Discovery of interstellar anions in Cepheus star-forming region

TL;DR

This paper reports the first detection of interstellar anions and long-chain molecules in the Cepheus star-forming region, expanding understanding of complex chemistry in star-forming environments and highlighting the widespread presence of anions in dense interstellar clouds.

Contribution

It presents the first detection of interstellar anions and long-chain polyynes in Cepheus, demonstrating their significance in star formation chemistry outside Taurus.

Findings

Detection of C6H- and C6H in Cepheus star-forming region.

Anion-to-neutral ratios of about 4%, consistent across different clouds.

Rotational temperatures of 6.2 K and 8.7 K in the observed regions.

Abstract

We report the detection of microwave emission lines from the hydrocarbon anion C6H- and its parent neutral C6H in the star-forming region L1251A (in Cepheus), and the pre-stellar core L1512 (in Auriga). The carbon-chain-bearing species C4H, HC3N, HC5N, HC7N and C3S are also detected in large abundances. The observations of L1251A constitute the first detections of anions and long-chain polyynes and cyanopolyynes (with more than 5 carbon atoms) in the Cepheus Flare star-forming region, and the first detection of anions in the vicinity of a protostar outside of the Taurus molecular cloud complex, highlighting a wider importance for anions in the chemistry of star formation. Rotational excitation temperatures have been derived from the HC3N hyperfine structure lines, and are found to be 6.2 K for L1251A and 8.7 K for L1512. The anion-to-neutral ratios are 3.6% and 4.1%, respectively, which are within the range of values previously observed in the interstellar medium, and suggest a relative uniformity in the processes governing anion abundances in different dense interstellar clouds. This research contributes towards the growing body of evidence that carbon chain anions are relatively abundant in interstellar clouds throughout the Galaxy, but especially in the regions of relatively high density and high depletion surrounding pre-stellar cores and young, embedded protostars.