A magnetic confinement versus rotation classification of massive-star magnetospheres
Petit, V. ( Department of Geology & Astronomy, West Chester University, West Chester, PA 19383, USA; ); Owocki, S. P. ( Department of Physics & Astronomy, University of Delaware, Bartol Research Institute, Newark, DE 19716, USA ); Wade, G. A. ( Department of Physics, Royal Military College of Canada, PO Box 17000, Stn Forces, Kingston, ON K7K 7B4, Canada ); Cohen, D. H. ( Department of Physics & Astronomy, Swarthmore College, Swarthmore, PA 19081, USA ); Sundqvist, J. O. ( Department of Physics & Astronomy, University of Delaware, Bartol Research Institute, Newark, DE 19716, USA ); Gagné, M. ( Department of Geology & Astronomy, West Chester University, West Chester, PA 19383, USA ); Maíz Apellániz, J. ( Instituto de Astrofísica de Andalucía-CSIC, Glorieta de la Astronomía s/n, E-18008 Granada, Spain ); Oksala, M. E. ( Astronomický ústav, Akademie věd České republiky, Fričova 298, CZ-251 65 Ondřejov, Czech Republic ); Bohlender, D. A. ( National Research Council of Canada, Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada ); Rivinius, T. ( ESO - European Organization for Astronomical Research in the Southern Hemisphere, Casilla 19001, Santiago 19, Chile ); Henrichs, H. F. ( Astronomical Institute Anton Pannekoek, University of Amsterdam, Science Park 904, NL-1098 XH Amsterdam, the Netherlands ); Alecian, E. ( LESIA, Observatoire de Paris, CNRS UMR 8109, UPMC, Université Paris Diderot, 5 place Jules Janssen, F-92190 Meudon, France ); Townsend, R. H. D. ( Department of Astronomy, University of Wisconsin-Madison, 475 N Charter Street, Madison, WI 53706, USA ); ud-Doula, A. ( Penn State Worthington Scranton, Dunmore, PA 18512, USA ); MiMeS Collaboration ( Penn State Worthington Scranton, Dunmore, PA 18512, USA ) and 5 coauthors show affiliations
Monthly Notices of the Royal Astronomical Society, Volume 429, Issue 1, p.398-422
Published in Feb 2013
Building on results from the Magnetism in Massive Stars (MiMeS) project, this paper shows how a two-parameter classification of massive-star magnetospheres in terms of the magnetic wind confinement (which sets the Alfvén radius RA) and stellar rotation (which sets the Kepler co-rotation radius RK) provides a useful organization of both observational signatures and theoretical predictions. We compile the first comprehensive study of inferred and observed values for relevant stellar and magnetic parameters of 64 confirmed magnetic OB stars with Teff ≳ 16 kK. Using these parameters, we locate the stars in the magnetic confinement-rotation diagram, a log-log plot of RK versus RA. This diagram can be subdivided into regimes of centrifugal magnetospheres (CM), with RA 〉 RK, versus dynamical magnetospheres (DM), with RK 〉 RA. We show how key observational diagnostics, like the presence and characteristics of Hα emission, depend on a star's position within the diagram, as well as other parameters, especially the expected wind mass-loss rates. In particular, we identify two distinct populations of magnetic stars with Hα emission: namely, slowly rotating O-type stars with narrow emission consistent with a DM, and more rapidly rotating B-type stars with broader emission associated with a CM. For O-type stars, the high mass-loss rates are sufficient to accumulate enough material for line emission even within the relatively short free-fall time-scale associated with a DM: this high mass-loss rate also leads to a rapid magnetic spindown of the stellar rotation. For the B-type stars, the longer confinement of a CM is required to accumulate sufficient emitting material from their relatively weak winds, which also lead to much longer spindown time-scales. Finally, we discuss how other observational diagnostics, e.g. variability of UV wind lines or X-ray emission, relate to the inferred magnetic properties of these stars, and summarize prospects for future developments in our understanding of massive-star magnetospheres.
Astronomy: circumstellar matter; stars: early-type; stars: fundamental parameters; stars: magnetic fields; stars: mass-loss; stars: rotation
arXiv: Astrophysics - Solar and Stellar Astrophysics
2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society