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

Abstract

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 mm. Through the nulling observations (10.3, 11.7, and 12.5 mm), we detect a circumstellar disk, with an inclination of with respect to a face-on disk, a semimajor axis 45 15 position angle of (east of north), and a spatial extent of about 25 AU. The direct images (18.0 and 150 10 24.5 mm) 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.