Detection of ^11B/^10B and Galactic Chemical Evolution

Details Detection of ^11B/^10B and Galactic Chemical Evolution Detection of ^11B/^10B and Galactic Chemical Evolution

Jul 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995hst..prop.5860d&link_type=abstract

HST Proposal ID #5860

Computer Science

Hst Proposal Id #5860 Cool Stars

Scientific paper

We propose to use the GHRS in echelle mode to resolve the isotopic splitting of the ^11B and ^10B features at 2090Angstrom. These lines have been observed in the laboratory by one of us (Johansson) to be split by 25mAngstrom, the echelle resolution of GHRS, and we demonstrate that detection is possible. HST B obs. are now used as key data in models of galactic chemical evolution, under the assumption that the B comes from cosmic ray (CR) spallation. This is likely, but not certain (e.g. Duncan, Lambert, Lemke 1992). Woosley et al. (1990) suggest that B may be directly produced in supernovae. No simple models of galactic evolution reproduce both light element (Li, Be, and B) evolution and Fe and O evolution well at the same time. Since the predictions of spallation are quite exact as to isotopic composition, a few or even one observation of the B isotope ratio outside the solar system (the only place ^11B/^10B has been observed) would be an enormous help to constrain theory. A similar detection has been achieved by one of us (Thorburn) for the isotope ^6Li in a halo star. Our program is carefully optimized as to target stars. Since the solar system ^11B/^10B ratio does not match theory, we suggest (first) observing bright solar- metallicicty and intermed metal-poor stars. There high S/N can be achieved and B isotope ratio is predicted to have a large change. More metal-poor stars should follow.

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