  Light curves produced by the Kepler mission demonstrate stochastic brightness
fluctuations (or "flicker") of stellar origin which contribute to the noise
floor, limiting the sensitivity of exoplanet detection and characterization
methods. In stars with surface convection, the primary driver of these
variations on short (sub-eight-hour) timescales is believed to be convective
granulation. In this work, we improve existing models of this granular flicker
amplitude, or $F_8$, by including the effect of the Kepler bandpass on measured
flicker, by incorporating metallicity in determining convective Mach numbers,
and by using scaling relations from a wider set of numerical simulations. To
motivate and validate these changes, we use a recent database of convective
flicker measurements in Kepler stars, which allows us to more fully detail the
remaining model--prediction error. Our model improvements reduce the typical
misprediction of flicker amplitude from a factor of 2.5 to 2. We rule out
rotation period and strong magnetic activity as possible explanations for the
remaining model error, and we show that binary companions may affect convective
flicker. We also introduce an "envelope" model which predicts a range of
flicker amplitudes for any one star to account for some of the spread in
numerical simulations, and we find that this range covers 78% of observed
stars. We note that the solar granular flicker amplitude is lower than most
Sun-like stars. This improved model of convective flicker amplitude can better
characterize this source of noise in exoplanet studies as well as better inform
models and simulations of stellar granulation.
