S-process - The S-process Measured in Stardust

The S-process Measured in Stardust

Stardust is one component of cosmic dust. Individual solid grains from various long-dead stars that existed before the solar system are found in meteorites, where they have been preserved. Meteoriticists usually refer to them as Presolar grains. The origin of these grains is demonstrated by laboratory measurements of extremely unusual isotopic abundance ratios within the grain. The results give new insight into astrophysics. Silicon-carbide (SiC) grains condense in the atmospheres of AGB stars and thus trap the isotopes of that star. Because the AGB stars are the main site of the S-process in the galaxy, the heavy elements in the SiC grains are virtually pure S-process isotopes. This fact has been demonstrated repeatedly by sputtering-ion mass spectrometer studies of these presolar grains. Several surprising results have shown that the ratio of S-process and R-process abundances is somewhat different from that which was previously assumed. It has also been shown with trapped isotopes of krypton and xenon that the S-process abundances in the stellar atmospheres change with time or from star to star, presumably with the strength of neutron fluence or perhaps the temperature. This is a frontier of S-process studies today.