Probing the Physical and Chemical Characteristics of an Extremely Early Class 0 Protostar in G204.4-11.3A2-NE

TL;DR

This study presents detailed ALMA observations of a very early-stage low-mass protostar in G204.4-11.3A2-NE, revealing its structure, chemical composition, kinematics, and outflow activity, indicating an initial protostellar phase with active jet launching.

Contribution

First detailed ALMA imaging of a Class 0 protostar in G204.4-11.3A2-NE, revealing its compact structure, chemical stratification, and jet/outflow characteristics in an early evolutionary stage.

Findings

Compact central structure of ~12 au radius without binarity down to 18 au

Chemical stratification with CO depletion in most regions

Detection of high-velocity jets up to 720 au in length

Abstract

We have observed the low-mass molecular cloud core G204.4-11.3A2-NE (G204NE) in the direction of Orion B giant molecular cloud with the Atacama Large Millimeter/submillimeter Array in Band 6. The $\rm 1.3\ mm$ continuum images and visibilities unveil a compact central structure with a radius of $\sim$12 au, while showing no signature of binarity down to 18 au. The bolometric temperature and luminosity of this source are derived to be ${\sim}$33 K and $\sim$1.15 $~L_{\odot}$, respectively. Chemical stratification is observed in dense gas tracers, with C$^{18}$O emission peaking at the continuum position surrounded by the spatially extended emission of N$_2$D$^+$ and DCO$^+$. This implies that the core is in a very early evolutionary stage in which $\rm CO$ depletion occurs in most regions except for a small area heated by the central source. The envelope kinematics indicates a rotating and infalling structure with a central protostar mass of 0.08-0.1 $M_{\odot}$. The protostar drives a collimated outflow traced by CO, SiO, SO, and H$_2$CO, with misaligned blueshifted and redshifted lobes exhibiting a pair of bow-like patterns. High-velocity jets, extending up to 720 au, are detected in CO, SiO, and SO lines. The jet launching region is likely within twice of the dust sublimation zone. The absence of a binary signature suggests the outflows and jets are driven by a single protostar, although a close binary cannot be ruled out. The observed deflection of the outflows and jet is likely due to turbulent accretion in a moderately magnetized core.