A Young Protoplanet Candidate Embedded in the Circumstellar Disk of HD 100546

We present high-contrast observations of the circumstellar environment of the Herbig Ae/Be star HD 100546. The final 3.8 μm image reveals an emission source at a projected separation of 0.''48 ± 0.''04 (corresponding to ~47 ± 4 AU) at a position angle of 8.°9 ± 0.°9. The emission appears slightly extended with a point source component with an apparent magnitude of 13.2 ± 0.4 mag. The position of the source coincides with a local deficit in polarization fraction in near-infrared polarimetric imaging data, which probes the surface of the well-studied circumstellar disk of HD 100546. This suggests a possible physical link between the emission source and the disk. Assuming a disk inclination of ~47°, the de-projected separation of the object is ~68 AU. Assessing the likelihood of various scenarios, we favor an interpretation of the available high-contrast data with a planet in the process of forming. Follow-up observations in the coming years can easily distinguish between the different possible scenarios empirically. If confirmed, HD 100546 "b" would be a unique laboratory to study the formation process of a new planetary system, with one giant planet currently forming in the disk and a second planet possibly orbiting in the disk gap at smaller separations.

Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, under program number 087.C-0701(A).