AAS 201st Meeting, January, 2003
Session 89. Planetary Nebulae and Dusty Clouds
Poster, Wednesday, January 8, 2003, 9:20am-6:30pm, Exhibit Hall AB

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[89.12] The Youngest Pre-Planetary Nebulae: An Interferometric Snapshot Survey of CO J=1-0 emission

C. Sanchez Contreras (Caltech), R. Sahai (Caltech/JP)

The transition between the Asymptotic Giant Branch (AGB) to the Planetary Nebula (PN) stage through the intermediate evolutionary stage of Pre-Planetary Nebula (PPN) is characterized by dramatic changes in the morphology and kinematics of the circumstellar envelopes associated with these objects. At some point in the late AGB stage a process (or processes) becomes operative that accelerates and imposes bipolarity upon the slow, spherical AGB winds. What produces bipolarity in these objects and at what stage of evolution does bipolarity manifest itself are key questions of post-AGB evolution that remain yet poorly understood.

We are carrying out a multi-wavelength imaging/spectroscopic survey searching for bipolarity (and other systematic departures from sphericity) and fast outflows in OH/IR stars, which are the immediate predecessors of PPNe (i.e. the youngest PPNe). Our main goal is to probe, in their infancy, the physical processes that produce asphericity. This ongoing survey includes optical imaging/spectroscopy of a large sample of candidate young PPNe, selected from catalogs of OH/IR stars (see R. Sahai & C. Sánchez Contreras in this session) and CO J=1-0 emission interferometric observations (using the OVRO Millimeter Array) of our best PPNe candidates (i.e. objects with aspherical morphology in the optical and/or intense, broad H\alpha emission). Here we report the first results from our CO emission mapping survey. These data probe cool, dense molecular gas, which comprises the most massive component of these objects. CO emission data are crucial for estimating several important physical parameters, such as the systemic velocity (useful for deriving the source distance using a Galactic rotation model), the terminal velocities of the slow and fast winds (when present), the mass-loss rates, and the total circumstellar mass and linear momentum, which are needed to get a better understanding of post-AGB evolution.

This work is partially funded through a NSF grant (No. 9981546) to OVRO and NASA LTSA grant (No. 399-30-61-00-00) to R.S.

The author(s) of this abstract have provided an email address for comments about the abstract: sanchez@astro.caltech.edu

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