PACS continuum subtracted spectra of our sample in the 55–75 μm range. The ¹²CO rotational lines are indicated by vertical dotted lines (see Table D.4). The upper-level rotational quantum number J_u of a few selected CO transitions are shown as a reference. The sources are sorted from top to bottom in these five groups: AGBs, S-type stars, extreme OH/IR stars, post-AGBs, and PNe. Within each category, targets are ordered based on the stellar effective temperature from the coolest source to the hottest one.