The P(8) ¹²CO line is plotted for the entire sample broad-based single peaked sources, apart from VW Cha for which the P(10) line is presented because the P(8) line is affected by a strong telluric feature at the time of observation. The lines have been continuum subtracted and normalized. The asymmetry of the VV CrA A line is caused by line blending by the CO v = 3–2 R(5) line. This line overlap adds intensity on the blue side of the ¹²CO P(8) line.