Mid-infrared interferometry on spectral lines: II. Continuum (dust) emission around IRC +10216 and VY CMa

The U. C. Berkeley Infrared Spatial Interferometer has measured the mid-infrared visibilities of the carbon star IRC +10216 and the red supergiant VY CMa. The dust shells around these sources have been previously shown to be time-variable, and these new data are used to probe the evolution of the dust shells on a decade time-scale, complementing contemporaneous studies at other wavelengths. Self-consistent, sphericallysymmetric models at maximum and minimum light both show the inner radius of the IRC +10216 dust shell to be much larger (150 mas) than that expected from the dust condensation temperature, implying that dust production has slowed or stopped in recent years. Apparently, dust does not form every pulsational cycle (638 days), and these mid-infrared results are consistent with recent near-IR imaging which indicates little or no new dust production in the last three years (Tuthill et al. 2000). Spherically symmetric models failed to fit recent VY CMa data, implying that emission from the inner dust shell is highly asymmetric and/or time-variable. Subject headings: instrumentation: interferometers, techniques: interferometric, stars: AGB and post-AGB, stars: circumstellar matter, stars: winds Current Address: Smithsonian Astrophysical Observatory MS#42, 60 Garden Street, Cambridge, MA, 02138 Current Address: NASA Goddard Space Flight Center, Infrared Astrophysics, Code 685, Greenbelt, MD 20771 Current Address: Laboratory of Chemical Physics, Building 5, Room 114, National Institutes of Health, Bethesda, MD, 20892-0520 Current Address: Chatterton Astronomy Dept, School of Physics, University of Sydney, NSW 2006, Australia