A Substellar-Mass Protostar and its Outflow of IRAS 15398-3359 Revealed by Subarcsecond-Resolution Observations of H$_2$CO and CCH

TL;DR

This study uses high-resolution ALMA observations to reveal the structure and outflow geometry of the low-mass protostar IRAS 15398-3359, providing insights into its infall, outflow, and potential disk formation.

Contribution

First detailed subarcsecond imaging of H$_2$CO and CCH around IRAS 15398-3359, revealing outflow inclination and infalling envelope characteristics.

Findings

Detected a compact core and well-collimated outflow cavity.

Outflow inclination estimated at about 20°, nearly edge-on.

Protostar mass estimated to be less than 0.09 solar masses.

Abstract

Sub-arcsecond ($0.^{\prime\prime}5$) images of H$_2$CO and CCH line emission have been obtained in the $0.8$ mm band toward the low-mass protostar IRAS 15398-3359 in the Lupus 1 cloud as one of the Cycle 0 projects of the Atacama Large Millimeter/Submillimeter Array. We have detected a compact component concentrated in the vicinity of the protostar and a well-collimated outflow cavity extending along the northeast-southwest axis. The inclination angle of the outflow is found to be about $20^\circ$, or almost edge-on, based on the kinematic structure of the outflow cavity. This is in contrast to previous suggestions of a more pole-on geometry. The centrally concentrated component is interpreted by use of a model of the infalling rotating envelope with the estimated inclination angle, and the mass of the protostar is estimated to be less than $0.09\ M_\odot$. Higher spatial resolution data are needed to infer the presence of a rotationally supported disk for this source, hinted at by a weak high-velocity H$_2$CO emission associated with the protostar.