1998A&A...329..219P

We present simultaneous observations of several rotational lines of ²⁸SiO in the v=1, 2, 3, and 4 vibrationally excited states toward O-rich evolved stars. All the data were taken in a relatively short period of 65 days, which allows a comparative study of the ²⁸SiO maser lines intensities and profiles. The observed differences concerning intensity and line shape among the different maser lines suggest that infrared overlaps deeply affect the pumping of some SiO masers. We qualitatively discuss this effect with consideration to the IR overlaps at 8 µm between the various SiO isotopomers and between ²⁸SiO and water vapor