The v = 0, 1, 2, and 3, J = 1–0 SiO maser spectra of R Cassiopeia have been observed with high phase resolution over a time span of approximately 2.6 stellar periods. A time lag cross-correlation analysis has been performed on the entire data set and on two subsets of the data. The analysis indicates that the variations in the emission of the v = 1 and 2 states were most highly correlated at lag zero during the entire period of observation. During one complete cycle of the star, the v = 0, J = 1–0 emission was most highly correlated with the v = 1 and 2 at a lag of –1, indicating that the v = 0 emission varied in advance of the excited vibrational state emission. The lags represented 0.1 pulsation periods of the star, or a 43 day time period for these analyses. During a second cycle of the star the v = 0 and v = 2 emissions did not exhibit a maximum near the phase of 0.2 and were not highly correlated with the v = 1 emission. The lags represented 0.05 periods of the star for this analysis. The v = 0 emission generally had relatively low contrast between its maximum and minimum and had several relative maxima during a stellar period. The v = 3 emission was observed to occur at various phases of the star. These observations further constrain possible models of maser pumping.
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