An analysis of the isomers HCN and HNC in the evolution of high-mass star-forming regions

MARTINEZ, N. C.; PARON, S.

Ciudad Autónoma de Buenos Aires

Congreso; 64º REUNIÓN DE LA ASOCIACIÓN ARGENTINA DE ASTRONOMÍA; 2022

Asociación Argentina de Astronomía

The study of molecules and their chemistry in star-forming regions is fundamental to understand the physical process occurring in such regions. The HCN and HNC J=1-0 emissions were used to derive their integrated line intensities (I), to probe a relation recently appeared in the literature between the kinetic temperatures (T K) and the isomeric (I) ratio, and to obtain the isomers abundances (X) in 55 high-mass star-forming regions. These last ones are classified, according to the evolutive stage, as infrared dark clouds, high-mass protostellar objects, hot molecular cores, and ultracompact HII regions. It is inferred that the T K obtained from the isomeric integrated intensity ratio (I HCN/HNC ) are underestimated, and hence we suggest that this relation cannot be employed as an universal thermometer in the interstellar medium. The isomers abundances show a behavior that can be explained from the chemistry occurring as the temperature and the UV radiation increase according to the evolutive stage. We found that the abundance ratio (X HCN/HNC ) hardly could be used as a chemical clock, and we suggest that it can be approximated by I HCN/HNC. This work is part of an on-going study of multiple molecules that stand in the sample of analyzed regions which intends to contribute in the chemical knowledge of high-mass star formation.