Deep K-band Observations of TMC-1 with the Green Bank Telescope: Detection of HC7O, Nondetection of HC11N, and a Search for New Organic Molecules

M. A. Cordiner, S. B. Charnley, Z. Kisiel, B. A. McGuire, Y. J. Kuan

Research output: Contribution to journalArticle

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Abstract

The 100 m Robert C. Byrd Green Bank Telescope K-band (KFPA) receiver was used to perform a high-sensitivity search for rotational emission lines from complex organic molecules in the cold interstellar medium toward TMC-1 (cyanopolyyne peak), focussing on the identification of new carbon-chain-bearing species as well as molecules of possible prebiotic relevance. We report a detection of the carbon-chain oxide species HC7O and derive a column density of cm-2. This species is theorized to form as a result of associative electron detachment reactions between oxygen atoms and C7H-, and/or reaction of C6H2 + with CO (followed by dissociative electron recombination). Upper limits are given for the related HC6O, C6O, and C7O molecules. In addition, we obtained the first detections of emission from individual 13C isotopologues of HC7N, and derive abundance ratios HC7N/HCCC13CCCCN =110 ±16 and HC7N/HCCCC13CCCN =96 ±11, indicative of significant 13C depletion in this species relative to the local interstellar elemental 12C/13C ratio of 60-70. The observed spectral region covered two transitions of HC11N, but emission from this species was not detected, and the corresponding column density upper limit is 7.4 × 1010 cm-2 (at 95% confidence). This is significantly lower than the value of previously claimed by Bell et al. and confirms the recent nondetection of HC11N in TMC-1 by Loomis et al. Upper limits were also obtained for the column densities of malononitrile and the nitrogen heterocycles quinoline, isoquinoline, and pyrimidine.

Original languageEnglish
Article number187
JournalAstrophysical Journal
Volume850
Issue number2
DOIs
Publication statusPublished - 2017 Dec 1

Fingerprint

extremely high frequencies
telescopes
malononitrile
electron recombination
molecules
carbon
quinoline
pyrimidines
detachment
confidence
oxygen atoms
depletion
receivers
electron
nitrogen
oxides
sensitivity
recombination
detection
oxide

Keywords

  • ISM: abundances
  • ISM: lines and bands
  • ISM: molecules
  • radio lines: ISM

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Deep K-band Observations of TMC-1 with the Green Bank Telescope : Detection of HC7O, Nondetection of HC11N, and a Search for New Organic Molecules. / Cordiner, M. A.; Charnley, S. B.; Kisiel, Z.; McGuire, B. A.; Kuan, Y. J.

In: Astrophysical Journal, Vol. 850, No. 2, 187, 01.12.2017.

Research output: Contribution to journalArticle

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AU - Charnley, S. B.

AU - Kisiel, Z.

AU - McGuire, B. A.

AU - Kuan, Y. J.

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AB - The 100 m Robert C. Byrd Green Bank Telescope K-band (KFPA) receiver was used to perform a high-sensitivity search for rotational emission lines from complex organic molecules in the cold interstellar medium toward TMC-1 (cyanopolyyne peak), focussing on the identification of new carbon-chain-bearing species as well as molecules of possible prebiotic relevance. We report a detection of the carbon-chain oxide species HC7O and derive a column density of cm-2. This species is theorized to form as a result of associative electron detachment reactions between oxygen atoms and C7H-, and/or reaction of C6H2 + with CO (followed by dissociative electron recombination). Upper limits are given for the related HC6O, C6O, and C7O molecules. In addition, we obtained the first detections of emission from individual 13C isotopologues of HC7N, and derive abundance ratios HC7N/HCCC13CCCCN =110 ±16 and HC7N/HCCCC13CCCN =96 ±11, indicative of significant 13C depletion in this species relative to the local interstellar elemental 12C/13C ratio of 60-70. The observed spectral region covered two transitions of HC11N, but emission from this species was not detected, and the corresponding column density upper limit is 7.4 × 1010 cm-2 (at 95% confidence). This is significantly lower than the value of previously claimed by Bell et al. and confirms the recent nondetection of HC11N in TMC-1 by Loomis et al. Upper limits were also obtained for the column densities of malononitrile and the nitrogen heterocycles quinoline, isoquinoline, and pyrimidine.

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KW - ISM: molecules

KW - radio lines: ISM

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