Detection plots for star W57. Top: SSF in the q − T_eff plane. The vertical green line marks the lower limit of q according to the spectroscopic mass function and an estimated primary mass of 1.4 M_⊙. The yellow line shows the temperature for each possible value of the secondary mass, assuming it is a main-sequence star of the age of the cluster. Bottom: Cross-correlation function of the reconstructed secondary spectrum for several experiments adding artificial secondaries to the observed spectra. The inset shows the contribution of the secondary star to the total flux.