Abstract
Context. The evolution of amorphous hydrocarbon materials, a-C(:H), principally resulting from ultraviolet (UV) photon absorption-induced processing, are likely at the heart of the variations in the observed properties of dust in the interstellar medium.
Highlights
The evolution of interstellar dust is a key but complex issue that is receiving some well-focussed attention
The latter scenario is similar to the recently-proposed mechanism for fullerene formation around planetary nebulae via the photo-processing and vibrational excitation of “arophatic” clusters derived from a-C:H particles formed in denser regions (Bernard-Salas et al 2012; Micelotta et al 2012)
From these works we note that the major observed trends and variations that need to be explained by any viable dust model are: 1. The FUV extinction rise and the intercept of an underlying linear component at infinite wavelength, in an E(λ − V)/E(B − V) vs. 1/λ plot, are very well correlated
Summary
The evolution of interstellar dust is a key but complex issue that is receiving some well-focussed attention. Hydrocarbon solids (i.e., a-C:H and a-C, known as HAC) present a particular challenge because of their inherent complexity and because they appear to be rather vulnerable to destruction (e.g., Serra Díaz-Cano & Jones 2008; Jones & Nuth 2011) They appear to undergo rather complex, sizedependent evolution arising, principally, from ultraviolet (UV) photon absorption leading to photo- or thermal-processing (e.g., Jones 2009, 2012a,b,c) and incident ion and electron collisions in shock waves and in a hot gas (e.g., Micelotta et al 2010a,b; Bocchio et al 2012). This paper uses a slightly-modified version of the laboratoryconstrained optEC(s)(a) data presented in Paper III, which naturally explain many of the observed properties attributed to carbonaceous dust in the ISM We insert these data into the DustEM dust extinction and emission calculator (Compiègne et al 2011) in order to quantitatively examine and explore. This paper is organised as follows: Sects. 2 and 3 summarise a-C(:H) dust photo-processing and its re-formation and re-accretion in the ISM, Sect. 4 briefly summarises the constraints imposed on dust models by experimental data and diffuse ISM dust observations, Sect. 5 presents our new evolutionary dust model, Sect. 6 discusses the astrophysical implications of the new model, Sect. 7 gives a schematic view of the a-C(:H) dust life-cycle and explores its evolution and variation in the ISM and Sect. 8 concludes this work
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