Cloudlet capture model for the accretion streamer onto the disc of DG Tau

Abstract

ABSTRACT DG Tau is a nearby T Tauri star associated with a collimated jet, a circumstellar disc, and a streamer a few hundred au long. The streamer connects to the disc at ∼50 au from DG Tau. At this location SO emission is observed, likely due to the release of sulphur from dust grains caused by the shock of the impact of the accretion streamer onto the disc. We investigate the possibility that the DG Tau streamer was produced via cloudlet capture on the basis of hydrodynamic simulations, considering a cloudlet initiating infall at 600 au from DG Tau with low angular momentum so that the centrifugal force is smaller than the gravitational force, even at 50 au. The elongation of the cloudlet into a streamer is caused by the tidal force when its initial velocity is much less than the free-fall velocity. The elongated cloudlet reaches the disc and forms a high-density gas clump. Our hydrodynamic model reproduces the morphology and line-of-sight velocity of CS (5 − 4) emission from the northern streamer observed with Atacama Large Millimeter/submillimeter Array. We discuss the conditions for forming a streamer based on the simulations. We also show that the streamer should perturb the disc after impact for several thousands of years.