Current projects

Only 20% of old field stars have detectable debris discs, leaving open the question of what disc, if any, is present around the remaining 80%. Young moving groups allow to probe this population, since discs are expected to have been brighter early on. This study considers the population of F stars in the 23Myr-old BPMG where we find that 9/12 targets possess discs. We also analyse archival ALMA data to derive radii for 4 of the discs, presenting the first image of the 63au radius disc of HD164249. Comparing the BPMG results to disc samples from ∼45Myr and ∼150Myr-old moving~groups, and to discs found around field stars, we find the disc incidence rate in young moving groups is comparable to that of the BPMG and significantly higher than that of field~stars. The BPMG discs tend to be smaller than those around field~stars. However, this difference is not statistically significant due to the small number of targets. Yet, by analysing the fractional luminosity vs disc radius parameter space we find that the fractional luminosities in the populations considered drop by two orders of magnitude within the first 100Myr. This is much faster than expected by collisional evolution, implying a decay equivalent to 1/age². We attribute this depletion to embedded planets which would be around 170 earth masses to cause a depletion on the appropriate timescale. However, we cannot rule out that different birth environments of nearby young clusters result in brighter debris discs than the progenitors of field~stars which likely formed in a more dense environment.

A paper showing the results can be found here

Debris discs are dusty belts of planetesimals around main-sequence stars, similar to the asteroid and Kuiper belts in our solar system. The planetesimals cannot be observed directly, yet they produce detectable dust in mutual collisions. Observing the dust, we can try to infer properties of invisible planetesimals. Here we address the question of what is the best way to measure the location of outer planetesimal belts that encompass extrasolar planetary systems. A standard method is using resolved images at mm-wavelengths, which

reveal dust grains with sizes comparable to the observational wavelength. Smaller grains seen in the infrared (IR) are subject to several

non-gravitational forces that drag them away from their birth rings, and so may not closely trace the parent bodies. In this study, we examine whether imaging of debris discs at shorter wavelengths might enable determining the spatial location of the exo-Kuiper belts with sufficient accuracy. We find that around M-type stars the dust best visible in the mid-IR is efficiently displaced inward from their birth location by stellar winds, causing the discs to look more compact in mid-IR images than they actually are. However, around

earlier-type stars where the majority of debris discs is found, discs are still the brightest at the birth ring location in the mid-IR regime. Thus, sensitive IR facilities with good angular resolution, such as MIRI on JWST, will enable tracing exo-Kuiper belts in nearby debris disc systems. 

A paper showing the results for thermal emission can be found here.

In this project, I write/use a code based on the ideas of Lee & Chiang 2016 where the radiation pressure of the host star influences the orbits of small dust particles. It is a collaboration with colleagues from Berkley. The code calculates the orbit of each grain and thus, generates an image of the whole disc. It is possible to generate both, scattered light and thermal emission images for a desired wavelength. In the near future it will be possible to use a planet as a perturber of the grains. Hence, I hope that I will be able to analyse disc structures and get an impression of the influence of planet-disc interactions.

Here, you will find a brief synopsis of my PhD-thesis (Doktorarbeit) .  The whole thesis can be read under Doktorarbeit. 

The SEDs of a sample of 39 Herschel-resolved debris discs were fitted with a newly implemented simulated annealing tool. It was the largest sample of resolved discs analysed so far. By inferring the disc radii from resolved images, the degeneracy between radial and grain parameters could be broken. Several dust materials were used for fitting, as well as different fitting models (modified blackbody, size distribution). The fitting results, such as minimum grain size and disc temperature of the cold dust components, were analysed statistically and several correlations between the stellar and fitting parameters could be found. One of the strongest correlations was the minimum to blowout grain size ratio as a function of stellar luminosity. In order to explain this trend, different possibilities were investigated, such as varying the dust material, analysing outliers and subsamples or taking the role of the surface energy or of the stirring level into account. In addition, the correlation found between disc to blackbody radius and stellar luminosity was applied to unresolved discs helping to infer the radii of unresolved discs.