Nitrogen enrichment, boron depletion and magnetic fields in slowly-rotating B-type dwarfs

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作者
Morel, T. [1 ,3 ]
Hubrig, S. [2 ]
Briquet, M. [1 ]
机构
[1] Katholieke Universiteit Leuven, Departement Natuurkunde en Sterrenkunde, Instituut voor Sterrenkunde, Celestijnenlaan 200D, 3001 Leuven, Belgium
[2] European Southern Observatory, Casilla 19001, Santiago, Chile
[3] Institut d'Astrophysique et de Géophysique, Université de Liège, BǍt. B5c, Allée du 6 Aoǔt, 4000 Liège, Belgium
来源
Astronomy and Astrophysics | 2008年 / 481卷 / 02期
关键词
Evolutionary models for massive stars; accounting for rotational mixing effects; do not predict any core-processed material at the surface of B dwarfs with low rotational velocities. Contrary to theoretical expectations; we present a detailed and fully-homogeneous; NLTE abundance analysis of 20 early B-type dwarfs and (sub)giants that reveals the existence of a population of nitrogen-rich and boron-depleted; yet intrinsically slowly-rotating objects. The low-rotation rate of several of these stars is firmly established; either from the occurrence of phase-locked UV wind line-profile variations; which can be ascribed to rotational modulation; or from theoretical modelling in the pulsating variables. The observational data presently available suggest a higher incidence of chemical peculiarities in stars with a (weak) detected magnetic field. This opens the possibility that magnetic phenomena are important in altering the photospheric abundances of early B dwarfs; even for surface field strengths at the one hundred Gauss level. However; further spectropolarimetric observations are needed to assess the validity of this hypothesis. © 2008 ESO;
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页码:453 / 463
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