ALMA observations of the water fountain pre-planetary nebula IRAS 16342-3814: high-velocity bipolar jets and an expanding torus

We have mapped CO J = 3-2 and other molecular lines from the >water fountain> bipolar pre-planetary nebula (PPN) IRAS 16342-3814 with ∼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 ( cm), 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 M yr in the past ∼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 (0.017 M ) of very large (∼millimeter-sized) grains. The measured expansion ages of the above structural components imply that the torus (age ∼160 years) and the younger high-velocity outflow (age ∼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.R.S.'s contribution to this research was carried out at JPL, California Institute of Technology, under a contract with NASA. W. V., C. S. C., and G. Q.-L. acknowledge support from ERC consolidator grant 614264, Spanish MINECO grant AYA2012-32032, and ERC Grant Agreement 610256 (NANOCOSMOS), respectively