Comparison between two ESPaDOnS spectra of o Lupi, taken two months apart (shown in gray), and synthetic ATLAS9/COSSAM_SIMPLE spectra. The red line is the synthetic spectrum for a single star with T_eff = 15 000 K, log g = 3.8 dex, and v sin i = 35 km s⁻¹, and the blue line is the synthetic spectrum for a binary star with T_eff, 1 = 17 000 K, T_eff, 2 = 14 000 K, log g₁ = 3.9 dex, log g₂ = 3.8 dex, v sin i₁ = 50 km s⁻¹, v sin i₂ = 25 km s⁻¹, RV₁ = −5 km s⁻¹, RV₂ = +5 km s⁻¹, and a light fraction of 50%. Residuals to the fit are indicated with the same color coding and a small offset for increased visibility. Top row: observed spectrum E01; bottom row: E02 (see also Table A.2).