Sensitivity of spectral lines to granulation: the Sun

The intrinsic variability of stars, due to acoustic oscillations, surface granulation, and magnetic activity, introduces radial velocity (RV) jitter in spectral lines, obscuring true planetary signals and hindering the detection of Earth-like planets. Granulation is particularly challenging, as it affects even the most inactive stars, introducing substantial signals, with amplitudes up to 1 m s−1. Disentangling granulation-induced RV jitter from the signal caused by planetary reflex motion requires reliable models of stellar granulation. In this study, we present a new approach for calculating the sensitivities of spectral lines to granulation. We simulate near-surface convection with the 3D radiative MHD code MURaM and calculate high-resolution emergent spectra with the radiative transfer code MPS-ATLAS. We then show that the spatial and temporal variability of spectral lines due to granulation are almost identical, and introduce a novel methodology that uses spatial variability at a single moment in time to compute their temporal variability. This approach significantly reduces computational costs. We apply our approach to analyze the response of lines from neutral and singly ionized elemental species to solar granulation. We find a clear distinction between the two groups of lines: those from neutral elements tend to show stronger variations in line strength, whereas those from singly ionized elements exhibit larger variations in central wavelength. These results enable the development of spectral line masks tailored to granulation sensitivity, offering a promising strategy to reduce granulation-induced RV noise and improve exoplanet detection.