of the brightness fluctuations scales in inverse proportion to the square root of the number of convective cells on the surface of the star (we assume the cells are statistically independent; see also Ludwig 2006). The characteristic size of cells was assumed to scale with the product of the mixing length parameter and the isothermal scale height at the surface of the star. The brightness fluctuations associated with individual cells were assumed to scale with the surface velocities associated with the convection, which came from the stochastic excitation models that were used to predict the mode excitation and damping rates. To estimate the timescale of the granulation we assumed it scales in inverse proportion to the acoustic cut-off frequency of the star.

The standard deviation of the active region noise was assumed to scale with $R'_{\rm HK}$, in the manner described by Aigrain, Favata & Gilmore (2005). We also allowed for the effect of the angle of inclination of the star, having assumed the active-region signal was confined within certain bands of stellar latitude, using the work of Knaack et al. (2001) as a guide. We assumed the timescale of the active-region signal scaled with the period of rotation of 