A resolved circumstellar disk around the Herbig Ae star HD 100546 in the thermal infrared

We present mid-infrared nulling interferometric and direct imaging observations of the Herbig Ae star HD 100546 obtained with the Magellan I (Baade) 6.5 m telescope. The observations show resolved circumstellar emission at 10.3, 11.7, 12.5, 18.0, and 24.5 μm. Through the nulling observations (10.3, 11.7, and 12.5 μm), we detect a circumstellar disk, with an inclination of 45° ± 15° with respect to a face-on disk, a semimajor axis position angle of 150° ± 10° (east of north), and a spatial extent of about 25 AU. The direct images (18.0 and 24.5 μm) show evidence for cooler dust with a spatial extent of 30-40 AU from the star. The direct images also show evidence for an inclined disk with a similar position angle as the disk detected by nulling. This morphology is consistent with models in which a flared circumstellar disk dominates the emission. However, the similarity in relative disk size that we derive for different wavelengths suggests that the disk may have a large inner gap, possibly cleared out by the formation of a giant protoplanet. The existence of a protoplanet in the system also provides a natural explanation for the observed difference between HD 100546 and other Herbig Ae stars.