Institute of Astrophysics, University of Göttingen
We describe a study on spectropolarimetry of sunpot penumbrae. On the one hand, the study is focused on the analysis of 2D spectropolarimetric data observed with very high spatial resolution and, on the other hand, on the synthesis of Stokes profiles by means of numerical simulations of the penumbral atmosphere through a two-component atmopsheric model. Comparisons of the line-of-sight component velocities with the intensity maps in the whole sunspot area show that on the centre-side penumbra the Evershed flow (radial outflow of gas, Evershed 1909) is carried by bright filaments while on the limb side it is carried by dark filaments. The observations also confirm the un-combed structure of the magnetic field. To explain the picture about the penumbral fine structure seen in the observations we compare, in a first approximation, the observed Stokes profiles with synthetic ones. For the synthesis of Stokes profiles by solving the radiative transfer problem, we have considered a penumbral model with two components: a magnetic flux tube embedded in a static penumbral background. The asymmetries observed in penumbral grains, in the inner penumbra close to the umbra, can be reproduced by considering a vertical magnetic upflow of material hotter than the background.
PDF (0.8MB)Institute of Theoretical Physics, Technical University of Braunschweig
Similarly to the magnetized planets of the solar system, giant exoplanets are expected to be strong nonthermal radio emitters. This is especially true for close-in giant exoplanets ("Hot Jupiters"), where the interaction of the planet with the stellar wind is believed to be much stronger than for planets at larger orbital distances. Also, radio detection would yield additional information about the emitting planet, turning the search for radio emission from extrasolar planets into a useful additional observation method. Different parameters defining the expected exoplanetary radio flux are reviewed and discussed. It is shown that for certain planets the anticipated radio flux is strong enough to allow ground-based detection in the near future.
PDF (0.2MB)Max Planck Institute for Solar System Research
Based on 33 of the Galileo orbits energetic particle and magnetic field properties in the transition region between the dipolar and the current sheet region of the Jovian magnetosphere are determined. The prime focus of the work is on the analysis and interpretation of the electron pitch angle distribution (PAD).
The relation between the electron PAD boundary and the secondary auroral oval, a discrete feature observed equatorward of the main auroral oval is then discussed. Magnetic field models are used to trace field lines threading the boundary in the equatorial plane, to the Jovian ionosphere. The study of the electron PAD boundary in the equatorial plane is further developed by simulating electron pitch angle distribution changes under the assumption of adiabatic motion in order to explain the observed distributions. Furthermore the possibility of whistler wave generation as an important electron scattering mechanism leading to pitch angle diffusion is discussed.
The resulting precipitation fluxes are estimated and compared to the auroral observations. It is concluded that the PAD boundary is the magnetospheric source region of the secondary auroral oval.
PDF (0.5MB)Max Planck Institute for Solar System Research
On Mars young volcanism, tectonic activity and strong geoid anomalies are concentrated in only one region, the Tharsis bulge. These observations lead to the hypothesis that the thermal convection pattern in the martian mantle differs from that in Earth and is dominated by a few or maybe only a single strong plume under the Tharsis region.
A convection pattern with a strong reduced number of plumes can be observed in numerical models for Mars that include the endothermic phase transition from gamma-spinel to perovskite which may appear in Mars close to the core-mantle boundary.
In refined three-dimensional spherical convection models we investigate the thermal evolution of the martian mantle including its secular cooling. In these models the viscosity is depth dependent and is controlled by the horizontally averaged temperature through an Arrhenius law. The radial viscosity profile changes with time and in particular the growth of lithospheric thickness with time can be modelled in this way. In addition the depth dependence of the thermal expansivity and the depth and temperature dependence of the thermal conductivity are taken into account and their effects on the convection pattern and the thermal evolution are investigated. The temperature at the core-mantle boundary is time dependent and its variation is controlled by the heat flux from the core to the mantle. The model history of core temperature and heat flow allows to draw inferences on the existence and ultimate demise of a martian dynamo.
PDF (0.3MB)Max Planck Institute for Solar System Research
Magnetic flux emergence is associated with much of the dynamic phenomena observed in the solar atmosphere. The emergence is the passage of flux through the photosphere. This is the region where radiation becomes the dominant form of energy transport. In order to understand the emergence process, it is necessary to consider the effects of both magneto-convection and radiation. We have carried out 3D radiative magnetohydrodynamics (MHD) simulations to address this question. Having included the relevant physics, we directly compare the simulation results with observations.
PDF (0.6MB)