3D Models of stellar atmospheres and proto-planetary disks
Throughout their very long life-times, low-mass stars carry with them the chemical signatures of their birth place as they orbit the Galaxy. Deciphering these fingerprints on the observed spectrum by accurate determination of the chemical composition is one on the main challenges for any study of Galactic archaeology and stellar physics. In particular, the complex interplay between radiation and convection must be realistically captured by the stellar models to predict spectral line strength and shapes free from large systematic biases. This requires a full 3D treatment of gas dynamics coupled with radiative transfer. We will model detailed photospheric line-formation in the Sun and metal-poor stars to shed light on fundamental problems with the chemistry in the early Universe, as depicted by the nucleosynthesis of the Big Bang and the First Stars. In addition to studying the structure and evolution of old stars as described above, we also model the circumstellar environments of new-born stars, i.e. proto-planetary disks. These are critical for understanding the formation and properties of our own and other planetary systems. We perform full-scale modelling of the disks' internal structures and 3D radiation fields using custom 3D adaptions of a detailed 2D+ code (Woitke et al, 2009, A&A 501, 383). Such models are highly computationally expensive but allows us to produce high-resolution spectra for comparing models with observations. Finally, around ten percent of the intermediate-mass stars have very strong magnetic fields, and patchy surface distribution of some elements in their atmospheres whose concentrations can locally be thousands of times higher than normal. These conditions in their atmospheres lead to complex spectra that are variable on time scales of days. We apply 3D magnetic Doppler imaging (3D-MDI) to observations of these stars to reconstruct the magnetic field and produce maps of the chemical elements that show how their concentration changes across the surface of the star and with depth in the atmosphere. The results from this research, which has not been attempted before, will serve as the basis for future theoretical and observations studies.