Theoretical astrophysics and plasma physics at RPC

Abstract:

The grating instruments on board Chandra and XMM-Newton now allow measurements of electron densities. These rely on the ratios of fluxes in emission lines, where one line depends on both collisional and radiative decay rates. The electron density is required to constrain the physical extent of the emitting region, and large samples of measurements are of interest in the context of trends in coronal activity. Here we discuss the important He I-like ions and the differences in densities that result when different current data bases are used.

Abstract:

Two issues are discussed. First, a new sheath model that takes into account charge-saturation is implemented in HPHall. Second, the transition between the quasineutral solution and the sheaths at the lateral walls is found to be treated deficiently in the original code. The use of finer meshes yields better solutions but do not solve the problem completely. Hall thrusters; particle-in-cell codes; sheaths.

Abstract:

Techniques for the construction of dynamical Galaxy models should be considered essential infrastructure that should be put in place before GAIA flies. Three possible modelling techniques are discussed. Although one of these seems to have significantly more potential than the other two, at this stage work should be done on all three. A major effort is needed to decide how to make a model consistent with a catalogue such as that which GAIA will produce. Given the complexity of the problem, it is argued that a hierarchy of models should be constructed, of ever increasing complexity and quality of fit to the data. The potential that resonances and tidal streams have to indicate how a model should be refined is briefly discussed.