PLANETARY NEBULAE: THEIR EVOLUTION AND ROLE IN THE UNIVERSE IA U Symposium, Vol. 209, 2003 S. Kwok, M. Dopita, and R. Sutherland, eds. Interferometric Observations of OH and H 20 Masers in Protoplanetary Nebulae Imaged with HST -A Unique Diagnostic of their Spatio-Kinematic Structure Raghvendra Sahai JPL, California Institute of Technology, Pasadena, CA 91109 Mark J. Claussen NRAO, Socorro, NM 87801 Mark Morris University of California, Los Angeles, CA 90095 Recently, high-resolution imaging surveys of young planetary nebulae (PNe) and protoplanetary nebulae (PPNe) have revealed that the majority of these objects are characterised by multipolar bubbles distributed roughly point-symmetrically around the central star (e.g. Sahai & Trauger 1998, Sahai 2000). Sahai & Trauger (1998) have proposed that episodic high-speed jet-like outflows, oper- ating during the protoplanetary or very late-AGB phase, are the primary agent for shaping PNe. OH and H 2 0 masers provide a unique and crucial probe of the kinematics of the circumstellar material in PPNe, because of the general lack of other emission-line diagnostics. Here we present new results from our ongoing study of PPNe using HST images with interferometric OR & H 2 0 maser-line data to unravel their detailed spatio-kinematic structure (e.g. Sahai et al. 1999a, Sahai, Claussen, & Morris 2002). The "Water-Fountain Nebula", IRAS16342-3814 (hereafter IRAS1634), is a PPN belonging to a small class of unusual evolved stars with high velocity outflows traced in either or both of radio H 2 0 and OR maser line emission (e.g. Likkel & Morris 1988). The HST images of this PPN show a bipolar nebula - two bright lobes separated by a dark waist (Fig. 1 & Sahai et al. 1999b). The highest velocity OH features (",70 km s-l) are clustered around the base of the lobes and lower velocity features are found near the waist. We recently obtained VLBA observations of the H 2 0 emission, and find that it is concentrated in two blobs separated by 3".36 along the optical axis'", The blobs consist of numerous, closely spaced components, with radial velocities spanning 187 to 169km s-l in the red-shifted blob, and -62 to -69 km s-l in the blue one. Using the OR data, we lOthe orientation of the H20 maser axis is significantly different from that derived from VLA data (Sahai et al. 2002) taken 2 weeks prior to the VLBA run; we think that this is discrepancy is most likely due to some error(s) in the VLA data calibration for this rather low declination source 519 , available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0074180900209534 Downloaded from https://www.cambridge.org/core. IP address: 207.90.12.74, on 14 Jun 2019 at 01:44:27, subject to the Cambridge Core terms of use