Mid-infrared observations of disks

Mid-IR (5-30 mum) observations of circumstellar disks sample dust located within a few hundred AU of the stars, a region that is particularly relevant to the birth and evolution of planetary systems. While planets themselves are currently too faint to detect directly, a planet can perturb a disk, altering its structure in a way that may be detectable by high-angular-resolution mid-IR imaging. With the largest ground-based telescopes, the angular resolution at these wavelengths is typically 0."3, which for a star at 20 pc, corresponds to 6 AU. One can therefore probe structures comparable in size to potential planetary orbits. Multi-wavelength mid-IR imaging also provides a realistic basis for estimating the dust temperature, emission efficiency, and number density as a function of position within disks. Among other things, this information bears on the particle size distribution and, consequently, on the dynamical behavior of the disk particles in response to radiation pressure and other forces. In this review, I describe the role that mid-IR astronomy can play in the exploration of circumstellar disks and I present an assessment of some of the most recent mid-IR imaging of disks and their environments. I emphasis Vega-type disks and their (presumed) progenitors, the Herbig Ae/Be stars. Finally, I touch on the capabilities that the newest generation of large ground-based telescopes will provide for exploration of disks in the mid-IR.