Toward Mitigating Granulation RV Noise with GRASS: the GRanulation and Spectrum Simulator

Despite recent advances in extremely-precise radial velocity (EPRV) spectrographs, intrinsic stellar variability still poses a significant obstacle to the detection and characterization of Earth-mass exoplanets in their stars’ habitable zones. In addition to pulsations and magnetic activity, granulation in the atmospheres of Sun-like stars skews the shape of absorption lines, creating a persistent RV noise source on the order of a few tens of centimeters per second. To complement previous studies of granulation that have used computationally expensive magnetohydrodynamic (MHD) simulations, we have developed a synthetic spectrum generator that uses time- and disk-resolved observations of the Sun to efficiently generate synthetic time series of spectra. We present this tool, the GRanulation And Spectrum Simulator (GRASS; Palumbo et al. 2022; https://github.com/palumbom/GRASS), and use its output spectra to compare the results of RV measurement and analysis methods that operate on either full spectra or cross-correlation function (CCF) derived RVs. We further discuss additional use-cases of GRASS as a testing ground for methods designed to mitigate RV noise arising from granulation.