Results of the rotation period search for BD−21 1074A. Top panels: differential magnitude time series of BD−21 1074A and of CK−C (arbitrarily shifted in magnitude), where asterisks and bullets represent the un-averaged and averaged (2 h bin) data, respectively; L-S and Clean periodograms showing the power peak corresponding to the rotation period. Middle panel: phased light curve with the rotation period with the sinusoidal fit. Bottom panel: differential (V − I) color curve and the sinusoidal fit.