VUV spectroscopy of carbon dust analogs: contribution to interstellar extinction

Abstract

A full spectral characterization of carbonaceous dust analogs is necessary to understand their potential as carriers of observed astronomical spectral signatures such as the ubiquitous UV bump at 217.5 nm and the far-ultraviolet (FUV) rise common to interstellar extinction curves. Our goal is to study the spectral properties of carbonaceous dust analogs from the FUV to the mid-infrared (MIR) domain. We seek in particular to understand the spectra of these materials in the FUV range, for which laboratory studies are scarce. We produced analogs to carbonaceous interstellar dust encountered in various phases of the interstellar medium: amorphous hydrogenated carbons (a-C:H), for carbonaceous dust observed in the diffuse interstellar medium, and soot particles, for the polyaromatic component. Analogs to a-C:H dust were produced using a radio-frequency plasma reactor at low pressures, and soot nanoparticles films were produced in an ethylene (C${}_2$H${}_4$) flame. We measured transmission spectra of these thin films (thickness < 100 nm) in the far-ultraviolet (190 - 250 nm) and in the vacuum-ultraviolet (VUV; 50 - 190 nm) regions using the APEX chamber at the DISCO beam line of the SOLEIL synchrotron radiation facility. These were also characterized through infrared microscopy at the SMIS beam line. We successfully measured the transmission spectra of these analogs from λ = 1 μm to 50 nm. From these, we extracted the laboratory optical constants via Kramers-Kronig inversion. We used these constants for comparison to existing interstellar extinction curves. We extend the spectral measurements of these types of carbonaceous analogs into the VUV and link the spectral features in this range to the 3.4 μm band. We suggest that these two materials might contribute to different classes of interstellar extinction curves.

10 pages, 10 figures, accepted to Astronomy & Astrophysics on 13/11/2015

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Cited by in corpus (7)

• The global dust modelling framework THEMIS (The Heterogeneous dust Evolution Model for Interstellar Solids)
• Photochemical hazes dramatically alter temperature structure and atmospheric circulation in 3D simulations of hot Jupiters
• Polyaromatic disordered carbon grains as carriers of the UV bump: FUV to mid-infrared spectroscopy of laboratory analogs
• Hazy with a chance of star spots: constraining the atmosphere of the young planet, K2-33b
• Carbon 'fluffy' aggregates produced by helium - hydrocarbon high pressure plasmas as analogs to interstellar dust
• Hydrogenated amorphous carbon grains as an alternative carrier of the 9$-$13$\mu$m plateau feature in the fullerene planetary nebula Tc 1
• Vacuum ultraviolet photolysis of hydrogenated amorphous carbons. III. Diffusion of photo-produced H2 as a function of temperature