  Quasi-periodic modulations of the stellar light curve may result from dark
spots crossing the visible stellar disc. Due to differential rotation, spots at
different latitudes generally have different rotation periods. Hence, by
studying spot-induced modulations, one can learn about stellar surface
(differential) rotation and magnetic activity. Recently, Reinhold & Arlt (2015)
proposed a method based on the Lomb-Scargle periodogram of light curves to
identify the sign of the differential rotation at the stellar surface. Our goal
is to understand how the modulation of the stellar light curve due to the
presence of spots and the corresponding periodogram are affected by both the
stellar and spot properties. We generate synthetic light curves of stars with
different properties (inclination angle, limb darkening, and rotation rate) and
spot configurations (number of spots, latitude, intensity contrast, and size).
By analysing their Lomb-Scargle periodograms, we compute the ratio between the
heights of the second and first harmonics of the rotation period
(peak-height-ratio). We find that the peak-height ratios are essentially a
function of a single parameter, the fraction of time the spot is visible, which
is related to the sinusoidality of the spot modulation. We identify the
conditions under which the periodogram analysis can actually provide an
estimate of the spot latitudes and/or the stellar inclination angle. We also
identify possible sources of error in the identification of the sign of the
differential rotation.
