ALMA Observations of the Water Fountain Pre-planetary Nebula IRAS 16342-3814: High-velocity Bipolar Jets and an Expanding Torus

R. Sahai, W.H.T. Vlemmings, T. Gledhill, C. Sanchez Contreras, E. Lagadec, L-A. Nyman, G. Quintana-Lacaci. 2017. ALMA Observations of the Water Fountain Pre-planetary Nebula IRAS 16342-3814: High-velocity Bipolar Jets and an Expanding Torus. Astrophysical Journal Letters 835, 1, DOI: 10.3847/2041-8213/835/1/L13

We have mapped (CO)-C-12 J = 3-2 and other molecular lines from the «water fountain» bipolar pre-planetary nebula (PPN) IRAS 16342-3814 with similar to 0 ». 35 resolution using Atacama Large Millimeter/submillimeter Array. We find (i) two very high-speed knotty, jet-like molecular outflows; (ii) a central high-density (> few x 10(6) cm(-3)), expanding torus of diameter 1300 au; and (iii) the circumstellar envelope of the progenitor AGB, generated by a sudden, very large increase in the mass-loss rate to > 3.5 x 10(-4) Me-circle dot yr(-1) in the past similar to 455 years. Strong continuum emission at 0.89 mm from a central source (690 mJy), if due to thermally emitting dust, implies a substantial mass (0.017M(circle dot)) of very large (similar to millimeter-sized) grains. The measured expansion ages of the above structural components imply that the torus (age similar to 160 years) and the younger high-velocity outflow (age similar to 110 years) were formed soon after the sharp increase in the AGB mass-loss rate. Assuming a binary model for the jets in IRAS 16342, the high momentum rate for the dominant jet-outflow in IRAS 16342 implies a high minimum accretion rate, ruling out standard Bondi-Hoyle-Lyttleton wind accretion and wind Roche-lobe overflow (RLOF) models with white-dwarf or main-sequence companions. Most likely, enhanced RLOF from the primary or accretion modes operating within common-envelope evolution are needed.

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