| Presenter: | Daniel Mueller |
| Affiliation: | European Space Agency |
| Title: | The multi-component field topology of sunspot penumbrae -- A diagnostic tool for spectropolarimetric measurements |
| Authors: | D.A.N. Mueller, R. Schlichenmaier |
| Form: | talk |
| Abstract: | Sunspots exhibit complex, highly structured magnetic fields and flows. Disentangling the atmospheric structure of sunspots is a great challenge, and can only be achieved by the combination of spectropolarimetry at high spatial resolution and detailed forward modeling. Detailed forward modeling is necessary for at least two reasons: On the one hand, it gives insight into the sensitivity of various spectral lines to different physical scenarios. On the other hand, it is a very useful tool to guide inversion techniques. In this work, we present a generalized 3D geometrical model that embeds an arbitrarily shaped flux tube in a stratified magnetized atmosphere. The new semi-analytical geometric model serves as a frontend for a polarized radiative transfer code. The advantage of this model is that it preserves the discontinuities of the physical parameters across the flux tube boundaries. This is important for the detailed shape of the emerging Stokes profiles and the resulting net circular polarization (NCP). We have applied the new model to recent spectropolarimetric observations and obtain the following results: (a) The inclination of downflows in the outer penumbra must be shallower than approximately 15 degrees; (b) observing the limb-side NCP of sunspots in the Fe~{\sc{i}} 1564.8~nm line offers a promising way to identify a reduced magnetic field strength in flow channels; (c) the choice of the background atmosphere can significantly influence the shape of the Stokes profiles, but does not change the global characteristics of the resulting NCP curves for the tested atmospheric models. The new model has also been successfully used to study NCP maps as a means of measuring the magnetic field of sunspots that allows a very high data compression given an overall spatial coherence of the field. This technique is well suited for the upcoming Solar Orbiter satellite, which will have very restricted telemetry during extended phases of the mission. |
| Session: | 4. Polarized radiative transfer, theory and modeling |
| Presentation date: | Tuesday 18th September |
| Presentation time: | 17:00:00 |