Volume 481, Number 2, April II 2008
|Page(s)||453 - 463|
|Section||Stellar structure and evolution|
|Published online||04 February 2008|
Nitrogen enrichment, boron depletion and magnetic fields in slowly-rotating B-type dwarfs
Katholieke Universiteit Leuven, Departement Natuurkunde en Sterrenkunde, Instituut voor Sterrenkunde, Celestijnenlaan 200D, 3001 Leuven, Belgium e-mail: firstname.lastname@example.org
2 European Southern Observatory, Casilla 19001, Santiago, Chile
Accepted: 15 January 2008
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.
Key words: stars: early-type / stars: fundamental parameters / stars: abundances / stars: atmospheres / stars: magnetic fields
© ESO, 2008
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