X-ray emission from massive stars with magnetic fields

L.M. Oskinova1, W.-R. Hamann1 J.P. Cassinelli2, J.C. Brown3, H. Todt1,

1 Institute for Physics and Astronomy, University of Potsdam, 14476 Potsdam, Germany
2 Department of Astronomy, University of Wisconsin-Madison, Madison, WI 53711, USA
3 School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, UK

We investigate the connections between the magnetic fields and the X-ray emission from massive stars. Our study shows that the X-ray properties of known strongly magnetic stars are diverse: while some comply to the predictions of the magnetically confined wind model, others do not. We conclude that strong, hard, and variable X-ray emission may be a sufficient attribute of magnetic massive stars, but it is not a necessary one. We address the general properties of X-ray emission from "normal" massive stars, especially the long standing mystery about the correlations between the parameters of X-ray emission and fundamental stellar properties. The recent development in stellar structure modeling shows that small scale surface magnetic fields may be common. We suggest a "hybrid" scenario which could explain the X-ray emission from massive stars by a combination of magnetic mechanisms on the surface and shocks in the stellar wind. The magnetic mechanisms and the wind shocks are triggered by convective motions in sub-photospheric layers. This scenario opens the door for a natural explanation of the well established correlation between bolometric and X-ray luminosities.

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