Speaker
Description
Faculae are a major source of spectral and radial velocity (RV) variability in the Sun and in Sun-like stars, yet their disk-integrated spectroscopic imprint remains insufficiently constrained. We investigate how faculae modify spectral line morphology and line-of-sight velocity signatures from disk centre to the limb using a physically consistent forward model based on 3D radiative magnetohydrodynamic simulations with MURaM and spectral synthesis with MPS-ATLAS. We compute high-resolution spectra for a range of viewing angles and model the transit of a facular patch across the visible solar disk. We find that the facular signatures depend strongly on its position on the solar disk. Near disk centre, facular magnetic fields suppress the convective blueshift and produce a redshift relative to the quiet Sun. Towards the limb, faculae produce a relative blueshift, associated with the effect of faculae on the horizontal flows and the visibility of these flows. In combination with solar rotation, this centre-to-limb behaviour produces asymmetric RV profiles and a phase lag between the RV maxima and central meridian passage of the facular patch. Different spectral lines respond differently to these effects, showing that facular signatures are intrinsically line dependent. This highlights the diagnostic value of line-resolved spectroscopy for tracing facular magnetoconvection and for developing methods to mitigate their imprints in RV measurements. Observations of faculae at different disk positions from SUNRISE III provide a unique opportunity to verify this predicted centre-to-limb dependence of faculae-induced RV signals and to evaluate their relevance for stellar RV studies.