Subtraction of C₂ lines from the spectra of comets C/2002 T7 (LINEAR), 8P/Tuttle and 103P/Hartley 2. The black spectrum shows the data not corrected for C₂ while in the green one is after removing the C₂ lines contamination. The C₂ synthetic spectrum is represented by the dotted red line. The positions of C₂ lines at 5577.331 Å, 5577.401 Å and 5577.541 Å are indicated with small vertical thick marks. The telluric [OI] line (⊕) is visible in the spectrum of comet 103P/Hartley 2.