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Title:
Boron Abundances in B-Type Stars: A Test of Rotational Depletion during Main-Sequence Evolution
Authors:
Venn, K. A.; Brooks, A. M.; Lambert, David L.; Lemke, M.; Langer, N.; Lennon, D. J.; Keenan, F. P.
Affiliation:
AA(Macalester College, Saint Paul, MN 55105; Department of Astronomy, University of Minnesota, 116 Church Street, Minneapolis, MN 55455.), AB(Macalester College, Saint Paul, MN 55105), AC(University of Texas at Austin, Austin, TX 78712), AD(Dr. Karl Remeis-Sternwarte Bamberg, Sternwartstrasse 7, Bamberg D-96049, Germany), AE(Department of Physics and Astronomy, University of Utrecht, P.O. Box 80000, Utrecht, TA 3508, Netherlands), AF(Isaac Newton Group of Telescopes, Apatado de Correos 321, Santa Cruz de La Palma, Canary Islands E-38780, Spain), AG(Department of Pure and Applied Physics, the Queen's University of Belfast, Belfast BT7 1NN, Northern Ireland)
Publication:
The Astrophysical Journal, Volume 565, Issue 1, pp. 571-586. (ApJ Homepage)
Publication Date:
01/2002
Origin:
UCP
ApJ Keywords:
Stars: Abundances, Stars: Evolution, Stars: Rotation
DOI:
10.1086/324435
Bibliographic Code:
2002ApJ...565..571V

Abstract

Boron abundances have been derived for seven main-sequence B-type stars from Hubble Space Telescope STIS spectra around the B III λ2066 line. In two stars, boron appears to be undepleted with respect to the presumed initial abundance. In one star, boron is detectable but is clearly depleted. In the other four stars, boron is undetectable, implying depletions of 1-2 dex. Three of these four stars are nitrogen enriched, but the fourth shows no enrichment of nitrogen. Only rotationally induced mixing predicts that boron depletions are unaccompanied by nitrogen enrichments. The inferred rate of boron depletion from our observations is in good agreement with these predictions. Other boron-depleted nitrogen-normal stars are identified from the literature. In addition, several boron-depleted nitrogen-rich stars are identified, and while all fall on the boron-nitrogen trend predicted by rotationally induced mixing, a majority have nitrogen enrichments that are not uniquely explained by rotation. The spectra have also been used to determine iron group (Cr, Mn, Fe, and Ni) abundances. The seven B-type stars have near-solar iron group abundances, as expected for young stars in the solar neighborhood. We have also analyzed the halo B-type star PG 0832+676. We find [Fe/H]=-0.88+/-0.10, and the absence of the B III line gives the upper limit [B/H]<-2.5. These and other published abundances are used to infer the star's evolutionary status as a post-asymptotic giant branch star. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with proposal GO 07400.
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