Accretion vs. Core-Filament Collision: Implications for Streamer Formation in Per-emb-2

TL;DR

This study investigates the origin of a large streamer around protostar Per-emb-2, concluding it results from a core-filament collision rather than accretion, based on molecular line observations and velocity analysis.

Contribution

It introduces the core-filament collision scenario as the formation mechanism for the streamer, contrasting with the traditional accretion model.

Findings

The streamer is unlikely to be connected to the bridge, indicating no accretion origin.

The collision fragmented the filament, forming the streamer and a shock remnant.

The streamer does not significantly contribute to protostellar mass growth.

Abstract

Recent millimeter and submillimeter observations have unveiled elongated and asymmetric structures around protostars. These structures, referred to as streamers, often exhibit coherent velocity gradients, seemingly indicating a directed gas flow towards the protostars. However, their origin and role in star formation remain uncertain. A protostellar core Per-emb-2, located in Barnard 1, has a relatively large streamer with $10^4$ au, which is more prominent in emission from carbon chain molecules. We aim to unveil the formation mechanism of this streamer. We conducted mapping observations towards Per-emb-2 using the NRO 45-m telescope. We targeted carbon chain molecular lines such as CCS, HC$_3$N, and HC$_5$N. Using astrodendro, we identified one protostellar and four starless cores, including three new detections, on the Herschel map. The starless and protostellar cores are more or less gravitationally bound. We discovered strong CCS and HC$_3$N emissions extending from the north to the south, appearing to bridge the gap between the protostellar core and the starless core north of it. This bridge spans $3\times 10^4$ au with the velocities from 6.5 to 7.0 km s$^{-1}$. The bridge has the velocity gradient opposite to the streamer. Thus, the streamer is unlikely to be connected to this bridge, suggesting that the streamer does not have an accretion origin. We propose that a collision between a spherical core and the filament has shaped the density structure in this region, consequently triggering star formation within the head-tail-shaped core. In this core-filament collision (CFC) scenario, the collision appears to have fragmented the filament into two structures. The streamer is a bow structure, while the bridge is a remnant of the shock-compressed filament. Thus, we conclude that the Per-emb-2 streamer does not significantly contribute to the mass accumulation towards the protostar.