Radial velocity curves for both components in WR 21a from the orbital solution of Tramper et al. (2016). The dashed blue and continuous red lines provide the curves for the secondary and primary, respectively. The dots represent the RVs measured on the 2013 FEROS spectra acquired contemporaneously with the XMM-Newton data. The agreement with the pre-established orbital solution is good. The error-bars represent 1σ standard deviation.