Plot of the velocity half‐width in the central peak of the line profile vs. the ratio of the integrated intensity of the CO (2–1) line measured at the IRAM 30 m telescope compared with the flux at 60 μm measured by IRAS. In cases of complex line profiles (the Red Rectangle, BM Gem, X Her, and 89 Her), we take the velocity half‐widths for the prominent narrow component. The crosses represent data taken from all the carbon stars measured at IRAM by Olofsson et al. (1993) except for IRC+10216 which is nearby and the gas emission is highly resolved. The squares are data for oxygen‐rich semiregulars observed by Kahane & Jura (1994, 1996) while the triangles are from the data compiled by Loup et al. (1993), Kerschbaum & Olofsson (1998), or Groenewegen & de Jong (1998). The five circles in the lower left‐hand corner are denoted by RR = the Red Rectangle, AC = AC Her, 89 = 89 Her, BM = BM Gem, and EU = EU And. We denote the square for X Her by X.