The lifetime of mira's SiO maser features

Maser spectra of the long period variable star Mira have been observed for approximately four stellar periods in the silicon monoxide (SiO) v = 1, J = 1 - 0 transition using the 37 m Haystack Radio Telescope. The linear polarization characteristics of the spectra have been determined. The lifetimes and beginning and ending phases of 15 maser features have also been extracted from Gaussian fits to the polarized spectra. Previously it had been suggested that features disappear at or near phase 0, the optical maximum. Recently it has been proposed that the maser emissions of long period variables are affected by the passage of a shock wave through the circumstellar region in which the masers originate. The proposed shock passage produces a fading of the emission by phase 0.4. The results of the Gaussian fits indicate that 10 of 15 features came into existence between phases 0.8 and 0.1 and 7 went out of existence between phases 0.3 and 0.4. One feature had a lifetime greater than the period of the star.