Stellar magnetic fields and stellar spectra

The stellar atmosphere is the “surface” of stars where starlight has its origin: they are the windows to the stars and are responsible for most of the information astronomers have of the cosmos. Magnetic fields are ubiquitous on stars but how they affect the structure and appearance of stars is still very poorly known.

The atmospheres of stars like the Sun are highly dynamical regions whose physical and thermal structures are shaped by the energy exchange between radiation and matter as well as by convective gas flows occurring in the stars. Thanks to supercomputers it is now possible to model stellar atmospheres and the emergent radiation to an unprecedented level of detail by means of realistic three-dimensional (3D), time-dependent, hydrodynamical computer simulations, an approach pioneered by our group at ANU.

Many stars are known to harbour magnetic fields that alter the physical structure of the stellar atmospheres and affect the emitted radiation. In the Sun, these magnetic fields are manifested as for example sunspots and active regions and are ultimately responsible for dynamical processes like flares and heating the solar chromosphere and corona. The role played by magnetic fields in stars is however still largely unknown both theoretically and observationally. Now is the ideal time to extend our world-leading 3D hydrodynamical stellar modeling to include magnetic effects.

In this project, you will study the impact of magnetic fields with different strengths and configurations on the physical structures of stellar atmospheres with a range of stellar parameters and compositions. You will also study how the magnetic fields affect the formation of stellar spectra. To carry out the project, you will employ state-of-the-art numerical codes for 3D radiative magneto-hydrodynamical simulations and 3D radiative transfer as well as have access to first-rate supercomputing facilities. 

The figure above shows the gas entropy in a simulated volume of the outer stellar layers of a red giant star. Red and orange indicate hot, high-entropy gas. The pattern visible at the surface of the simulation with large patches of hot gas enveloped in a network of cold gas is the characteristic fingerprint of stellar surface convection.
 

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