Turbulent Conditions in the Atmospheres of Stars

PhD defence, Wednesday 24 January 2018, Magnus Johan Aarslev.

2018.01.24 | Trine Berndt Turtiainen Scheelke

Magnus Johan Aarslev

During his studies, Magnus Aarslev has conducted research into theoretical models of energy transport in solar-like stars with special focus on the implications for asteroseismology, where observations of acoustic oscillations in the surface of stars are used to derive important properties such as the stars' internal structure, age and chemical composition. Many stars pulsate with several frequencies simultaneously, because dynamical effects inside create soundwaves that travel through the stars. The principle is much like the more well-knowned concept of organ pipes, where the frequency of sound is dertermined by both the width and the length as well as  the temperature of the air and the material of which it is made. Similarly for pulsating stars, their oscillation frequencies tell us a lot about the way they are build and what goes on inside. In the outermost parts of pulsating stars, energy from the core is transported to the surface by turbulent convection and emitted as light that we can observe. This turbulence can interact with and affect the natural pulsations of the star. This makes it very complicated to calculate the oscillation frequencies of a star. By using advanced computer simulations of the dynamics in stellar atmospheres, Magnus Aarslev has worked on improving the theoretical convection models used in the to computations of the structure of stars , as well as their evolution and oscillation properties. It is a broad project that also focuses on exploring how modern simulations of stellar atmospheres can be utilized in asterosesimology. One of the main results is the successful modelling of observed, asteroseismic properties for a number of red giant stars observed with the Kepler satellite. The results contribute to our collective knowledge and understanding of giant stars, which also represent the next stage of evolution for the Sun.

The PhD degree was completed at the Stellar Astrophysics Centre, Department of Physics and Astronomy, Science and Technology, Aarhus University.

This résumé was prepared by the PhD student.

Time: Wednesday 24 January 2018 at 14.00
Place: Building 1523, room 318, Physics Auditorium, Department of Physics and Astronomy, Ny Munkegade 120, Aarhus University, 8000 Aarhus C.
Title of dissertation: Convection and stellar oscillations
Contact information: Magnus Johan Aarslev, e-mail: mja@phys.au.dk
Members of the assessment committee:
Professor Mário João Pires Fernandes Garcia Monteiro, Departamento de Matemática Aplicada, Faculdade de Ciências da Universidade do Porto, Portugal
Chargé de Recherche at CNRS Lionel Pascal Bigot, Université Côte D’Azur, Observatoire de la Côte d’Azur, CNRS, France
Associate Professor Georg Bruun (Chair), Department of Physics and Astronomy, Aarhus University
Main supervisor:
Professor Jørgen Christensen-Dalsgaard, Stellar Astrophysics Centre, Institut for Fysik og Astronomi, Aarhus Universitet
Language: The PhD dissertation will be defended in English

The defence is public.
The dissertation is available for reading at the Graduate School of Science and Technology/GSST,
Ny Munkegade 120, building 1520, rooms 128-134, 8000 Aarhus C.

PhD defence
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Revised 24.04.2018