Abstract
We report on the first detection of maser emission in the J = 11-10, J = 14-13, and J = 15-14 transitions of the v = 0 vibrational state of SiS toward the carbon-rich star IRC +10216. These masers seem to be produced in the very inhomogeneous region between the star and the inner dust formation zone, located at ≃(5-7)R*, with expansion velocities below 10 km s-1. We interpret the pumping mechanism as being due to overlaps between v = 1-0 rovibrational lines of SiS and mid-IR lines of C2H2, HCN, and their 13C isotopologues. The large number of overlaps found suggest the existence of strong masers for high-J v = 0 and v = 1 SiS transitions, located in the submillimeter range. In addition, it could be possible to find several rotational lines of the SiS isotopologues displaying maser emission.
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