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

Abstract

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. It has been suggested previous episodic accretion events by this source. Furthermore, the analysis of the morphology and kinematics of the molecular outflow revealed the presence of four $^{12}$CO(2-1) bipolar elliptical shock-like structures identified in both lobes. These structures seem to trace different ejections inclined $\sim$10\deg on the plane of the sky from each other. This led to the hypothesis that the outflow axis likely precesses and launches material episodically. We analyze ALMA archive observations in Band 6, revealing the presence of low-velocity ($<3.5$km s$^{-1}$) emission from the line $^{12}$CO(2-1) to the south and north of the protostar. We study the morphology and kinematics of the gas, which seems to support the hypothesis of a precessing episodic outflow. The ALMA observations reveal a north-south (N-S) outflow most likely associated with the IRAS 15398-3359 protostellar system. This outflow could be older than the well-studied NE-SW outflow. The orientation of the N-S outflow is 50\deg - 60\deg on the plane of the sky away from that of the NE-SW outflow. We also analyze the Spectral Energy Distribution of a far away young star and preliminary discard it as the driver of the SE outflow remnants. 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 by the same protostar.