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Accession Number N20120011866
Title Observational Effects of Magnetism in O Stars: Surface Nitrogen Abundances.
Publication Date Dec 2011
Media Count 14p
Personal Author C. Escolano F. Martins G. A. Wade J. C. Bouret J. F. Donati
Abstract Aims. We investigate the surface nitrogen content of the six magnetic O stars known to date as well as of the early B-type star Tau Sco.. We compare these abundances to predictions of evolutionary models to isolate the effects of magnetic field on the transport of elements in stellar interiors. Methods. We conduct a quantitative spectroscopic analysis of the ample stars with state-of-the-art atmosphere models. We rely on high signal-to-noise ratio, high resolution optical spectra obtained with ESPADONS at CFHT and NARVAL at TBL. Atmosphere models and synthetic spectra are computed with the code CMFGEN. Values of N/H together with their uncertainties are determined and compared to predictions of evolutionary models. Results. We find that the magnetic stars can be divided into two groups: one with stars displaying no N enrichment (one object); and one with stars most likely showing extra N enrichment (5 objects). For one star (Ori C) no robust conclusion can be drawn due to its young age. The star with no N enrichment is the one with the weakest magnetic field, possibly of dynamo origin. It might be a star having experienced strong magnetic braking under the condition of solid body rotation, but its rotational velocity is still relatively large. The five stars with high N content were probably slow rotators on the zero age main sequence, but they have surface N/H typical of normal O stars, indicating that the presence of a (probably fossil) magnetic field leads to extra enrichment. These stars may have a strong differential rotation inducing shear mixing. Our results shOuld be viewed as a basis on which new theoretical simulations can rely to better understand the effect of magnetism on the evolution of massive stars.
Keywords B stars
Early stars
Magnetic effects
Magnetic fields
Magnetic stars
Massive stars
O stars
Quantitative analysis
Signal to noise ratios
Spectroscopic analysis
Stellar evolution
Stellar models
X ray sources

Source Agency National Aeronautics and Space Administration
NTIS Subject Category 54B - Astronomy & Celestial Mechanics
Corporate Author Goddard Space Flight Center, Greenbelt, MD.
Document Type Journal article
Title Note N/A
NTIS Issue Number 1301
Contract Number N/A

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