A new interpretation of the feature of SiO maser spectra associated with M-type star

There exists a systematic redshift of spectra (nu =1,2; J=1-0) of SiO masers associated with a number of late-type M stars. On the contrary, the redshift is rather small for the spectra (nu =1; J=2-1). The latter is approximately symmetrical with respect to the star. For the above, no good interpretation has been given up to now. A new redshift mechanism of SiO spectra, the mechanism of radiation frequency shift, was derived here from the interaction between the radiation field of the star and the energy levels of the maser. Detailed calculations show that, under the influence of the radiation field of the star, the redshift of the SiO spectra (J=1-0) is more substantial than that of the spectra (J=2-1). This is consistent with the result of the observation, and shows that the nonkinematic effect of the spectra is non negligible for the SiO maser of the star.