Discovery of interstellar anions in Cepheus star-forming region
  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.
