Carbonaceous nano-dust emission in proto-planetary discs: the aliphatic-aromatic components★
Institut d’Astrophysique Spatiale (IAS), UMR 8617-CNRS, Université Paris Sud,
91405 Orsay, France
2 Institut des Sciences Moléculaires d’Orsay (ISMO), CNRS, Université Paris Sud, Université Paris-Saclay, 91405 Orsay, France
Accepted: 17 January 2019
Context. In the interstellar medium, carbon (nano-)grains are a major component of interstellar dust. This solid phase is more vulnerable to processing and destruction than its silicate counterpart. It exhibits a complex, size-dependent evolution that is due to interactions within different radiative and dynamical environments. Infrared signatures of these carbon nano-grains are seen in a large number of discs around Herbig HAeBe stars.
Aims. We probe the composition and evolution of carbon nano-grains at the surface of (pre-)transitional proto-planetary discs around Herbig stars.
Methods. We present spatially resolved infrared emission spectra obtained with the Nasmyth Adaptive Optics System (NAOS) Near-Infrared Imager and Spectrograph (CONICA) at the Very Large Telescope (VLT) in the 3–4 μm range with a spatial resolution of 0.1′′, which allowed us to trace aromatic, olefinic, and aliphatic bands that are attributed to sub-nanometer hydrocarbon grains. We applied a Gaussian fitting to analyse the observed spectral signatures. Finally, we propose an interpretation in the framework of the The Heterogeneous dust Evolution Model of Interstellar Solids (THEMIS).
Results. We show the presence of several spatially extended spectral features that are related to aromatic and aliphatic hydrocarbon material in discs around Herbig stars, from ~10 to 50–100 au, and even in inner gaps that are devoid of large grains. The correlation and constant intensity ratios between aliphatic and aromatic CH stretching bands suggests a common nature of the carriers. Given their expected high destruction rates through UV photons, our observations suggest that they are continuously replenished at the disc surfaces.
Key words: protoplanetary disks / infrared: planetary systems
The reduced spectra (Fig. 2) are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (188.8.131.52) or via https://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/623/A135
© T. Boutéraon et al. 2019
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.