Cyanopolyynes and sulphur bearing species in hot cores: Chemical and line excitation models

TL;DR

This study models the chemistry and line excitation in hot cores, revealing that long-chain cyanopolyynes can form under such conditions and may serve as chemical clocks, with implications for interpreting spectral data.

Contribution

It introduces a chemical and excitation model demonstrating formation of long-chain cyanopolyynes in hot cores and their potential as age indicators, expanding understanding of hot core chemistry.

Findings

Long-chain cyanopolyynes can form in hot cores.

Cyanopolyynes' abundances are linked to acetylene evaporation.

Line ratios help interpret spectral data.

Abstract

We present results from a time dependent gas phase chemical model of a hot core based on the physical conditions of G305.2+0.2. While the cyanopolyyne HC_3N has been observed in hot cores, the longer chained species, HC_5N, HC_7N, and HC_9N have not been considered typical hot core species. We present results which show that these species can be formed under hot core conditions. We discuss the important chemical reactions in this process and, in particular, show that their abundances are linked to the parent species acetylene which is evaporated from icy grain mantles. The cyanopolyynes show promise as `chemical clocks' which may aid future observations in determining the age of hot core sources. The abundance of the larger cyanopolyynes increase and decrease over relatively short time scales, ~10^2.5 years. We also discuss several sulphur bearing species. We present results from a non-LTE statistical equilibrium excitation model as a series of density, temperature and column density dependent contour plots which show both the line intensities and several line ratios. These aid in the interpretation of spectral line data, even when there is limited line information available.