Alumni 2023

    Ekaterina Magg   (Russia)                                                                                                                                       01.02.2023  

Constraining stellar physics with the NLTE radiative transfer  ( thesis pdf, 120 MB)

All chemical elements in the Universe, except the very few lightest species, are produced in a nuclear fusion inside the stars. Following the stellar life cycle, these chemical elements are expelled into the interstellar medium where they proceed to contribute to the chemical enrich- ment of their surroundings. Spectroscopic observations are currently the only way to infer the chemical make-up of the stars. Combining those with the physical modelling of the radiation in the stellar plasma allows us to detect and measure the number of chemical elements we all are made of. The approach is generally applied to individual stars constituting the larger scale populations, from clusters to galaxies including our Milky Way and beyond. In this thesis I focus on the non-equilibrium modelling of stellar radiation and its influence on the measured chemical abundances of various elements. I provide a general overview of the methods and necessary information used to infer the stellar chemical composition. I then present developments in the non-equilibrium modelling and apply it to the analysis of a star cluster, our host star – the Sun, and eventually a broader Galactic population. I focus on the opportunities our modelling approach presents to observationally constrain the stellar evolution and consequential enrichment of the Galactic populations.

Supervisor:    Maria Bergemann   (MPIA)

    Grigorii Smirnov-Pinchukov   (Russia)                                                                                                                     12.01.2023

Formylium as a tracer of circumstellar disks physics  ( thesis pdf, 26 MB)

There are many different tracers of circumstellar disk physics, most notably, micrometer to millimeter-sized dust, and one of the most abundant molecules, CO. Formylium (HCO+) is another commonly observed species. Its chemistry is more complex than CO chemistry, and more interpretation steps are necessary to build the bridge between the disk structure and observed emission. Its isotopologs DCO+ and H13CO+ complement the picture and allow a more precise understanding of the disk structure. In this thesis, I present my results achieved by combining and developing physical modeling, chemical kinetics, and radiative transfer methods to understand circumstellar disks' physical properties through formylium isotopologs observations. I explain the observed DCO+ increase in the protoplanetary disk gap and use it as proof of the reduced amount of gas in the gaps. I show that HCO+ should be the brightest molecule after CO isotopologs in the gas-rich debris disks, and its brightness would reveal the elemental composition, but a next-generation observatory is needed to detect it. Then I present an application of the machine learning approach to predict the modeled disk chemistry instantaneously based on the pre-computed disk models' data set, allowing the replacement of computationally expensive thermo-chemical models in the fitting pipelines. Finally, I demonstrate the data which will be analyzed using this approach.

Supervisor:    Thomas Henning  (MPIA)