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<div class="PlainText">Speaker: Johan Pires Bjørgen (Inst. for
Solar Physics, Dept. of <br>
Astronomy, SU)<br>
<br>
When/where: Friday October 19 at 10:30 in FC61 (Astronomy
corridor, 6th <br>
floor)<br>
<br>
Title: The synthetic chromosphere<br>
<br>
Abstract:<br>
The solar chromosphere is a dynamic layer between the
photosphere and <br>
corona. Only few and complex spectral lines can probe the
chromosphere <br>
making its observations a real challenge. To gain insight into
the <br>
chromospheric physical conditions, we can compare the
observations with <br>
3D radiation-magnetohydrodynamic models combined with forward
modeling <br>
(radiative transfer). The chromospheric environment is
strongly <br>
influenced by departures from local thermodynamic equilibrium
(non-LTE), <br>
horizontal radiative transfer (3D effects), and
partially-coherent <br>
scattering of photons (partial redistribution effects). All
these <br>
effects make the detailed 3D non-LTE radiative transfer very <br>
computationally demanding. In this seminar, I will focus on
the <br>
chromospheric resonance lines Ca II H&K. Understanding
their formation <br>
is crucial to interpret the observations from the new imaging
<br>
spectrometer CHROMIS, recently installed at the Swedish 1-m
Solar <br>
Telescope. In our work, we modelled the Ca II H&K lines in
3D by using <br>
simulations of a quiet Sun and active region containing
sunspots and a <br>
solar flare. For the quiet Sun, we investigated how the
synthetic <br>
observables of Ca II H&K lines are related to atmospheric
parameters. <br>
Aside from the theoretical interpretation of synthetic
spectral lines, I <br>
will also discuss how to solve the non-local thermodynamic
equilibrium <br>
radiative transfer problem more efficiently.<br>
<br>
All welcome!<br>
<br>
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