Speaker
Description
Radial velocity (RV) searches for small exoplanets around Sun-like stars are increasingly limited by activity-driven RV jitter. In stars with near-solar magnetic activity, bright faculae dominate this variability, yet their disk-integrated RV impact is poorly constrained. In this study, we measure their spectroscopic imprint with a physically consistent forward model, using the Sun as a testing bed.
We compute high-resolution synthetic spectra for a grid of viewing angles using the MPS-ATLAS radiative transfer code and 3D radiative MHD MURaM simulations of the quiet Sun and faculae. We then model the transit of a simple facular patch at the solar equator as the Sun rotates and analyse its signatures in a small sample of disk-integrated FeI and FeII line profiles.
Our results reveal that the strongly μ-dependent suppression of convective blueshift by faculae leads to characteristic RV profiles. Near disk centre the signal is dominated by reduced vertical blueshift, yielding a relative redshift, whereas toward the limb horizontal inflows into facular flux tubes and the enhanced weight of the approaching hot wall produce a relative blueshift despite foreshortening. We find that stellar rotation introduces asymmetry and shifts the RV extrema in phase, producing a facular-transit phase lag that is observed on the Sun and varies from line to line. RV amplitudes depend strongly on both line strength and ionisation stage, with the largest signals generally found for FeII lines and for weaker lines in both FeI and FeII.
Even a single facular region can therefore generate complex, position- and line-dependent RV signatures, motivating line-by-line RV extraction and activity-informed line weighting for extreme-precision RV surveys.