The Progression of Mass-Loss During the AGB Star?Planetary Nebula Transition

Details The Progression of Mass-Loss During the AGB Star?Planetary Nebula Transition The Progression of Mass-Loss During the AGB Star?Planetary Nebula Transition

Sep 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004sptz.prop.3668m&link_type=abstract

Spitzer Proposal ID #3668

Computer Science

Scientific paper

Mass loss on the asymptotic giant branch is a short-lived (few x 10^5 years) process that dramatically transforms low and intermediate-mass stars into white dwarfs, producing planetary nebulae during the transition. Evidence from molecular line observations, from optical studies of ionized gas, and from previous far-infrared studies from space collectively tends to indicate that the mass-loss process is unsteady, sometimes leading to one or more outflowing shells of matter, separated by distances that correspond to time scales of a few tens of thousands of years. However, because of the spherical divergence of the outflowing matter, it has been difficult to follow it in individual objects out to large enough radial distances that a large portion of the mass-loss history can be traced. We propose a pilot program with the MIPS imager on Spitzer to observe the extended dusty envelopes of six stars out to angular distances as large as 10 - 20 arcminutes, typically more than a parsec. At the usual speeds of AGB winds, ~15 km/s, such angular scales correspond to envelope expansion times approaching 10^5 years. Taking advantage of the sensitivity of MIPS to the faint outer emission from these outflows, we will be able to characterize the time variation in mass loss rate for this group of stars better than has previously been possible in any star. Once the time scales and the regularity, or lack thereof, of the shell ejection process have been established, these results can be used to constrain models for thermal pulsing in AGB stars, including how the interpulse period and pulse duration vary with the diminution of the stellar mass caused by mass loss. Our results will also provide a view of the asymmetric magnetohydrodynamic interaction between the outflowing wind and the ambient interstellar medium for comparison with recent models.

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