Discovery of interstellar anions in Cepheus star-forming region

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.

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• The Possible Interstellar Anion CH2CN-: Spectroscopic Constants, Vibrational Frequencies, and Other Considerations
• The abundance and excitation of molecular anions in interstellar clouds
• Carbon-Chain Species in Warm-up Models
• Organic chemistry of low-mass star-forming cores I: 7 mm spectroscopy of Chamaeleon MMS1
• Gas-grain models for interstellar anion chemistry
• The connection between warm carbon chain chemistry and interstellar irradiation of star-forming cores
• Cyanopolyyne chemistry in the L1544 prestellar core: new insights from GBT observations
• Electronic and Rovibrational Quantum Chemical Analysis of C${}_3$P${}^{-}$: The Next Interstellar Anion?
• Carbon-Chain Molecules in Molecular Outflows and Lupus I Region--New Producing Region and New Forming Mechanism
• A search for cloud cores affected by shocked carbon chain chemistry in L1251
• A particular carbon-chain-producing region: L1489 starless core
• Modelling carbon-chain species formation in lukewarm corinos with new multi-phase models
• Modeling the role of electron attachment rates on column density ratios for CnH-/CnH (n=4,6,8) in dense molecular clouds