Fig. 4. CO (histogram plot) and SiO v =1 (thick continuous line) spectra for stars of Table 1 with R 0.7. The left and right Y-scales correspond to CO and SiO intensities respectively. For both lines the intensity scale is in main beam brightness temperature. Some stars are contaminated by galactic CO emission (TX Cam, VX Sgr, R Aql -mainly outside the line core-, OH104.9+2.4, and OH127.8-0.0); the corresponding channels have been omitted in the plots.