SIO MASER SURVEY OF THE GALACTIC BULGE IRAS SOURCES .4. OBSERVATIONALPROPERTIES OF SIO MASERS

The statistical properties of SiO masers were studied based on observa tions of color-selected IRAS sources in the direction of the Galactic bulge. Among 313 observed late-type stellar objects in the region of \ l\ < 15 degrees and 3 degrees < \b\ < 10 degrees, 193 were detected in the SiO v = 1, J = 1 - 0 line and/or the v = 2, J = 1 - 0 line. We di scuss the relation between the SiO detection rate and the infrared pro perties for these sources. The sources were divided into bulge and dis k members in terms of the luminosity distance. The SiO detection rate was found to be appreciably higher for the bulge sources than for the disk sources, and the detection rate was found to be higher for variab le IRAS sources (with IRAS variability index above 90) than for the no nvariable sources (with an index below 90). We also found that the cen ter velocities of the v = 1 and v = 2, J = 1 - 0 lines are almost equa l to the average velocity of the OH 1612 MHz double peaks. This implie s that the SiO velocity is a good indicator of the stellar radial velo city, suggesting that an analysis of bulge stellar kinematics using Si O radial velocities is reasonable. On the average, the line-intensity ratio of the v = 1 to v = 2 lines is approximately unity, and there se ems to be no systematic difference in the ratio between disk and bulge sources. The SiO line intensities are very weakly correlated with the IRAS fluxes for bulge sources. No clear correlation has been found be tween the SiO line width and the stellar expansion velocity. This indi cates that the SiO line width cannot be used as a measure of the lumin osity of infrared sources.