SIMULTANEOUS OBSERVATIONS OF SiO AND H sub(2)O MASERS TOWARD KNOWN STELLAR SiO MASER SOURCES

We carried out simultaneous observations of four maser lines, SiO v = 1, 2, super(29)SiO v = 0, J = 1-0, and H sub(2)O 6 sub(16)-5 sub(23), toward 83 known SiO maser sources without H sub(2)O maser detections using the Korean VLBI Network single dish telescopes. Both SiO and H sub(2)O masers were detected from 14 sources, resulting in a detection rate of 16.9%. H sub(2)O maser emission without SiO maser emission was detected from one source. Therefore, H sub(2)O maser emission was newly detected from 15 sources. SiO maser emission without H sub(2)O detection was detected from 55 sources, which gives a total SiO maser detection rate of 83.1% when including sources that have both SiO and H sub(2)O maser emission detected. SiO v = 2 maser emission was detected from nine sources without v = 1 maser detection. The SiO v = 2 maser sources without the v = 1 maser detections need to be investigated, with a large number of v = 2 only maser sources related to the development of dust shells and their evolutionary sequence from asymptotic giant branch (AGB) to post-AGB stars. The average values of the peak and integrated antenna temperature ratios of H sub(2)O to SiO masers are 0.44 and 0.28 in the 14 sources that have both SiO and H sub(2)O detections. Observational characteristics of several individual sources are noted and the dependence of the different maser intensity ratios on the stellar phase is discussed. In addition, the observational results of SiO and H sub(2)O masers are discussed in IRAS two-color diagrams.