Excavating the Mass Loss History in the Circumstellar Dust Shells of Evolved Stars (Spitzer-MLHES)

Details Excavating the Mass Loss History in the Circumstellar Dust Shells of Evolved Stars (Spitzer-MLHES) Excavating the Mass Loss History in the Circumstellar Dust Shells of Evolved Stars (Spitzer-MLHES)

May 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007sptz.prop40092u&link_type=abstract

Spitzer Proposal ID #40092

Computer Science

Sound

Scientific paper

Using Spitzer/MIPS's unique observing capabilities, we propose to observe the spatial distribution of the far-IR emission from extended circumstellar dust shells (CDSs) of 37 asymptotic giant branch (AGB) stars. Our sample is volume-limited (< 500 pc) and includes all known extended AGB CDSs whose internal structures can be resolved by Spitzer at 70 microns. We will determine the dust distribution in these shells and thus, (a) directly characterize AGB mass loss variations in the CDSs; (b) confront our observational data with a range of theoretical predictions to determine the effect of dust chemistry on mass loss and the cause of the aspherical CDS structures; and (c) constrain the masses of the progenitor stars. Most importantly, we will achieve our science goals by deriving statistically sound conclusions using a complete structure-resolvable sample in the solar neighborhood. The mechanisms by which these evolved stars lose their mass to the surrounding space are not well understood. The AGB CDSs contain the fossil record of their mass loss, and therefore have the potential to verify many aspects of stellar evolution. IRAS and ISO data indicate that extended AGB CDSs exist showing evidence for mass-loss variations that correlate with evolutionary changes in the star itself. However, previous observations lacked both quantity (data are scarce) and quality (sensitivity and spatial resolution) to investigate the full extent and detailed structure of these large CDSs in statistically meaningful ways. Hence, it is more than timely to apply the powerful capabilities of Spitzer/MIPS to study the far-IR structure and evolution of these extended CDSs at moderately high resolution and sensitivity, for which there are presently no superior alternatives to Spitzer. The AGB CDSs are being detected at a high rate (> 60%) in an on-going AKARI-MLHES study at lower resolution and sensitivity: the likelihood for success of this proposed Spitzer-MLHES program at higher resolution and sensitivity is therefore enhanced.

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