High-Excitation 29SiO and 30SiO Maser Emission

We present the first detection of strong maser emission from high-J rotational levels of the v = 1, 2 vibrationally excited states of (Si-30)O and (Si-29)O in the oxygen-rich supergiant star VY CMa. In addition, both isotopes present strong maser emission in the J = 5-4 line of the ground vibrational state (v = 0). The obtained results, in particular the strong variations in intensity and profile of the different rotational lines within a given vibrational state, favor the interpretation of these masers as due to thermal and/or nonlocal overlap of the infrared lines of (Si-28)O with those of (Si-29)O and (Si-30)O, a mechanism that has been proposed by Cernicharo, Bujarrabal, and Lucas (1991) to pump the J = 4-3 v = 1 maser line of (Si-29)O.