Detection map of the NACO observations of CHXR 74. Displayed are the parameter space of detectable companions in terms of K-band brightness ratio and binary separation. The black curve denotes the detection limit for a S/N of 5. The blue vertical line represents the minimum binary separation (18 mas) at the time of the NACO observations and the red horizontal line the model-dependent lower limit of the K-band brightness ratio, both derived from the RV orbit. See text for more details.