Contributed Talk - Splinter Solar

Wednesday, 23 September 2020, 17:09   (virtual room L)

Weak field approximation magnetic field diagnostic using Mg I b line

Dusan Vukadinovic, Ivan Milic
Max Plank Institute for Solar System Research, University of Colorado Boulder

High spatial resolution solar spectropolarimetric observations usually focus either on photospheric (Fe 6300, Fe 5250, etc.) or on chromospheric (Ca II 8542, Ca II H & K) spectral lines. The lines that probe layers in between (e.g. Sodium D, Mg I b), are not studied so extensively, but that is about to change with upcoming instruments and telescopes. In this contribution we study the spectral region around Mg I b spectral line and it's diagnostic potential for estimating line-of-sight (LOS) magnetic field in photosphere and temperature minimum region. We first create a realistic model atom to properly model Mg I b spectral line and synthesize simulated Stokes spectra from a MuRAM quiet Sun simulation. We find excellent agreement between the mean synthetic spectra and the observed one. We then apply weak field approximation individually to Mg I b and nearby photospheric lines (Ti and Fe) and compare obtained magnetic field maps to the original MuRAM atmosphere. We find that Ti and Fe lines probe middle photosphere, while Mg I b probes the temperature minimum. We then apply the weak-field approximation to another set of synthetic data and find good agreement. To validate these results, we also derive an expression for the response functions of the weak-field estimation of the magnetic field and discuss their shapes and implications.