Polar

Abstract: It is shown that the electric field at a particular nucleus arising from polar groups in other parts of a molecule can lead to chemical shifts proportional to the first power of the field strength....

Abstract: It is shown that the line-of-sight matching procedure involved in potential field models of the solar corona do not make good use of the available data because there is strong evidence that the magnetic field is nearly radial, and therefore nonpotential, at the photosphere. It is argued that the observed photospheric field should first be corrected for line-of-sight projection and then matched to the radial component of the potential field. It is shown that this procedure yields much stronger polar fields than the standard method and produces better agreement with high-latitude coronal holes and with white-light structures in the outer corona. The relationship of both methods to the observed inclination angles of polar plumes is also discussed.

Abstract: We present numerical magnetohydrodynamic (MHD) simulations of the effect of stellar dipole magnetic fields on line-driven wind outflows from hot, luminous stars. Unlike previous fixed-field analyses, the simulations here take full account of the dynamical competition between field and flow and thus apply to a full range of magnetic field strength and within both closed and open magnetic topologies. A key result is that the overall degree to which the wind is influenced by the field depends largely on a single, dimensionless wind magnetic confinement parameter η* (= BR/v∞), which characterizes the ratio between magnetic field energy density and kinetic energy density of the wind. For weak confinement, η* ≤ 1, the field is fully opened by the wind outflow, but nonetheless, for confinements as small as η* = 1/10 it can have a significant back-influence in enhancing the density and reducing the flow speed near the magnetic equator. For stronger confinement, η* > 1, the magnetic field remains closed over a limited range of latitude and height about the equatorial surface, but eventually is opened into a nearly radial configuration at large radii. Within closed loops, the flow is channeled toward loop tops into shock collisions that are strong enough to produce hard X-rays, with the stagnated material then pulled by gravity back onto the star in quite complex and variable inflow patterns. Within open field flow, the equatorial channeling leads to oblique shocks that are again strong enough to produce X-rays and also lead to a thin, dense, slowly outflowing disk at the magnetic equator. The polar flow is characterized by a faster-than-radial expansion that is more gradual than anticipated in previous one-dimensional flow tube analyses and leads to a much more modest increase in terminal speed (less than 30%), consistent with observational constraints. Overall, the results here provide a dynamical groundwork for interpreting many types of observations—e.g., UV line profile variability, redshifted absorption or emission features, enhanced density-squared emission, and X-ray emission—that might be associated with perturbation of hot-star winds by surface magnetic fields.