Boron Abundances in Early Type Stars

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Session 31 -- Massive Hot Stars
Display presentation, Tuesday, 31, 1994, 9:20-6:30

[31.15] Boron Abundances in Early Type Stars

K.A. Venn, D.L. Lambert (U.~Texas at Austin), M.Lemke (Cambridge)

Boron is a trace element in hot stars which can be observed from the B II resonance line at 1362 \AA. We have used IUE archival spectra to examine the B abundances in early type stars. The abundances of boron in A and B-type stars were originally calculated by Boesgaard \& Heacox (1978 ApJ 226, 888) from Copernicus spectra as a method of testing the predictions of galactic cosmic ray spallation reactions.

We are primarily interested in the effects of stellar evolution on B. Boesgaard \& Heacox do not report any relationship between evolutionary state and the B abundance, however there are very few evolved stars in their sample and the few studied have very large uncertainties in B. Boron is destroyed by protons at temperatures above about 4 million K, thus the stellar surface B abundance is a sensitive monitor of evolutionary processes, such as mass loss and mixing, which would lead to large losses in the surface B. Gies \& Lambert (1992 ApJ 387, 673) found evidence of CNO-cycled gas in some slightly evolved B-type stars, suggesting that some mixing may occur in massive stars near the main-sequence. We examine the B abundances in these stars for evidence of a boron-nitrogen relationship.

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