A Resolved Circumstellar Disk around the Herbig Ae Star HD 100546 in the Thermal Infrared

We present mid-infrared nulling interferometric and direct imagingobservations of the Herbig Ae star HD 100546 obtained with the Magellan I(Baade) 6.5 m telescope. The observations show resolved circumstellar emissionat 10.3, 11.7, 12.5, 18.0, and 24.5 microns. Through the nulling observations(10.3, 11.7 and 12.5 microns), we detect a circumstellar disk, with aninclination of 45 +- 15 degrees with respect to a face-on disk, a semimajoraxis position angle of 150 +- 10 degrees (E of N), and a spatial extent ofabout 25 AU. The direct images (18.0 and 24.5 microns) show evidence for coolerdust with a spatial extent of 30-40 AU from the star. The direct images alsoshow evidence for an inclined disk with a similar position angle as the diskdetected by nulling. This morphology is consistent with models in which aflared circumstellar disk dominates the emission. However, the similarity inrelative disk size we derive for different wavelengths suggests that the diskmay have a large inner gap, possibly cleared out by the formation of a giantprotoplanet. The existence of a protoplanet in the system also provides anatural explanation for the observed difference between HD 100546 and otherHerbig Ae stars.Comment: 13 pages, 2 figures, Accepted for publication in ApJ Letter