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Constraining general massive-star physics by exploring the unique properties of magnetic O-stars: Rotation, macroturbulence & sub-surface convection

Published online by Cambridge University Press:  23 January 2015

Jon O. Sundqvist
Jon O. Sundqvist*
Affiliation:
Universitätssternwarte, Scheinerstr. 1, D-81679 Müenchen; Germany email: [email protected]
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Abstract

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A quite remarkable aspect of non-interacting O-stars with detected surface magnetic fields is that they all are very slow rotators. This paper uses this unique property to first demonstrate that the projected rotational speeds of massive, hot stars, as derived using current standard spectroscopic techniques, can be severely overestimated when significant “macroturbulent” line-broadening is present. This may, for example, have consequences for deriving the statistical distribution of rotation rates in massive-star populations. It is next shown how such macroturbulence (seemingly a universal feature of hot, massive stars) is present in all but one of the magnetic O-stars, namely NGC 1624-2. Assuming then a simple model in which NGC 1624-2's exceptionally strong, large-scale magnetic field suppresses atmospheric motions down to layers where the magnetic and gas pressures are comparable, first empirical constraints on the formation depth of this enigmatic hot-star macroturbulence is derived. The results suggest it originates in the thin sub-surface convection zone of massive stars, consistent with a physical origin due to, e.g., stellar pulsations excited by the convective motions.

Keywords

stars: early-typestars: rotationstars: magnetic fieldsconvection
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 9 , Issue S307: New windows on massive stars: asteroseismology, interferometry, and spectropolarimetry , June 2014 , pp. 353 - 358
Copyright
Copyright © International Astronomical Union 2015 

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