CCO has been detected first toward TMC-1:
M. Ohishi, H. Suzuki, S.-I. Ishikawa, C. Yamada, H. Kanamori, W. M. Irvine, R. D. Brown, P. D. Godfrey, N. Kaifu,
Detection of a new carbon-chain molecule, CCO
Astrophys. J. 380, L39–L42 (1991).
The N_J = 1₂ – 0₁ and 2₃ – 1₂ transitions were detected with the 43 m Green Bank telescope and the 45 m Nobeyama telecope, respectively, at 22258 and 45827 MHz.

R. G. Urso, M. E. Palumbo, C. Ceccarelli, N. Balucani, S. Bottinelli, C. Codella, F. Fontani, P. Leto, C. Trigilio, C. Vastel, R. Bachiller, G. A. Baratta, C. S. Buemi, E. Caux, A. Jaber Al-Edhari, B. Lefloch, A. López-Sepulcre, G. Umana, and L. Testi
reported on
C₂O and C₃O in Low-mass Star-forming Regions
Astron. Astrophys. 628, Art. No. A72 (2019).
The C₂O observations were carried out with the IRAM 30 m telescope at 3 mm. Three fine structure components of the N = 4 - 3 rotational transition around 92.5 GHz were detected toward the prestellar core L1544. Only the strongest of these components was searched for and detected toward the protostellar Elias 18.

H. E. Matthews, W. M. Irvine, P. Friberg, R. D. Brown, and P. D. Godfrey
reported on
A new Interstellar Molecule: Tricarbon Monoxide
Nature 310, 125–126 (1984).
The J = 2 − 1 transitions near 19.2 GHz was detected with good signal-to-noise ratio toward TMC-1 using the 43 m GBT.

R. D. Brown, P. D. Godfrey, D. M. Cragg, E. H. N. Rice, W. M. Irvine, P. Friberg, H. Suzuki, M. Ohishi, N. Kaifu, and M. Morimoto
extended the previous study subsequently in
Tricarbon Monoxide in TMC-1
Astrophys. J. 297, 302–308 (1985).
The J = 5 − 4, 8 − 7, and 9 − 8 transitions near 48.1, 77.0, and 86.6 GHz were detected using various telescopes.

The molecules was also detected in the circumstellar envelope of the C-rich AGB star CW Leonis by
E. D. Tenenbaum, A. J. Apponi, L. M. Ziurys, M. Agúndez, J. Cernicharo, J. R. Pardo, and M. Guélin
Detection of C₃O in IRC +10216: Oxygen-Carbon Chain Chemistry in the Outer Envelope
Astrophys. J. 649, L17–L20 (2006).
Observations were carried out at 3 and 2 mm using the ARO 12 m dish and a 3 mm using the IRAM 30 m telescope.

M. E. Palumbo, P. Leto, C. Siringo, and C. Trigilio
reported on the
Detection of C₃O in the Low-Mass Protostar Elias 18
Astrophys. J. 297, 302–308 (1985).
The Noto 32 m dish was employed to serach for the J = 4 − 3 transition near 38.5 GHz.

J. Cernicharo, M. Agúndez, C. Cabezas, B. Tercero, N. Marcelino, R. Fuentetaja, J. R. Pardo, and P. de Vicente
reported on the
Discovery of HCCCO and C₅O in TMC-1 with the QUIJOTE Line Survey
Astron. Astrophys. 656, Art. No. L21 (2021).
Oxopentatetraenylidene, C₅O, was identified through six rotational transitions with 11 ≤ J ≤ 17 in the course of a molecular line survey of the prototypical cold dark molecular cloud TMC-1 carried out with the Yebes 40 m radio telescope between 31.0 and 50.3 GHz. Four transitions were unblended or only slightly blended, two were somewhat more blended. A value of T_rot = 10.0 ± 0.5 K was derived through a rotation diagram. C₅O is about 50 times less abundant than C₂O and about 80 times less abundant than C₃O. Only upper limits were derived for C₄O and C₆O; these were in both cases higher than those of C₅O and thus not particularly constraining.

Contributor(s): H. S. P. Müller; 12, 2003; 09, 2012; 12, 2021