Location and phase of dust formation in IRC + 10216 indicated by 11 micron spatial interferometry

A new long-baseline interferometer for the 10-micron region has provided visibility measurements of IRC + 10216 at spatial frequencies in the range 1.4-12 x 10 to the 5th/rad. These show large changes in visibility with phase of the LPV's luminosity. Model fitting of the visibility curves indicates that dust forms closer to the star and at higher temperatures than has been indicated by previous measurements. In addition, new dust appears to form near minimum luminosity. There is general agreement with previous theoretical expectation that dust should form at temperatures above about 1300 K and that close to the star the material is less transparent at mid-IR wavelengths than in the near-IR.