Speaker
Jorrit Leenaarts
Description
The He I 10830 line is a powerful diagnostic of upper chromospheric magnetic fields.
In this talk we present a theoretical investigation of the formation of the line
based on 3D radiation-MHD simulations and 3D non-LTE polarized radiative transfer.
The radiation-MHD simulation was performed with the Bifrost code. It includes
non-equilibrium ionisation of hydrogen and helium, which is of great importance for
the thermal structure of the upper chromosphere. We performed 3D non-LTE radiative
transfer with the Multi3D code to obtain synthetic 10830 images from he simulation,
and performed an additional polarised radiative transfer step including the Hanle and
Zeeman effect using the Hazel code. We show that the spatial structure seen in 10830
images is caused by a combination of the structure of the UV radiation emitted in the
transition region and the density variations in the chromosphere. In addition we
discuss the strength and structure of the resulting polarisation signal.
