Hot methanol in the [BHB2007] 11 protobinary system: hot corino versus shock origin? : FAUST V

TL;DR

This study uses ALMA data to analyze methanol emission in the [BHB2007] 11 protobinary system, revealing hot, dense, and methanol-rich gas likely originating from shocks caused by filament inflows, with implications for star formation chemistry.

Contribution

It provides the first detailed analysis of methanol emission in a protobinary system, highlighting shock-related origins and the impact of dust opacity on line detection.

Findings

Methanol emission is compact and encompasses both protostars.

Gas is hot, dense, and highly enriched in methanol, with abundance up to 1e-5.

Methanol likely originates from shocks due to filament inflows.

Abstract

Methanol is a ubiquitous species commonly found in the molecular interstellar medium. It is also a crucial seed species for the building-up of the chemical complexity in star forming regions. Thus, understanding how its abundance evolves during the star formation process and whether it enriches the emerging planetary system is of paramount importance. We used new data from the ALMA Large Program FAUST (Fifty AU STudy of the chemistry in the disk/envelope system of Solar-like protostars) to study the methanol line emission towards the [BHB2007] 11 protobinary system (sources A and B), where a complex structure of filaments connecting the two sources with a larger circumbinary disk has been previously detected. Twelve methanol lines have been detected with upper energies in the range [45-537] K along with one 13CH3OH transition. The methanol emission is compact and encompasses both protostars, separated by only 28 au and presents three velocity components, not spatially resolved by our observations, associated with three different spatial regions, with two of them close to 11B and the third one associated with 11A. A non-LTE radiative transfer analysis of the methanol lines concludes that the gas is hot and dense and highly enriched in methanol with an abundance as high as 1e-5. Using previous continuum data, we show that dust opacity can potentially completely absorb the methanol line emission from the two binary objects. Although we cannot firmly exclude other possibilities, we suggest that the detected hot methanol is resulting from the shocked gas from the incoming filaments streaming towards [BHB2007] 11 A and B, respectively. Higher spatial resolution observations are necessary to confirm this hypothesis.