Mg II k and Mg II UV 2 and 3 triplet lines profile. Vertical lines indicate particular wavelengths for which we determined different line parameters defined in Sect. 3 and listed in Table 2. The vertical blue line indicates the k line center and the two vertical red lines the k line peaks. The green are at ±1 Å from k line center. The vertical orange line is at 2800 Å. The vertical brown line and the two pink lines are centered, respectively, at the triplet Mg II UV center and the wings at 0.15 Å.