2006ApJ...653.1353M

We present high-sensitivity subarcsecond resolution images of the Herbig Ae star AB Aurigae at 11.6 and 18.5 µm taken with Michelle on Gemini North. Bright extended dust emission close to the star is resolved at both wavelengths, with a quadratically subtracted FWHM of 17±4 AU at 11.6 µm and 22±5 AU at 18.5 µm. Additional fainter emission is detected out to a radius of 280 AU at 11.6 µm and 350 AU at 18.5 µm down to the sensitivity limit of the observations. The latter value is identical to the measured size of the millimeter-continuum disk, but much smaller than the CO disk. Assuming moderately absorbing material, we find that larger particles (∼1 µm) dominate the mid-IR emission in the inner (<100 AU) regions of the disk, and smaller particles (<0.3 µm) dominate in the outer regions of the disk. A model of a nearly face-on passive flared disk with an inner rim accounts well for our observations.