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[35.12] Measurement of the B Isotope Ratio in old stars

D.K. Duncan, L.M. Rebull (Univ. of Chicago)

HST observations have led to new theories of how cosmic rays (CRs) rich in CNO in regions of massive star formation may contribute to the formation of the light elements Li, Be, and B. The neutrino process in SN, which has never been experimentally verified, should also produce boron, but only ¹¹B, yielding a very different isotopic ratio than CR spallation. The boron isotope ratio, ¹¹B/¹⁰B, can provide a definitive test of both these theories, but its galactic evolution is completely unknown.

Our previous GHRS echelle observation of the moderately metal-poor([Fe/H]=-1.0) star HD76932 placed a limit on its B isotope ratio, but not a definite value, because possible blending from an unknown spectrum line could not be ruled out (Rebull etal, ApJ 507, 387, 1998). The discovery of a halo star greatly depleted in B (Primas etal ApJ 506, L51, 1998) provides a wonderful opportunity to make the result definite. By comparing two similar ([Fe/H] \approx -1.6) stars, which have very different amounts of B, we can rule out or measure any blends. This should give a definite result for ¹¹B/¹⁰B at metallcity [Fe/H] \approx -1.6, an epoch when massive star SN should have dominated galactic nucleosynthesis. STIS observations of the low-B star are in hand, and the comparison star is scheduled to be observed in May. We hope to report a defininte result at the June AAS meeting.

This research is supported by NASA grant GO-08197.01.

The author(s) of this abstract have provided an email address for comments about the abstract: duncan@oddojb.uchicago.edu

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