AAS 207th Meeting, 8-12 January 2006
Session 86 Ground Based Optical Interferometry
Special Session, Tuesday, 10:00-11:30am, January 10, 2006, Delaware A

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[86.03] Circumstellar Environments of Evolved Stars

J. D. Monnier (U. Michigan)

Infrared interferometers can now directly view the photospheric structure and the circumstellar environments of AGB stars on sub-AU scales. This talk will summarize major progress that has been achieved in two different areas. Firstly, interferometers have discovered a new warm water vapor layer around AGB stars, which has been difficult or impossible to study using spectra alone. In fact, this work can explain a number of mysteries, most notably the "large" stellar diameters measured by 10 micron interferometry. In addition, closure phase data has now shown that AGB stars often have significant asymmetries on their surface -- but from what? Secondly, hot, newly-formed dust shells have been imaged by combining single-aperture diffraction-limited imaging with long-baseline interferometry. These results show large asymmetries in the dust distribution and challenge some basic assumptions of mass-loss theory -- could clumpy dust production be related to the surface irregularities also being observed? Major progress is expected soon across the infrared when spectroscopy and interferometry are combined at new facilities.

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