Sequential planet formation in the HD 100546 protoplanetary disk?

Context. The disk around the Herbig Ae star, HD 100546, shows structures that suggest the presence of two companions in the disk at similar to 10 and similar to 70 AU. The outer companion seems to be in the act of formation. Aims. Our aims are to provide constraints on the age of the planets in HD 100546 and to explore the potential evidence for sequential planet formation in transition disks such as HD 100546. Methods. We compare the recent resolved continuum observations of the disk around HD 100546 with the results of dust evolution simulations using an analytical prescription for the shapes of gaps carved by massive planets. Results. An inner pressure bump must have been present since early in the disk lifetime to have good agreement between the dust evolution models and the continuum observations of HD 100546. This pressure bump may have resulted from the presence of a very massive planet (similar to 20 M-Jup), which formed early in the inner disk (r similar to 10 AU). If only this single planet exists, the disk is likely to be old, comparable to the stellar age (similar to 5-10 Myr). Another possible explanation is an additional massive planet in the outer disk (r similar to 70 AU): either a low- mass outer planet (less than or similar to 5 M-Jup) injected at early times, or a higher mass outer planet (greater than or similar to 15 M-Jup) formed very recently, traps the right amount of dust in pressure bumps to reproduce the observations. In the latter case, the disk could be much younger (similar to 3.0 Myr). Conclusions. In the case in which two massive companions are embedded in the disk around HD 100546, as suggested in the literature, the outer companion could be at least greater than or similar to 2.5 Myr younger than the inner companion.