(see Eq. \[eq:covariance\]) [@Angus2018]. The covariance function’s periodic timescale was a free parameter [$P_{\text{rot}}$]{} for which the posterior probability density function (PDF) was sampled using a Markov Chain Monte Carlo (MCMC) method (see Appendix \[sec:GP\]). We modeled each binned WASP light curve with a GP. We adopted a bin size of 1 day to reduce the computation time. In preliminary analyses, we also tested bin sizes of 0.25, 0.5, and 2 days and found that, probably due to the very large number of points, the recovered values of [$P_{\text{rot}}$]{} were not very sensitive to this choice.

After sampling the posterior PDFs of the GP hyperparameters, we arrived at point estimates of each parameter value based on the maximum a-posteriori values and 68 percent confidence intervals. The resulting mean GP model of the data from each WASP observing season is depicted in Fig. \[fig:WASPphot\] along with the corresponding $1\sigma$ confidence interval. Over the five observing seasons, the measured (median) rotation period of L 168-9 was [$P_{\text{rot}}$]{} $=29.8\pm 1.3$ days.

In principle, the WASP signal could have arisen from any star within the 48" extraction aperture. However, L 168-9 is by far the brightest star in the aperture. Another concern with any 