===== On Indene in the ISM =====

J. Cernicharo, M. Agúndez, C. Cabezas, B. Tercero, N. Marcelino, J. R. Pardo, and P. de Vicente\\
reported on\\
**[[https://doi.org/10.1051/0004-6361/202141156|Pure hydrocarbon cycles in TMC-1: Discovery of ethynylcyclopropenylidene, cyclopentadiene, and indene]]**\\
//Astron. Astrophys.// **649**, Art. No. L15 (2021).\\
Indene, //c//-C<sub>9</sub>H<sub>8</sub>, was identified as the first pure polycyclic aromatic hydrocarbon through a large number of mostly //a//-type lines with 10 ≤ //J// ≤ 20 and //K<sub>a</sub>// ≤ 6 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 32.8 and 49.2 GHz. A substantial fraction of the lines was unblended or slightly blended. A value of //T//<sub>rot</sub> = 10 K was assumed. The column density of indene is about the same as cyclopentadienene or the C<sub>4</sub>H<sub>4</sub> isomers butenyne and ethynylallene. It is about a factor of 7 lower than that of C<sub>3</sub>H<sub>3</sub>.\\

A. M. Burkhardt, K. L. K. Lee, P. B. Changala, C. N. Shingledecker, I. R. Cooke, R. A. Loomis, H. Wei, S. B. Charnley, E. Herbst, M. C. McCarthy, and B. A. McGuire\\
submitted a report somewhat earlier but that appeared later on the\\
**[[https://doi.org/10.3847/2041-8213/abfd3a|Discovery of the pure polycyclic aromatic hydrocarbon indene (//c//-C<sub>9</sub>H<sub>8</sub>) with GOTHAM observations of TMC-1]]**\\
//Astrophys. J. Lett.// **913**, Art. No. L18 (2021).\\
The observations were obtained in the course of the line survey Green Bank Telescope Observations of TMC-1: Hunting for Aromatic Molecules. The data were recorded with very high resolution which resolves, at least in part, the complex velocity structure . No individual lines were detected, as usually in this survey. Stacking of all lines of all four major velocity components, however, yielded a signal slighly above 5σ. Note, however, that this method becomes questionable with weak lines as those of indene. As can be seen in Fig. 4 of the previous paper, TMC-1 is not line poor anymore at 1 cm wavelength on the level of the indene lines; the situation **may** be slightly better at longer wavelengths. The derived column densities of the two reports agree.\\


----

Contributor(s): H. S. P. Müller; 05, 2021

----