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Title:
Testing Rotational Mixing Predictions with New Boron Abundances in Main-Sequence B-Type Stars
Authors:
Mendel, J. T.; Venn, K. A.; Proffitt, C. R.; Brooks, A. M.; Lambert, D. L.
Affiliation:
AA(Macalester College, 1600 Grand Avenue, Saint Paul, MN 55105; ; Current address: Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Mail Number 31, P.O. Box 218, Hawthorn, VIC 3122, Australia; .), AB(Macalester College, 1600 Grand Avenue, Saint Paul, MN 55105; ), AC(Science Programs, Computer Sciences Corporation, 3700 San Martin Drive, Baltimore, MD 21218; ), AD(Astronomy Department, University of Washington, Box 351580, Seattle, WA 98195; ), AE(McDonald Observatory, University of Texas, 1 University Station, Austin, TX 78712-1083 )
Publication:
The Astrophysical Journal, Volume 640, Issue 2, pp. 1039-1050. (ApJ Homepage)
Publication Date:
04/2006
Origin:
UCP
ApJ Keywords:
Stars: Abundances, Stars: Evolution, Stars: Rotation
DOI:
10.1086/500252
Bibliographic Code:
2006ApJ...640.1039M

Abstract

New boron abundances for seven main-sequence B-type stars are determined from HST STIS spectroscopy around the B III 2066 Å line. Boron abundances provide a unique and critical test of stellar evolution models that include rotational mixing, since boron is destroyed in the surface layers of stars through shallow mixing long before other elements are mixed from the stellar interior through deep mixing. The stars in this study are all on or near the main sequence and are members of young Galactic clusters. They show no evidence of mixing with gas from H-burning layers from their CNO abundances. Boron abundances range from 12+log(B/H)<=1.0 to 2.2. The boron abundances are compared to the published values of the stellar nitrogen abundances [all have 12+log(N/H)<=7.8] and to their host cluster ages (4-16 Myr) to investigate the predictions from models of massive star evolution with rotational mixing effects. We find that the variations in boron and nitrogen are generally within the range of the predictions from the stellar evolution models with rotation (where predictions for models with rotation rates from 0 to 450 km s-1 and μ-barriers are examined), especially given their age and mass ranges. Three stars (of 34 B-type stars with detailed boron abundance determinations) deviate from the model predictions, showing either much larger boron depletions than can be explained by the rotating model predictions or a spectroscopic mass that is lower than expected, given the rotating model predictions for its age and abundances. The results from these three stars suggest that rotational mixing could be more efficient than that currently modeled at the highest rotation rates.
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