Fundamental aspects of episodic accretion chemistry explored with single-point models

TL;DR

This study uses single-point chemical models to investigate how episodic accretion in low-mass protostars influences envelope chemistry, especially CO abundance, and proposes chemical tracers for accretion history.

Contribution

It introduces a set of models linking episodic accretion events to chemical signatures, highlighting CO as a key tracer of past accretion bursts.

Findings

CO ice sublimates during accretion bursts

Excess gas-phase CO persists for 10^3-10^4 years after bursts

Chemical signatures can reveal episodic accretion history

Abstract

We explore a set of single-point chemical models to study the fundamental chemical aspects of episodic accretion in low-mass embedded protostars. Our goal is twofold: (1) to understand how the repeated heating and cooling of the envelope affects the abundances of CO and related species; and (2) to identify chemical tracers that can be used as a novel probe of the timescales and other physical aspects of episodic accretion. We develop a set of single-point models that serve as a general prescription for how the chemical composition of a protostellar envelope is altered by episodic accretion. The main effect of each accretion burst is to drive CO ice off the grains in part of the envelope. The duration of the subsequent quiescent stage (before the next burst hits) is similar to or shorter than the freeze-out timescale of CO, allowing the chemical effects of a burst to linger long after the burst has ended. We predict that the resulting excess of gas-phase CO can be observed with single-dish or interferometer facilities as evidence of an accretion burst in the past 10^3 - 10^4 yr.