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Scientific paper
Dec 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997hst..prop.7750s&link_type=abstract
HST Proposal ID #7750
Other
Hst Proposal Id #7750 Interstellar Matter
Scientific paper
We propose a study to obtain high quality interstellar abundance data {i.e. S/N 500-1000} for the heavy atom Cd {Z = 48}, an element produced mainly by s-process neutron capture in intermediate-to-low mass AGB stars, to explore nucleosynthetic enrichment in the ISM. The only existing ISM measure of Cd, in a sight line characterized by large gas depletions onto dust, yields an abundance consistent with the solar value. However, since Cd should be chemically similar to Zn, an element with a common outer electron shell structure but which is depleted from solar by at least a factor 3 in this sight line, we suspect that Cd must be somewhat depleted onto dust. We believe the apparent solar abundance of Cd reflects the fact that the true ISM reference { cosmic} abundance is larger than the solar value, reflecting an increase since the formation of the solar system 4.5 billion years ago. This supposition is not unreasonable - observations of other heavy s-process elements in the atmospheres of some AGB stars show substantial enrichments and so we expect that some heavy s-process element enrichment of the ISM must have occurred. The science proposed here provides an opportunity to determine the degree of post- stellar evolution enrichment, yielding important information on bulk s-process yields and cumulative injection of this material into the ISM over the past 4.5 billion years. Because this program requires S/N values unobtainable with STIS, this represents the last opportunity to do this type of science.
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