A coincidence between a hydrocarbon plasma absorption spectrum and the lambda 5450 DIB

TL;DR

This study links a broad diffuse interstellar band at 5450 nm to a laboratory spectrum of an expanding acetylene plasma, suggesting a molecular transient containing carbon and hydrogen as the carrier, though not definitively identified.

Contribution

It provides the first laboratory-observation match for the 5450 DIB, narrowing down potential molecular carriers and demonstrating the relevance of plasma spectra to interstellar features.

Findings

Laboratory spectrum coincides with astronomical DIB at 5450 nm.

The DIB has a FWHM of approximately 0.95 nm.

The carrier is likely a carbon-hydrogen molecular transient.

Abstract

The aim of this work is to link the broad lambda 5450 diffuse interstellar band (DIB) to a laboratory spectrum recorded through an expanding acetylene plasma. Cavity ring-down direct absorption spectra and astronomical observations of HD 183143 with the HERMES spectrograph on the Mercator Telescope in La Palma and the McKellar spectrograph on the DAO 1.2 m Telescope are compared. In the 543-547 nm region a broad band is measured with a band maximum at 545 nm and FWHM of 1.03(0.1) nm coinciding with a well-known diffuse interstellar band at lambda 5450 with FWHM of 0.953 nm. 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 has been performed in order to unambiguously identify the laboratory carrier of this band. This has not been possible. The laboratory results, however, restrict the carrier to a molecular transient, consisting of carbon and hydrogen.