[Astronomy seminar] Astronomy seminar TODAY 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!