1998AJ....116.2495C

We present the first detection of ³⁰SiO v=1, J=1-0 maser emission toward the Mira variable TX Cam among 18 surveyed evolved stars. The line width of this maser is much narrower than that of ³⁰SiO v=0, J=1-0 masers and the intensity is also weaker, indicating that it is unsaturated. The detection of the ³⁰SiO maser emission in the lowest rotational transition of the first vibrationally excited state, together with nearly simultaneous observations of the large number of ²⁹SiO and ²⁸SiO masers, provides good constraints for establishing the SiO maser pumping model of TX Cam. The global features of ³⁰SiO and ²⁹SiO v=1, J=1-0 lines are similar, but detailed characteristics, such as their half-widths, their peak intensity ratios of the v = 1, J = 1-0 line to the v = 0, J = 1-0 line, and their intensity variation with time, are different. New detection of the ³⁰SiO v=0, J=1-0 and J=2-1 lines is also reported in six evolved stars: TX Cam, R Cas, χ Cyg, W Hya, U Lyn, and WX Psc. They show a different masing characteristics of the ³⁰SiO that depends on both sources and transitions. This is probably related to a critical condition for masing.