Project H

Imaging Spectropolarimetry of Quiet Sun Magnetic Fields

apl. Prof. Dr. Carsten Denker (AIP, advisor) and Dr. Thorsten Carroll (AIP, co-advisor)


Background: Measuring solar velocity and magnetic fields at the highest spatial, temporal, and spectral resolution needs a new generation of telescopes with post-focus instruments specifically tailored towards observing the fundamental scales of MHD processes given by the pressure scale height, the photon mean-free path length, and the fundamental magnetic structure size. Imaging spectroscopy and polarimetry can serve these needs, especially in combination with adaptive optics and advanced image restoration techniques.

Aims: The interaction between plasma flows and magnetic fields on the Sun is ultimately linked to fundamental questions such as (1) how are magnetic fields generated and dissipated, (2) what is the role of small-scale magnetic elements in the recently discovered local dynamo action on the surface of the Sun, and (3) how are flux tubes – the building blocks of solar and stellar magnetic fields – assembled into larger structures such as sun- or starspots?

Methods: AIP operates the GREGOR Fabry-Pérot Interferometer (GFPI) [33] at the new 1.5-meter GREGOR solar telescope [34], which will pass through science verification in 2012. The doctoral student will use MHD simulations (e.g., CO5BOLD [32]), compute synthetic Stokes line profiles [35], include realistic instrument profiles (including contributions by seeing and AO-correction), and compare these spectra to GFPI observations to study the effects of non-simultaneous spectral information. The finite time to acquire images at several wavelength positions is one of the challenges that imaging spectropolarimetry faces [36], another one is presented by the hundreds of millions of full-Stokes spectra acquired per observing day. Here, the student will adapt a spectral inversion code utilizing neural networks [37] to extract the 3-D magnetic field information from GFPI data in a time span comparable to the observations themselves.