Streamers feeding the SVS13-A protobinary system: astrochemistry reveals accretion shocks?

Abstract

We report Atacama Large Millimeter/submillimeter Array (ALMA) high-angular resolution (∼50 au) observations of the binary system SVS13-A. More specifically, we analyse deuterated water (HDO) and sulfur dioxide (SO₂) emission. The molecular emission is associated with both the components of the binary system, VLA4A and VLA4B. The spatial distribution is compared to that of formamide (NH₂CHO), previously analysed in the system. Deuterated water shows an additional emitting component spatially coincident with the dust-accretion streamer, at a distance ≥120 au from the protostars, and at blue-shifted velocities (>3 km s⁻¹ from the systemic velocities). We investigate the origin of the molecular emission in the streamer, in light of thermal sublimation temperatures calculated using updated binding energy (BE) distributions. We propose that the observed emission is produced by an accretion shock at the interface between the accretion streamer and the disk of VLA4A. Thermal desorption is not completely excluded in case the source is actively experiencing an accretion burst.