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arXiv · 1008.3086

No detection of large-scale magnetic fields at the surfaces of Am and HgMn stars

M. Auriere·G. A. Wade·F. Lignieres·A. Hui-Bon-Hoa·J. D. Landstreet·I. Iliev·J. -F. Donati·P. Petit·T. Roudier·S. Theado
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Abstract

We investigate the magnetic dichotomy between Ap/Bp and other A-type stars by carrying out a deep spectropolarimetric study of Am and HgMn stars. Using the NARVAL spectropolarimeter at the Telescope Bernard Lyot (Observatoire du Pic du Midi, France), we obtained high-resolution circular polarisation spectroscopy of 12 Am stars and 3 HgMn stars. Using Least Squares Deconvolution (LSD), no magnetic field is detected in any of the 15 observed stars. Uncertaintiies as low as 0.3 G (respectively 1 G) have been reached for surface-averaged longitudinal magnetic field measurements for Am (respectively HgMn) stars. Associated with the results obtained previously for Ap/Bp stars, our study confirms the existence of a magnetic dichotomy among A-type stars. Our data demonstrate that there is at least one order of magnitude difference in field strength between Zeeman detected stars (Ap/Bp stars) and non Zeeman detected stars (Am and HgMn stars). This result confirms that the spectroscopically-defined Ap/Bp stars are the only A-type stars harbouring detectable large-scale surface magnetic fields.

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M. Auriere, G. A. Wade, F. Lignieres, A. Hui-Bon-Hoa, J. D. Landstreet, I. Iliev, J. -F. Donati, P. Petit, T. Roudier, S. Theado. 2010-08-18. No detection of large-scale magnetic fields at the surfaces of Am and HgMn stars. https://doi.org/10.1051/0004-6361/201014848

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