TY - JOUR
T1 - Deep K-band Observations of TMC-1 with the Green Bank Telescope
T2 - Detection of HC7O, Nondetection of HC11N, and a Search for New Organic Molecules
AU - Cordiner, M. A.
AU - Charnley, S. B.
AU - Kisiel, Z.
AU - McGuire, B. A.
AU - Kuan, Y. J.
N1 - Publisher Copyright:
© 2017. The American Astronomical Society. All rights reserved.
PY - 2017/12/1
Y1 - 2017/12/1
N2 - 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.
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.
KW - ISM: abundances
KW - ISM: lines and bands
KW - ISM: molecules
KW - radio lines: ISM
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U2 - 10.3847/1538-4357/aa970c
DO - 10.3847/1538-4357/aa970c
M3 - Article
AN - SCOPUS:85037733926
SN - 0004-637X
VL - 850
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 187
ER -