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

TL;DR

This study investigates an exceptionally young Class 0 protostar, G204NE, to constrain the initial physical and chemical conditions of low-mass star formation. Using high-resolution ALMA Band 6 observations of 1.3 mm continuum and a suite of molecular tracers, the authors map the inner envelope, assess chemical stratification, and trace jets and outflows. They report a compact central structure with a small effective radius, absence of binarity down to 18 au, and a chemically stratified envelope showing CO depletion with a localized heated region, indicating an early evolutionary stage. The envelope exhibits rotating and infalling motions with a protostar mass around 0.08–0.1 solar masses, while a collimated outflow and high-velocity jets extend up to hundreds of au, launching within about twice the dust sublimation radius; the lack of a binary signature supports single-protostar driving the outflows, though a close companion cannot be entirely ruled out. The observed deflection of outflows and jets likely reflects turbulent accretion in a moderately magnetized core, providing insight into early protostellar environment interactions.

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.