IRAS two-color diagram of observational results for the P.F values of SiO21 and SiO11 masers according to the SRs, Miras, and OH/IR stars. Sources with a higher P.F value for SiO11 than SiO21 are marked in green, while those with a higher P.F value for SiO21 are marked in red. SiO21-only sources are identified in black with numbers (V Leo (#47) and OH43.8+0.5 (#112)). The curved and blue dashed lines represent the same as in Figure 8.