2007ApJ...657..482C

From the simultaneous observations of SiO v=3, J=2-1 and J=3-2 masers, SiO v=3, J=2-1 maser emission was detected for the first time toward the S-type Mira variable χ Cyg. The line was a single spike and was redshifted with respect to the stellar velocity. The SiO v=3, J=3-2 maser emission was not detected from this star. However, for the O-rich Mira variable TX Cam, SiO v=3, J=3-2 maser emission was detected, while v=3, J=2-1 maser was not detected. Two possible line overlaps were adopted as an explanation of these observational results.