Episodicity in accretion-ejection processes associated with IRAS 15398-3359

Abstract

Context. The protostar IRAS 15398-3359 is associated with a bipolar molecular outflow ejected in an nearly northeast–southwest (NE–SW) direction, which has been extensively studied. Previous episodic accretion events have been suggested by this source. Furthermore, the analysis of the morphology and kinematics of the molecular outflow revealed the presence of four 12CO (2–1) bipolarelliptical shock-like structures identified in both lobes. These structures seem to trace different ejections inclined ∼10◦from each otheron the plane of the sky. This led to the hypothesis that the outflow axis likely precesses and launches material episodically. Aims. Since several authors reached the conclusion of the same episodicity scenario by independent observations, IRAS 15398-3359has become an ideal target to empirically analyze the relationship between accretion and ejection processes.Methods. We analyzed ALMA archive observations in Band 6, revealing the presence of low-velocity (<3.5 km s−1) emission fromthe 12CO (2–1) line to the south and north of the protostar. We studied the morphology and kinematics of the gas; our study seems tosupport the hypothesis of a precessing episodic outflow.Results. The ALMA observations reveal a north–south (N–S) outflow most likely associated with the IRAS 15398-3359 protostellarsystem. This outflow could be older than the well-studied NE–SW outflow. The orientation of the N–S outflow is 50◦–60◦ on the planeof the sky away from that of the NE–SW outflow. We also analyzed the spectral energy distribution of a far away young star andpreliminarily discard it as the driver of the SE outflow remnants. Conclusions. The new observations support the hypothesis of strong episodic accretion-ejection events in IRAS 15398-3359, accompanied by dramatic changes in the orientation of its ejection axis, implying that all the outflows in the region may have been driven bythe same protostar