9521605 Meixner Mass loss has a profound effect on the final evolution of intermediate mass stars. Unfortunately, the physical mechanism driving the extreme mass loss rates on the asymptotic giant branch (AGB) is not understood. Dr. Margaret Meixner of the University of Illinois, Urbana-Champaign, will conduct an observational investigation of the nature of the mass loss in evolved stars using imaging techniques in two wavebands: millimeter wavelength (3 mm), and mid-IR wavelength (8-25 microns). The carbon monoxide emission millimeter wavelength (transition J=1-0) imaging project utilizes the Berkeley-Illinois-Maryland millimeter wavelength array (BIMA) and the NRAO 12m telescope for observations, and a detailed radiative transfer software code for the analysis of the data. The expected results will include more accurate determination of mass loss rates and characterization of the large scale halos (radii about 70 arc seconds) which are found in all evolved stars; and compact (less than 4 arc seconds) fast molecular gas regions, which are found in transition objects such as proto-planetary nebulae (PPNe) and hold a clue to the AGB to planetary nebula (Pne) transition process. The mid-IR wavelength imaging project involves the analysis of high resolution (less than 1 arc second) mid-IR wavelength images of 55 circumstellar dust shells (CDSs) surrounding AGB stars, PPNe and young Pne, will be carried out using an axially symmetric radiative transfer dust code. Moreover, the mid-IR wavelength project includes further observations of PPNe and extreme AGB stars at similar and longer wavelengths and at high angular resolutions (about 0.1 arc seconds) using two mid-IR wavelength array cameras (MIRAC and the Keck LWIRC). The results from this mid-IR wavelength imaging project will provide insight into the origin of axially symmetric morphological structures commonly found in Pne and insight into the evolutionary stage at which this axial symmetry arises. Dr. Me ixner has three activities planned that will lay ground work for the future research. Firstly, an observing run is planned with the MIRAC team in June 1995 to observe approximately one dozen PPNe. Secondly, a new axially symmetric computer software dust code will be used to model several mid-IR images of PPNe and Pne from the current sample; thereby demonstrating the application of this code. Finally, carbon monoxide wavelength emission data cubes of three objects will be constructed using a new interferometry technique called mosaicing; thereby demonstrating the feasibility of this technique.
