An analytical model of the SiO maser velocity spectrum

SiO maser sources associated with Mira variables show a wide velocity spread in the spectral line and a variety of profiles. We think this velocity spread may be ultimately traced to the star's pulsation. We consider the propagation of a perturbation generated by the pulsation in the circumstellar envelope, regarded as a compressible fluid. Using observed average parameter values for the Mira stars, our model gives, at the distance of the SiO maser, a velocity spread of ±6 km/s, in good agreement with the observed widths. The question of a correlated variation of the line width with the optical phase is also discussed