AAS 205th Meeting, 9-13 January 2005
Session 13 Stellar Evolution
Poster, Monday, January 10, 2005, 9:20am-6:30pm, Exhibit Hall

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[13.02] Testing Rotational Mixing in Massive Stars with Boron Abundances in Main-Sequence B-type Stars.

J.T. Mendel, K.A. Venn (Macalester College), C. Proffitt (STScI), A.M. Brooks (University of Washington), D.L. Lambert (University of Texas at Austin)

Boron's role is crucial in verifying the new stellar evolution models of massive stars that include rotation because its surface abundance is depleted at an observable level long before CNO-elements are mixed upwards from the interior to the surface. While most stars with boron depletions do show nitrogen enrichments, Venn et al (2002) found 2 boron-poor stars without nitrogen enhancements; furthermore, they showed that the depletion levels of these 12-13 solar mass stars were uncharacteristically high. In this poster, we present new boron abundances for seven main-sequence B-type stars from HST STIS spectroscopy. These target stars are all members of OB associations, and they have normal, unenriched surface nitrogen abundances, but suggestively weak B III line strengths from archival IUE spectroscopy. Five stars could be studied in fine detail, while the rotational velocities for two stars were so large that we could only estimate their abundances. For all seven targets, the boron abundances, nitrogen abundances, stellar parameters, and ages are all in very good agreement with predictions from the Maeder & Meynet (2000) and Heger & Langer (2000) stellar models, assuming rotational velocities between 200 and 300 km/s.

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© 2004. The American Astronomical Society.