This research investigates the structure and cause of sunspot penumbra. The investigators use an inversion of data that couple high spatial resolution, high spectral resolution, and the full polarization state of light from the solar photosphere. This inversion allows them to determine the vector magnetic field and the thermodynamic state in the line-forming region. Specifically, investigators compare and contrast two inversion techniques: one that allows multiple magnetic atmospheres and non-magnetic model atmosphere to contribute to the detected signal; the second, a procedure that allows for bulk gradients in the velocity field and magnetic vector within the model atmosphere. The more successful inversion procedure dictates which model applies to interpreting penumbral observations. Finally, the investigators answer how, why and when penumbrae form in sunspot evolution. Results from the research paint a more coherent physical picture of sunspot penumbrae, where knowledge has previously been limited, to attempt understanding magnetohydrodynamic phenomena in the sun (especially associated with sunspots).
