Profiles of the 4428 Å feature in Tc 1 (left panel) and in the comparison star HR 6334 (right panel) superposed on the profile of the O6.5 star HD 148937. The O6.5 star has been displaced (in velocity) in both panels to make the 4428 Å band coincide with the profile and the minima of the 4428 Å band towards Tc 1 and HR 6334. All spectra have been normalized on the EQW of the 4428 Å band. The minimum of the feature in HR 6334 occurs around 0.0 km s^-1, while it seems to be blue-shifted in Tc 1. The green profiles of the 4428 Å feature in Tc 1 and HR 6334 are the polynomial fits shown in Fig. 6. The superposed spectrum of an O6.5 star (in blue) support the non-coincidence of the profiles minima in Tc 1 and HR 6334.