Known types of presolar grains

Carrier of PI (=Q) noble gases Probably organic compounds n.d. n.d. 

Resonance ionization mass spectrometry (RIMS) is much more efficient at getting ions into the detectors. First, atoms are removed from the sample surface with a pulsed laser, which can release the atoms thermally without ionizing them. Then, by using carefully tuned lasers, the element of interest in the resulting gas plume can be ionized at almost 100% efficiency, while other elements are not ionized at all. The ions are extracted into a time-of-flight 

Bulk techniques still have a place in the search for presolar components. Although they cannot identify the presolar grain directly, they can measure anomalous isotopic compositions, which can then be used as a tracer for separation procedures to identify the carrier. There are several isotopically anomalous components whose carriers have not been identified. For example, an anomalous chromium component enriched in 54Cr appears in acid residues of the most primitive chondrites. The carrier is soluble in hydrochloric acid and goes with the colloidal fraction of the residue, which means it is likely to be submicron in size (Podosck el al., 1997). Measurements of molybdenum and ruthenium in bulk primitive meteorites and leachates from primitive chondrites show isotopic anomalies that can be attributed to the -process on the one hand and to the r- and /7-processes on the other. The s-process anomalies in molybdenum and ruthenium correlate with one another, while the r- and /7-process anomalies do not. The amounts of -process molybdenum and ruthenium are consistent with their being carried in presolar silicon carbide, but they are released from bulk samples with treatments that should not dissolve that mineral. Thus, additional carriers of s-, r-, and/ -process elements are suggested (Dauphas et al., 2002). 

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Only modest isotopic variations of 35C1 are expected in various astrophysical samples because both stable isotopes are made in the same burning zones but these have not been measurable to date. Known types of presolar grains contain little Cl. 

The carriers of anomalous Ne-E (two forms of which were now known) and Xe-S were quickly identified. Neon-E(H), which is released at temperatures above 1200 °C in stepped heating experiments, and Xe-S were found to be carried in presolar silicon carbide (Tang and Anders, 1988). Neon-E(L), which is released below 900 °C, was found to be carried by presolar graphite (Amari et al., 1990). Once these presolar compounds were shown to be present in meteorites, studies were carried out to identify all of the different types of meteorites that carry presolar grains. Concentrated searches for other presolar phases were also initiated, and many new types of presolar grains have been found. This work is just beginning, however, and we cannot yet account for the majority of the presolar components that must have been present in the Sun s parent molecular cloud. 

The alternative hypothesis, that of a nucleosynthetic component carried into the early solar system by 0-rich presolar dust (see discussion in Clayton 1993) remains plausible after all, as mentioned in the Introduction, trace amounts of presolar dust is known to exist in the matrices of chondrites. However, all the high spatial (ion microprobe) measurements of the many types of primitive refractory materials discussed here have failed to find any very extreme oxygen isotopic anomalies such as might be expected if pure 0 dust (e.g. from a supernova) were incorporated into CAIs or AOAs along with local condensates. Even among the -100 true interstellar oxide grains that... 

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