Astronomy Tea Talk
Planet formation by dust coagulation in protoplanetary disks is one of the long standing problems in disk evolution theory. Dust grains must grow from submicron sizes to ~10 MEarth rocky cores within the ~10 Myr lifetime of the circumstellar disk. However, this growth process is hindered by collisional fragmentation and rapid inward radial drift. A possible solution in dust evolution theory is dust trapping in local pressure maxima in the disk, where dust particles pile up and grow. Transitional disks with large inner dust cavities have been suggested to contain these dust traps. I present the first results of our ALMA Cycle 0 program using Band 9, imaging the Herbig Ae star Oph IRS 48 in CO(6-5), C17O(6-5) and the submillimeter continuum in the extended configuration. The resulting 0.2'' spatial resolution completely resolves the cavity of this disk in the gas and the dust. The gas cavity of IRS 48 is only half as large as the dust cavity and the gas surface density inside this gas cavity is at least two orders of magnitude lower than the gas in the surrounding ring. The micrometer-sized dust grains follow a large ring-like structure as well. On the other hand, the continuum emission, tracing the millimeter-sized dust, reveals an unexpected huge asymmetry and steep edges in the dust distribution along the ring. The difference in distribution of big grains versus small grains/gas can be modeled with a vortex-shaped dust trap triggered by a companion. I will discuss the implications for the dust trapping scenario in transitional disks, compare IRS 48 with other ALMA Cycle 0 results and discuss future possibilities with ALMA.