Bandpasses of HFI with the location of bright CO rotational lines (J = 1 → 0, 2 → 1, 3 → 2, 4 → 3, and 5 → 4 from left to right) shown as a horizontal black line with tick marks. The CO lines can introduce a significant positive bias in the flux density of the sources, particularly those associated with Galactic star-forming regions. The effect is the most significant at 100GHz where the flux density may be boosted by more than 50%. See Planck HFI Core Team (2011b) for details.