Upper panel: scargle periodogram of the radial velocities of SDSS J0039 measured using a double Gaussian with widths 300 km s^-1 and separation 2000 km s^-1. The measured period and uncertainty from the first night’s observations alone are indicated with a thick line. Lower panel: measured radial velocities (filled circles) compared to the best-fitting spectroscopic orbit (unbroken line). The errorbars include only the Poisson noise contribution to the velocity measurements.