar grains of this size range. Though single grain measurements are effective for determining the precise isotopic compositions and abundances of presolar grains, raster ion imaging is the method of choice in searches for rare presolar grain types such as presolar silicates.
Among presolar SiC grains found in the Murchison carbonaceous meteorites (average size less than 0.5 μm) are very large grains, ranging in size up to 50 μm. We interpret 6Li excesses measured in eight of these grains as being the result of spallation reactions by Galactic cosmic rays during the time the grains spent in the interstellar medium before their incorporation into the meteorite. Derived interstellar exposure ages range from 40 My to 1 Gy, the highest values being consistent with theoretical expectations of interstellar grain lifetimes. Although six grains have almost identical C and Si isotopic compositions, their exposure ages are very different. This observation, combined with low trace element contents, and unusual grain sizes, raises fundamental questions about their stellar sources.
Infrared observations of nova light curves reveal that classical novae form grains in the expanding shells, ejected into the interstellar medium as a consequence of a violent outburst. Such grains contain nucleo-synthetic fingerprints of the nova explosion. In this paper, we analyse different isotopic signatures expected to be present in nova grains on the basis of detailed hydrodynamic calculations of CO and ONe novae and compare them with recent determinations of presolar nova grains from the Acfer 094 and Murchison meteorites.
Knowledge about the age of presolar grains provides important insights into Galactic chemical evolution and the dynamics of grain formation and destruction processes in the Galaxy. Determination from the abundance of cosmic ray interaction products is straightforward, but in the past has suffered from uncertainties in correcting for recoil losses of spallation products. The problem is less serious in a class of large (tens of μm) grains. We describe the correction procedure and summarise results for He and Ne ages of presolar SiC ‘Jumbo’ grains that range from close to zero to ∼850 Myr, with the majority being less than 200 Myr. We also discuss the possibility of extending our approach to the majority of smaller SiC grains and explore possible contributions from trapping of cosmic rays.
Primitive meteorites and interplanetary dust particles contain small grains that originated in stellar outflows and supernova explosions. These μm- and sub-μm-sized presolar grains can be isolated and studied for their isotopic compositions in the laboratory. They are recognised as stardust by their isotopic compositions, which are completely different from those of the Solar System. They provide new information on stellar evolution, nucleosynthesis, mixing processes in asymptotic giant branch (AGB) stars and supernovae, and Galactic chemical evolution. Red giants, AGB stars, Type II supernovae and possibly novae have been identified as stellar sources of the grains. Of the eight nuclear processes proposed by Burbidge et al. (1957), signatures of all except the r-process can be found in presolar dust grains.
The WGARG was created in 2001 to oversee the rapid growth of the quantitative determination and understanding of the abundance patterns seen in red-giant stars. As the field progresses we are regularly reminded of how broad and multi-disciplinary is this area of research.
The main activity of the WG on Abundances in Red Giants has been to propose a JD for the IAU GA in 2009. The increasing evidence for distinct populations within globular clusters is leading to the view that there is a continuum between globular clusters and the smallest of the galaxies. Our JD was designed to investigate this link. However, our JD was incorporated into IAU Symposium No. 266 Star Clusters: Basic Building Blocks throughout Time and Space for the IAU XXVII in Rio de Janeiro, 2009. We will be responsible for organising one session in the Symposium to cover the agenda put forward in our JD proposal.
Ultimately, all of the solids in the Solar System, including ourselves, consist of elements that were made in stars by stellar nucelosynthesis. However, most of the material from many different stellar sources that went into the making of the Solar System was thoroughly mixed, obliterating any information about its origin. An exception are tiny grains of preserved stardust found in primitive meteorites, micrometeorites, and interplanetary dust particles. These μm- and sub-μm-sized presolar grains are recognized as stardust by their isotopic compositions, which are completely different from those of the Solar System. They condensed in outflows from late-type stars and in SN ejecta and were included in meteorites, from which they can be isolated and studied for their isotopic compositions in the laboratory. Thus these grains constitute a link between us and our stellar ancestors. They provide new information on stellar evolution, nucleosynthesis, mixing processes in asymptotic giant branch (AGB) stars and supernovae, and galactic chemical evolution. Red giants, AGB stars, Type II supernovae, and possibly novae have been identified as stellar sources of the grains. Stardust phases identified so far include silicates, oxides such as corundum, spinel, and hibonite, graphite, silicon carbide, silicon nitride, titanium carbide, and Fe-Ni metal.
Unfortunately the Business Meeting clashed with interesting sessions on stellar convection theory that were very relevant to most members of this Working Group. Hence the attendance was very small, and some preliminary discussions were later followed up by email among the Organising Committee members.
Determining and understanding the abundances seen in red-giant stars has taken a central role in our understanding of many branches of modern astrophysics. Activity in the area continues apace, both in terms of the fundamental physics of the stellar nucleosynthesis as well as its implications for wider fields. A major role of the Working Group has been to facilitate meetings where the fundamental role of these stars can be further understood and exploited by other researchers.
The carbon and nitrogen isotopic ratios of pre-solar SiC grains of type A+B suggest a proton-limited nucleosynthetic process as encountered, for instance, during the very late thermal pulse of post-AGB stars. We study the nuclear processes during this phase and find carbon and nitrogen isotopic ratios which can reproduce those of A+B grains. These results are still preliminary because they depend on uncertain factors such as the details of mixing during the post-AGB thermal pulse, the rates of some nuclear reactions, and the assumptions on mixing during the progenitor AGB phase.
Primitive meteorites contain dust grains that predate the Solar System, formed in stellar atmospheres and thus represent samples of ancient Stardust. Among the presolar grain types identified so far, corundum (Al2O3) and silicon carbide (SiC) are inferred to originate from AGB stars. Corundum grains carry the signatures of core H burning in their O isotopes and of shell H burning during the AGB phase in the form of extinct 26Al. In presolar SiC, most of which originated from carbon stars, the C and N isotopes and 26Al reflect core and shell H burning and shell He burning. In addition, many elements that carry the isotopic signature of neutron capture have also been measured. Most individual grains show excesses in 29Si and 30Si, but the contribution from neutron capture is only a minor effect and the major effect is due to galactic heterogeneity. Noble gases and the elements Ba, Nd, Sm, and Dy are measured in ”bulk samples”, collections of many grains. Their measured isotopic patterns are well reproduced by models of the s-process in AGB stars. Recently, the isotopic analysis of Sr, Zr and Mo in single SiC grains has been made possible by resonance ionization mass spectrometry. These measurements also point to low-mass AGB stars as the most likely sources. Specifically, large 96Zr depletions in some grains indicate that the 22Ne(α, n) source was not active in the grains' parent stars.
Well-preserved interstellar grains occur in carbonaceous chondrites. Diamond (10-100å) contains r- and p-process Xe (suggesting a supernovae connection), and appears to have formed by stellar condensation, not by interstellar shocks. SiC (mainly 0.1-1 μm) is labeled either with s-process Xe, Kr (red giant?) or with Ne22, N15 (nova?), and shows large isotopic variations in N (100x), C (16x), and Si (1.3x). As Si is unaffected by H, He-burning, the Si variations reflect the isotopic heterogeneity of the ISM on the scale of individual stars; the Si compositions found thus far require at least 6 separate stars.
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