This article has an erratum: [erratum]
Volume 540, April 2012
|Number of page(s)||21|
|Section||Interstellar and circumstellar matter|
|Published online||13 March 2012|
Variations on a theme – the evolution of hydrocarbon solids
Institut d’Astrophysique Spatiale, CNRS, IAS UMR8617, 91405 Orsay, France
Université Paris Sud, IAS UMR8617, Orsay 91405, France
Received: 4 July 2011
Accepted: 30 October 2011
Context. The properties of hydrogenated amorphous carbon (a-C:H) dust are known to evolve in response to the local conditions.
Aims. We present an adaptable model for the determination of the optical properties of low-temperature, interstellar a-C:H grains that is based on the fundamental physics of their composition.
Methods. The imaginary part of the refractive index, k, for a-C:H materials, from 50 eV to cm wavelengths, is derived and the real part, n, of the refractive index is then calculated using the Kramers-Kronig relations.
Results. The formulated optEC(s) model allows a determination of the complex dielectric function, ϵ, and refractive index, m(n,k), for a-C:H materials as a continuous function the band gap, Eg, which is shown to lie in the range ≃−0.1 to 2.7 eV. We provide expressions that enable a determination of their optical constants and tabulate m(n,k,Eg) for 14 different values of Eg. We explore the evolution of the likely extinction and emission behaviours of a-C:H grains and estimate the relevant transformation time-scales.
Conclusions. With the optEC(s) model we are able to predict how the optical properties of an a-C:H dust component in the interstellar medium will evolve in response to, principally, the local interstellar radiation field. The evolution of a-C:H materials appears to be consistent with many dust extinction, absorption, scattering and emission properties, and also with H2 molecule, daughter “PAH” and hydrocarbon molecule formation resulting from its photo-driven decomposition.
Key words: dust, extinction / ISM: general
Appendices A and B are available in electronic form at http://www.aanda.org
Data files are available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (22.214.171.124) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/540/A2
© ESO, 2012
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.