2010A&A...511L...3L

The aim of this work is to link the broad λ5450 diffuse interstellar band (DIB) to a laboratory spectrum recorded through expanding acetylene plasma. Cavity ring-down direct absorption spectra and astronomical observations of HD 183143 with the HERMES spectrograph on the Mercator Telescope on La Palma and the McKellar spectrograph on the DAO 1.2m Telescope are compared. In the 543-547nm region a broad band is measured with a band maximum at 545nm and FWHM of 1.03(0.1)nm coinciding with a well-known diffuse interstellar band at λ5450 with an FWHM of 0.953nm. A coincidence is found between the laboratory and the two independent observational studies obtained at higher spectral resolution. This result is important, as a match between a laboratory spectrum and a - potentially lifetime broadened - DIB is found. A series of additional experiments were performed in order to unambiguously identify the laboratory carrier of this band, but this was not successful. The laboratory results, however, restrict the carrier to a molecular transient, consisting of carbon and hydrogen.