Hydrocarbon anions in interstellar clouds and circumstellar envelopes

TL;DR

This paper investigates the formation and abundance of hydrocarbon anions in interstellar and circumstellar environments, explaining recent detections and predicting new candidates for observation.

Contribution

It provides detailed modeling of hydrocarbon anion formation, reproduces observed column densities, and predicts additional detectable anions in various space regions.

Findings

C6H- abundance ratios can reach a few percent.

Models reproduce observed C6H- column densities in IRC+10216 and TMC-1.

C4H- and C8H- are predicted to be detectable in multiple astrophysical environments.

Abstract

The recent detection of the hydrocarbon anion C6H- in the interstellar medium has led us to investigate the synthesis of hydrocarbon anions in a variety of interstellar and circumstellar environments. We find that the anion/neutral abundance ratio can be quite large, on the order of at least a few percent, once the neutral has more than five carbon atoms. Detailed modeling shows that the column densities of C6H- observed in IRC+10216 and TMC-1 can be reproduced. Our calculations also predict that other hydrocarbon anions, such as C4H- and C8H-, are viable candidates for detection in IRC+10216, TMC-1 and photon-dominated regions such as the Horsehead Nebula.