The Mg i 517.268 nm line for HE 1148–0037, in spectra taken at JD 2 453 787.6803 (black continuous line) and JD 2 453 823.5443 (red dashed line), separated by 35.86 days. The spectra have been normalized, and Doppler shifted to bring the primary component to a rest-frame wavelength. The binarity is readily visible, as well as the variation in the components’ separation.