Magnetic Channeling of Radiatively Driven Hot-Star Winds

Abstract

Abstract. Massive, hot, luminous stars have strong stellar winds driven by line-scattering of the star's continuum radiation. Spectropolarimetric observations have detected substantial large-scale dipole magnetic fields for several hot stars. This paper discusses our recent efforts to carry out MHD simulations of the effect of magnetic fields in channeling and confining the wind outflow, with particular emphasis on the "Magnetically Confined Wind Shock" (MCWS) paradigm for explaining the relatively hard X-ray emission observed by the Chandra X-ray observatory for magnetic hot stars like Theta 1 Ori C. We also examine the effect of magnetic fields on the wind from a rotating star, showing that this can spin-up the outflowing material, but does not readily form a Keplerian "Magnetically Torqued Disk". We further describe a new "Rigidly Rotating Magnetosphere"(RRM) model that has proven highly successful in reproducing the rotational modulated Balmer emission seen in magnetic Bp stars like sigma Ori C. We conclude with an outlook for the general role of magnetic fields in structuring hot-star mass loss and circumstellar matter.

Mass loss from hot massive stars

“…Field aligned rotation and the rigidly rotating magnetosphere model. In a followup study, ud-Doula et al (2008, see also Owocki et al 2005) included rotation (aligned with the magnetic field to avoid 3-D calculations) and investigated the question whether magnetic fields could spin up the stellar wind outflow into a "magnetically torqued disk", as suggested by Cassinelli et al (2002). The closed loops present for larger η * tend to keep the outflow in rigid body rotation (i.e., v φ (r) ∝ r), and it might be possible to propel material into a Keplerian disk if the Alfvén radius is somewhat larger than the Keplerian co-rotation radius, R K ≈ (v rot /v orb ) −2/3 R * , where rigid-body rotation would yield a balance between centrifugal and gravitational acceleration.…”