One-dimensional and time-dependent modelling of complex organic molecules in protostars

TL;DR

This paper presents an improved one-dimensional, time-dependent model of complex organic molecules in protostars, capable of interpreting diverse observational data and revealing insights into their formation environments.

Contribution

The authors enhanced the UCLCHEM code to better simulate COMs in protostars, incorporating radiative effects and temperature coupling, enabling more accurate interpretation of observations.

Findings

The model successfully reproduces observations from various star-forming regions.

COMs are found at different temperatures in the envelope, affecting interpretation.

In SgrB2(N1), a high cosmic-ray ionisation rate is indicated.

Abstract

Complex organic molecules (COMs), the building blocks of life, have been extensively detected under various physical conditions, from quiescent clouds to star-forming regions. They therefore serve as excellent tracers for the local physical and chemical properties of these environments. Proper models that are capable of grasping the formation and destruction of COMs are crucial to understanding observations. However, given that distinct COMs may be detected from different locations and at varying times, we improve UCLCHEM - a gas-grain chemical code - to a one-dimensional, time-dependent model, tailored to protostars. In this update, we examine two stages of a protostar: the prestellar and heating stages, incorporating a simple radiative mechanism for both the internal and external radiation fields of the cloud. This approach relies on the key assumption that the dust and gas temperatures are completely coupled. Ultimately, we implement an updated version of our model to interpret observations obtained through both single-dish and interferometry under varying conditions, including a SgrB2(N1) hot core, massive Galactic clumps and a hot core in Orion. We show that our model could reproduce these observations well, highlighting that some COMs are positioned at a higher temperature in the envelope, whereas others are from the lower temperature, potentially leading to misinterpretation when using a single-point model. In a particular case of SgrB2(N1), the best model indicates that the cosmic-ray ionisation rate significantly exceeds the value typically used for the standard interstellar medium. Our model shows as an efficient computational tool particularly useful for better insights into observations of COMs.