Some suggestions for possible Bachelor topics

If you find any of the below topics appealing, please contact me directly. Be aware that I can only supervise up to two bachelor students at the same time.

Topic 1: Modelling of specific colliding-wind binary systems (together with K. Reitberger)
We have investigated generic massive-star colliding-wind binary systems via numerical simulations in several studies. In these simulations, we modelled both, the fluid dynamics of the interacting stellar winds and the particles accelerated in these systems: the interacting stellar winds lead to an extended wind-collision region that is bounded by strong shocks on either side. At these shocks energetic particles are accelerated that subsequently can produce radio, x-ray, and possibly gamma-ray emission. In our study, we modelled both the particle spectra and the ensuing emission from these generic systems. So far, however, no specific colliding-wind binary system has been modelled by our group. The possible bachelor thesis, is to repeat and evaluate the simulations for a specific binary system that has been observed in a range of wavelengths. A possible system, that has been studied in great detail, is WR 140, thus, giving the opportunity to relate simulation results to direct observations.

Topic 2: Galactic cosmic ray propagation models
We are modelling the propagation of Galactic cosmic rays via the numerical solution of the corresponding transport equation (our modelling efforts are also discussed here). The transport equation depends on several propagation parameters that describe the transport physics. The influence of several of these propagation parameters is still underinvestigated. A corresponding parameter space exploration can, therefore, be the aim of a possible bachelor thesis: by comparing model results using different values for one or several of the propagation parameters, the influence of these transport parameters can be quantified. As a particular example the influence of a Galactic bar on the cosmic-ray flux at different locations in the Galaxy can be examined.

Topic 3: Emission of thermal bremsstrahlung from colliding-wind binary systems (together with K. Reitberger)
In a recent study, we modelled the gamma-ray emission from colliding-wind binary systems via numerical simulations. In this study we investigated the different emission channels of energetic electrons and protons. In a plasma, however, also the thermal electrons are responsible for the emission of thermal bremsstrahlung from these systems. A possible topic is, therefore, the computation of the thermal bremsstrahlung emission component of these colliding-wind binary systems. For this, the plasma data for different colliding-wind binary systems will be provided. From this data the thermal bremsstrahlung emission can be computed together with resulting bremsstrahlung spectra and emission maps.

Topic 4: Numerical solver for magnetohydrodynamics
In our group we use the magnetohydrodynamics code Cronos for the simulation of different astrophysical systems. This code is based on a so-called semi-discrete finite-volume scheme. It would be very interesting to compare this scheme to other available numerical schemes. Thus, a possible bachelor thesis is to implement the MUSCL-Hancock scheme for one-dimensional hydrodynamical problems. For this, a detailed step-by-step description will be provided that needs to be implemented into the program code. This can then be compared to the original solver using several test cases.

Topic 5: A solver for the losses of energetic particles
In our study of particle acceleration in colliding-wind binary systems (see also topic 1), we use a semi-Lagrangian solver to describe energy gains and losses of the energetic particles. These solvers are usually optimised for a smooth variation of the dynamic variables in energy. Cosmic rays, however, rather show a power-law dependence on energy. Therefore, such a solver can be adapted by taking this energy dependence into account within the so-called reconstruction. Here, reconstruction refers to the process of computing point values of the dynamic variables at arbitrary positions from the given discrete set of values of the dynamic variables at a specific time. In a possible bachelor thesis, an alternative reconstruction is to be implemented and tested in comparison to the one used before. For this, the full solver together with simple test cases are provided.