Speaker
Description
Convective velocity fields in the solar photosphere are strongly modified by magnetic structures such as faculae, leading to measurable changes in spectral line shapes and shifts. These effects become increasingly complex away from the disk center. Accurately capturing this center-to-limb variation is essential for interpreting spatially resolved solar observations and for modeling unresolved stellar spectra.
In this work, we investigate the convective velocity fields in radiative magnetohydrodynamic simulations of the quiet Sun harboring a small scale dynamo and of the facular regions, computed with the MURaM code. Employing these simulated atmospheres in the MPS-ATLAS radiative transfer code, we synthesize emergent spectra for 50 selected iron lines over a range of viewing angles from disk center to the limb. From these synthetic spectra we derive the center-to-limb variation of the spectral line shifts induced by convective flows. We validate the results for the quiet Sun by comparing them to disk-resolved quiet solar spectral measurements from the Institute for Astrophysics and Geophysics (IAG). This comparison with IAG provides a quantitative assessment of how accurately the simulations represent the convective velocities in the solar photosphere.
We further explore how the modification of vertical and horizontal convective flows by facular magnetic fields impacts the resulting spectral line profiles. We show that horizontal flows play an increasingly important role towards the limb and are crucial for understanding the spectral response to magnetoconvection away from disk center. We provide detailed predictions for the center-to-limb variation of spectral line shifts and asymmetries induced by faculae. A direct validation of these predictions through comparison with disk-resolved observations from the Sunrise-III mission is planned as a next step.