How an antenna launches its input power into radiation: the pattern of the Poynting vector at and near an antenna

In this paper I first address the question of whether the seat of the power radiated by an antenna made of conducting members is distributed over the ``arms'' of the antenna according to -J . E, where J is the specified current density and E is the electric field produced by that source. Poynting's theorem permits only a global identification of the total input power, usually from a localized generator, with the total power radiated to infinity, not a local correspondence of -J . E dv with some specific radiated power, r^2 S . n dO. I then describe a model antenna consisting of two perfectly conducting hemispheres of radius a separated by a small equatorial gap across which occurs the driving oscillatory electric field. The fields and surface current are determined by solution of the boundary value problem. In contrast to the first approach (not a boundary value problem), the tangential electric field vanishes on the metallic surface. There is no radial Poynting vector normal to the surface. Numerical examples are shown to illustrate how the energy flows from the input region of the gap and is guided near the antenna by its ``arms'' until it is launched at larger r/a into the radiation pattern determined by the value of ka.Comment: 24pages, 8 figures, submitted for publicatio

High-precision Atomic Physics Laboratories in Space: White Dwarfs and Subdwarfs

The 21st European Workshop on White Dwarfs was held in Austin, TX from July 23rd to 27th of 2018Stellar atmospheres are prime laboratories to determine atomic properties of highly ionized species. Reliable opacities are crucial ingredients for the calculation of stellar atmospheres of white dwarfs and subdwarfs. A detailed investigation on the precision of many iron-group oscillator strengths is still outstanding. To make progress, we used the Hubble Space Telescope Imaging Spectrograph to measure high-resolution spectra of three hot subdwarfs that exhibit extremely high iron-group abundances. The predicted relative strengths of the identified lines are compared with the observations to judge the quality of Kurucz’s line data and to determine correction factors for abundance determinations of the respective elements.Astronom