Spectroscopic light curve fitting of OB12. From left to right, the first panel: the raw light curves (circles) and the best-fit curves (solid lines); the second panel: the detrended light curves (circles) and the best-fit transit models (solid lines);the third panel: the extracted systematics (circles) and their GP models (solid lines); the fourth panel: the residuals. The points affected by the moving ghost have been removed. The curves were arbitrarily shifted for clarity.