[Astronomy seminar] Astronomy seminar Friday 26/10 at 10:30 in FC61

[Astronomy seminar announcements]

Speaker: Tine Libbrecht (Inst. for Solar Physics, Dept. of Astronomy, SU)

When/where: Friday October 26 at 10:30 in FC61 (Astronomy corridor, 6th 
floor)

Title: Exploring the diagnostic value of He I D3 in the solar chromosphere

Abstract:
The research question of my PhD is in a way a simple one: what can 
observations of the He I D3 line teach us about the solar chromosphere? 
This optical spectral line at 5876 Å is formed in the upper 
chromosphere, and is sensitive to the local magnetic field and to 
heating of the transition region and corona. In order to explain why, I 
will discuss the unconventional formation mechanism of He I D3. This 
line was a commonly used diagnostic for the solar chromosphere in the 
70's for flares and later also for prominences. However, the spatial 
resolution of the data available is very poor compared to what we can 
achieve today at for example the SST. During my PhD, I have focused on 
high-resolution observations of He I D3 with different instruments at 
the SST, and in co-observation with space-borne instruments. These 
observations have provided new insights in the reconnection events that 
we have studied. Our He I D3 observations have set constraints on the 
temperature of Ellerman Bombs (EBs, i.e. tiny reconnection events in the 
upper photosphere) - which is relevant in the context of chromospheric 
heating. Currently, 3D radiative transfer calculations are undertaken 
with the goal of understanding helium line formation in small-scale 
reconnection events. In the context of flares, we measured strong 
downflows in the chromosphere via He I D3, revealing shocks and dynamics 
during a flare. Spectro-polarimetry was used to measure the magnetic 
field during a flare and to propose its magnetic topology. In summary, 
the He I D3 line is an excellent probe for high-energy processes in the 
chromosphere and many possible applications are yet to be exploited.

All welcome!