A New Model of Granulation-Driven Flicker in Kepler Light Curves

The light curves produced by the Kepler mission demonstrate real, stochastic brightness fluctuations (or "flicker") which contribute to the noise floor limiting the sensitivity of exoplanet detection and characterization methods. In stars with outer convective envelopes, the primary driver of these variations on shorter (sub-eight-hour) timescales is convective granulation. We have improved upon existing efforts to model this granular flicker by incorporating a wider set of scaling relations from numerical simulations, adding a correction factor for the effect of the Kepler bandpass, and incorporating metallicity in determining Mach numbers. In validating this model, we draw upon an expanded database of convective flicker measurements in Kepler stars, allowing us to more fully detail the remaining errors in model predictions. We introduce an "envelope" model which accounts for some of the spread in numerical simulations by producing a range of predicted flicker values for any one star, and we find that nearly 70% of observed stars fall within this range. We rule out rotation period and strong magnetic activity as possible explanations for the remaining model error. We also note that the solar granular flicker amplitude, measured in SOHO/Virgo data, is lower than most Sun-like stars. This progress toward an improved understanding of convective flicker can better characterize this source of noise in exoplanet detection and characterization as well as better inform models of stellar granulation.