Plasma injection into a solar coronal loop. (arXiv:1905.07800v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Li_L/0/1/0/all/0/1">Leping Li</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Peter_H/0/1/0/all/0/1">Hardi Peter</a>
Context. The details of the spectral profiles of extreme UV emission lines
from solar active regions contain key information to investigate the structure,
dynamics, and energetics of the solar upper atmosphere. Aims. We characterize
the line profiles not only through the Doppler shift and intensity of the bulk
part of the profile. More importantly, we investigate the excess emission and
asymmetries in the line wings to study twisting motions and helicity. Methods.
WeusearasterscanoftheInterfaceRegionImagingSpectrograph(IRIS)inanactive region.
We concentrate on the Si iv line at 1394 {AA} that forms just below 0.1 MK and
follow the plasma in a cool loop moving from one footpoint to the other. We
apply single-Gaussian fits to the line core, determine the excess emission in
the red and blue wings, and derive the red-blue line asymmetry. Results. The
blue wing excess at one footpoint shows injection of plasma into the loop that
is then flowing to the other side. At the same footpoint, redshifts of the line
core indicate that energy is deposited at around 0.1 MK. The enhanced pressure
would then push down the cool plasma and inject some plasma into the loop. In
the middle part of the loop, the spectral tilts of the line profiles indicate
the presence of a helical structure of the magnetic field, and the line wings
are symmetrically enhanced. This is an indication that the loop is driven
through the injection of helicity at the loop feet. Conclusions.
Iftheloopisdriventobehelical,thenonecanexpectthatthemagneticfieldwill be in a
turbulent state, as it has been shown by existing MHD models. The turbulent
motions could provide an explanation of the (symmetric) line wing enhancements
which have been seen also in loops at coronal temperatures, but have not been
understood so far.
Context. The details of the spectral profiles of extreme UV emission lines
from solar active regions contain key information to investigate the structure,
dynamics, and energetics of the solar upper atmosphere. Aims. We characterize
the line profiles not only through the Doppler shift and intensity of the bulk
part of the profile. More importantly, we investigate the excess emission and
asymmetries in the line wings to study twisting motions and helicity. Methods.
WeusearasterscanoftheInterfaceRegionImagingSpectrograph(IRIS)inanactive region.
We concentrate on the Si iv line at 1394 {AA} that forms just below 0.1 MK and
follow the plasma in a cool loop moving from one footpoint to the other. We
apply single-Gaussian fits to the line core, determine the excess emission in
the red and blue wings, and derive the red-blue line asymmetry. Results. The
blue wing excess at one footpoint shows injection of plasma into the loop that
is then flowing to the other side. At the same footpoint, redshifts of the line
core indicate that energy is deposited at around 0.1 MK. The enhanced pressure
would then push down the cool plasma and inject some plasma into the loop. In
the middle part of the loop, the spectral tilts of the line profiles indicate
the presence of a helical structure of the magnetic field, and the line wings
are symmetrically enhanced. This is an indication that the loop is driven
through the injection of helicity at the loop feet. Conclusions.
Iftheloopisdriventobehelical,thenonecanexpectthatthemagneticfieldwill be in a
turbulent state, as it has been shown by existing MHD models. The turbulent
motions could provide an explanation of the (symmetric) line wing enhancements
which have been seen also in loops at coronal temperatures, but have not been
understood so far.
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