CCO has been detected first toward TMC-1:
M. Ohishi, S.-I. Ishikawa, C. Yamada, H. Kanamori, W. M. Irvine, R. D. Brown, P. D. Godfrey, N. Kaifu, H. Suzuki,
Detection of a new carbon-chain molecule, CCO
Astrophys. J. 290, L65L66 (1985).
The NJ = 12 01 and 23 12 transitions werev detected with the 43 m Green Bank telescope and the 45 m Nobeyama telecope, respectively, at 22258 and 45827 MHz.