Final Mass Loss on the AGB and Planetary Nebula Formation

New York University, New York NY

Investigators

Abstract

This project addresses an important unsolved problem in the evolution of ordinary (1 to 8 solar mass) stars in their transition from the asymptotic giant branch to the planetary nebulae phase: the nature of the final mass loss and the origin of their jets. Enhanced equatorial mass loss and high-velocity jets dominate the early development of planetary nebulae and appear to be nearly ubiquitous, but their origins are unknown. Here, observations of the neutral gas and dust ejected by the stars will be used to address key aspects of this evolutionary phase. 1) The Geometry of AGB Envelopes: Deep imaging will be carried out at optical wavelengths to determine the structure of circumstellar envelopes at the tip of the asymptotic giant branch. The results will be used to determine the long-term evolution of the mass loss geometry leading up to the transition, which provides key constraints on possible jet triggering mechanisms. 2) Jets and Equatorial Tori: Observations will also be made of newly formed jets and tori in proto/young planetary nebulae using ultra high resolution (roughly 0.3 arc sec) millimeter interferometry. Spectro-imaging of the molecular gas will be carried out in lines of 12CO, 13CO, and other molecular species to determine the geometry, mass, and dynamics of the jets and tori, and their inter-relations. The observations will be used to provide general constraints and to test specific scenarios of the final mass loss and jet formation. The results are expected to substantially improve our understanding of this key phase of stellar evolution. This project will impact other fields of astrophysics as planetary nebulae constitute a new class of objects with jets, whose distinct characteristics may offer novel insights on how jets can form. This project also involves the education and research training of graduate and undergraduate students at New York University. It further fosters international scientific co-operation, and forms the basis for Professor Huggins' on-going outreach efforts which are broadly centered on stellar evolution. This includes "Stars in the Curriculum," a collaborative program with an education specialist and practicing teachers, designed to enhance the science curriculum in public schools in New York City.