Barium isotopes in individual presolar silicon carbide grains from the Murchison meteorite

Abstract

Abstract-Barium isotopic compositions of single 2.3-5.3 m presolar SiC grains from the Murchison meteorite were measured by resonant ionization mass spectrometry. Mainstream SiC grains are enriched in s-process barium and show a spread in isotopic composition from solar to dominantly s-process. In the relatively coarse grain size fraction analyzed, there are large grain-to-grain variations of barium isotopic composition. Comparison of single grain data with models of nucleosynthesis in asymptotic giant branch (AGB) stars indicates that the grains most likely come from low mass carbon-rich AGB stars (1.5 to 3 solar masses) of about solar metallicity and with approximately solar initial proportions of r-and s-process isotopes. Measurements of single grains imply a wide variety of neutron-to-seed ratios, in agreement with previous measurements of strontium, zirconium and molybdenum isotopic compositions of single presolar SiC grains.

Reservoir for Comet Material: Circumstellar Grains

“…Other signatures of H and He burning in SiC mainstream grains are the former presence of radioactive 26 Al (Hoppe et al 1994;Huss et al 1997) and large isotopic overabundances of 22 Ne (e.g., ). The isotopic patterns of the intermediate-mass to heavy elements show the imprints of s-process (slow neutron capture) nucleosynthesis (e.g., Nicolussi et al 1997Nicolussi et al , 1998Savina et al 2003;), in agreement with theoretical predictions for 1-3 M AGB stars . It is interesting to note in this context that the detection of the radioactive s-process isotope 99 Tc (half life 200,000 years) in the spectra of AGB stars (Merrill 1952) has been the first direct evidence that the chemical elements are produced in the interior of stars.…”

Tungsten Nuclear Anomalies in Planetesimal Cores

“…For heavy elements, these variations may reflect incomplete mixing of products of stellar nucleosynthesis (s-, r-, and p-processes) in the solar nebula. Similar anomalies, albeit of much larger magnitudes, were also measured in single presolar grains that formed in stellar outflows before formation of the Sun (Zinner et al 1991;Nicolussi et al 1997Nicolussi et al , 1998aNicolussi et al , 1998bNicolussi et al , 1998cSavina et al 2003Savina et al , 2004Barzyk et al 2006;Terada et al 2006). The presence of these anomalies calls into question the assumption that the early solar system was thoroughly homogenized, which can undermine the use of several short-lived radiochronometers, including 182 Hf.…”

Nucleosynthetic Signatures in Presolar SiC and Graphite Grains

“…Analyses of mainstream grains indicate that their parent stars are close-to-solar metallicity [42] and gave constraints for the range of 13 C pocket efficiencies [43].…”