Tracing the evolutionary stage of Bok globules: CCS and NH3

TL;DR

This study investigates the chemical evolution of Bok globules by analyzing NH3 and CCS molecules, finding that the NH3/CCS ratio indicates a relatively evolved chemical state across different stages of star formation.

Contribution

It evaluates the applicability of the NH3/CCS abundance ratio as an evolutionary indicator specifically for isolated Bok globules, expanding previous research.

Findings

NH3/CCS ratio is roughly similar across all evolutionary stages.

No extremely high CCS abundance regions were found.

Observed Bok globules are in a relatively evolved chemical state.

Abstract

We pursue the investigation of a previously proposed correlation between chemical properties and physical evolutionary stage of isolated low-mass star-forming regions. In the past, the NH3/CCS abundance ratio was suggested to be a potentially useful indicator for the evolutionary stage of cloud cores. We aim to study its applicability for isolated Bok globules. A sample of 42 Bok globules with and without signs of current star formation was searched for CCS(2-1) emission, the observations were complemented with NH3 measurements available in the literature and own observations. The abundance ratio of both molecules is discussed with respect to the evolutionary stage of the objects and in the context of chemical models. The NH3/CCS ratio could be assessed for 18 Bok globules and is found to be moderately high and roughly similar across all evolutionary stages from starless and prestellar cores towards internally heated cores harbouring protostars of Class 0, Class I or later. Bok globules with extremely high CCS abundance analogous to carbon-chain producing regions in dark cloud cores are not found. The observed range of NH3/CCS hints towards a relatively evolved chemical state of all observed Bok globules.