Mapping the SiO masers in IRAS 16552-3050

Journal article, 2026

We report observations of SiO ( J = 1-0, v = 1 , and v = 2 ) maser emission at 43 GHz in IRAS 16552-3050 with the Nobeyama 45 m telescope and the Australia Telescope Compact Array. This is the second water fountain source known to harbor SiO masers. They are located within similar to 800 au of the dynamical center of the jet traced by H2O masers. The SiO masers present an elongated distribution in the north-south direction with the most blueshifted and redshifted components near the map center. While our absolute astrometric accuracy is modest (similar or equal to 0.''4), preventing a precise determination of the relative location of the SiO and H2O masers with respect to the central star, both are clearly associated with the same stellar source. Higher angular resolution observations are required to spatially resolve and more precisely locate the individual maser components. Nevertheless, the larger extent of the SiO maser distribution in IRAS 16552-3050 compared to that in W43A suggests that SiO masers in water fountains may exhibit a diversity of spatial distributions, similar to that observed in H2O masers. We argue that the properties of the H2O and SiO masers are consistent with several plausible scenarios, including a rotating torus, a shared outflow, a compact SiO-emitting region, and a fast bipolar outflow traced by H2O masers impacting a slowly expanding AGB shell. Further high-resolution observations are required to test these hypotheses.