Sintering-induced Dust Ring Formation in HL Tauri's Protoplanetary Disk

Sintering-induced Dust Ring Formation in Protoplanetary Disks: Application to the HL Tau Disk

Authors:

Okuzumi et al

Abstract:

The latest observation of HL Tau by ALMA revealed spectacular concentric dust rings in its circumstellar disk. We attempt to explain the multiple ring structure as a consequence of aggregate sintering. Sintering is a process that reduces the sticking efficiency of dust aggregates, and takes place where the temperature is slightly below the sublimation point of some constituent material. We here present a dust growth model that incorporates sintering, and use it to simulate global dust evolution in a modeled HL Tau disk taking into account coagulation, fragmentation, and radial inward drift. We show that the aggregates collisionally disrupt and pile up at multiple locations where different volatiles cause sintering. At wavelengths of 0.87--1.3 mm, these "sintering zones" appear as bright, optically thick rings with spectral slope ≈ 2, whereas the non-sintering zones as darker, optically thinner rings of spectral slope ≈ 2.3--2.5, consistent with major bright and dark rings found in the HL Tau disk, respectively. Radial pileup and vertical settling occur simultaneously if disk turbulence is weak and if the monomers constituting the aggregates are ∼1 μm in radius. For the radial gas temperature profile of T=310(r/1 AU)−0.57 K, our model perfectly reproduces the brightness temperatures of the optically thick bright rings, and reproduces their orbital distances to an accuracy of ≲ 30%. The ring patterns diminish with time as dust is depleted from the disk, consistent with the idea that HL Tau is a young object.