Structure and dynamics of the solar corona and its roots on the solar surface

August 01, 2017
Open PhD Project Sun and Heliosphere

Analysing the solar extreme UV emission using space-based imaging and spectroscopy to unravel the thermal and magnetic properties of the upper solar atmosphere

During a total eclipse of the Sun the moon occults the disk of our star and the faint outer atmosphere of the Sun, the corona, becomes visible. The corona is composed of million Kelvin hot plasma that is fine-structured by the magnetic field rooted in magnetic concentrations on the surface of the Sun. This structuring by the magnetic field is best seen in images of the Sun in the extreme UV (see figure) or in X-rays that show the hot coronal plasma in coronal loops (Aschwanden & Peter 2017). Recent observations at unprecedented resolution show that magnetic reconnection at the footpoints of coronal loops plays a key role for plasma heating that has not been considered yet (Chitta et al. 2017). So far, most models concentrated on either wave heating or dissipation of currents, while there is clear evidence for reconnection events deep in the solar atmosphere (Peter et al. 2014). The overarching goal of this project is to investigate how the corona is supplied with mass and how the plasma is energized to reach high temperatures.

Magnetic structure at the footpoints of coronal loops revealed. The left panel shows the magnetic field as observed by IMaX/Sunrise at the footpoints of coronal loops seen by AIA/SDO in the right panel. While in general the loops are rooted on one side in a plage area dominated by one magnetic polarity (black), the footpoints of coronal loops (white circles) are found at places where also small parasitic opposite polarities (white) are present. This shows that small-scale reconnection plays a key role for the energization of coronal loops that is much more prominent than thought before.

To address the scientific questions, a combination of observational techniques will be used. For the analysis data from extreme UV imaging (mainly AIA/SDO and IRIS) and spectroscopy (mainly IRIS and EIS/Hinode) will be combined with magnetic field observations. The latter can be either at moderate resolution which is always available (HMI/SDO), or high-resolution magnetic maps of specific targets (acquired e.g. by ground-based observatories like Gregor). The spectroscopic data allow a detailed analysis of the density (through ratios of emission lines), the temperature (through an emission measure analysis), and the dynamics (through the line profiles). Combined with extreme UV imaging and magnetic field data from the solar surface this will provide insight in how the coronal loops respond to magnetic changes, in particular how and why loops become visible in the first place.

Further reading:

1.
P. Aschwanden, H. Peter, "The Width Distribution of Loops and Strands in the Solar Corona—Are We Hitting Rock Bottom?", ApJ 840, id4 (2017).
ADS DOI
L. P. Chitta, H. Peter, S. K. Solanki, P. Barthol, A. Gandorfer, L. Gizon, J. Hirzberger, T. L. Riethmüller, M. van Noort, J. Blanco Rodríguez, J. C. Del Toro Iniesta, D. Orozco Suárez, W. Schmidt, V. Martínez Pillet, and M. Knölker, "Solar Coronal Loops Associated with Small-scale Mixed Polarity Surface Magnetic Fields," Astrophysical Journal, Suppl. Ser. 229, 4 (2017).
MPG.PuRe
DOI
H. Peter, H. Tian, W. Curdt, D. Schmit, D. Innes, B. De Pontieu, J. Lemen, A. Title, P. Boerner, N. Hurlburt, T. D. Tarbell, J. P. Wuelser, Juan Martinez-Sykora, L. Kleint, L. Golub, S. McKillop, K. K. Reeves, S. Saar, P. Testa, C. Kankelborg, S. Jaeggli, M. Carlsson, and V. Hansteen, "Hot explosions in the cool atmosphere of the Sun," Science 346 (6207), 1255726 (2014).
MPG.PuRe
DOI

Find the papers in arXiv for free access.

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