[Astronomy seminar] Astronomy seminar Friday 19/10 at 10:30 in FC61

[Astronomy seminar announcements]

Speaker: Johan Pires Bjørgen (Inst. for Solar Physics, Dept. of 
Astronomy, SU)

When/where: Friday October 19 at 10:30 in FC61 (Astronomy corridor, 6th 
floor)

Title: The synthetic chromosphere

Abstract:
The solar chromosphere is a dynamic layer between the photosphere and 
corona. Only few and complex spectral lines can probe the chromosphere 
making its observations a real challenge. To gain insight into the 
chromospheric physical conditions, we can compare the observations with 
3D radiation-magnetohydrodynamic models combined with forward modeling 
(radiative transfer). The chromospheric environment is strongly 
influenced by departures from local thermodynamic equilibrium (non-LTE), 
horizontal radiative transfer (3D effects), and partially-coherent 
scattering of photons (partial redistribution effects). All these 
effects make the detailed 3D non-LTE radiative transfer very 
computationally demanding. In this seminar, I will focus on the 
chromospheric resonance lines Ca II H&K. Understanding their formation 
is crucial to interpret the observations from the new imaging 
spectrometer CHROMIS, recently installed at the Swedish 1-m Solar 
Telescope. In our work, we modelled the Ca II H&K lines in 3D by using 
simulations of a quiet Sun and active region containing sunspots and a 
solar flare. For the quiet Sun, we investigated how the synthetic 
observables of Ca II H&K lines are related to atmospheric parameters. 
Aside from the theoretical interpretation of synthetic spectral lines, I 
will also discuss how to solve the non-local thermodynamic equilibrium 
radiative transfer problem more efficiently.

All welcome!