Abstract
Carriers of diffuse interstellar bands (DIBs) still need to be identified. In a recent paper, we reported a correlation between the DIB wavelength and the apparent UV resilience (or boost) of their carriers. We proposed that this might be an indication of the important role of conjugated elongated molecules among the DIB carriers. The aim of this paper is to further understand the origin of this correlation. The analysis of 509 optical DIBs on the lines of sight of HD 183143 and/or HD 204827 reported in the literature shows that this correlation mainly implies the 386 narrow DIBs with a band width <1.1 Å, which include most of the identified DIBs of the C2andζfamilies, while the majority of the 123 broader DIBs, including the identifiedσDIBs, do not display such a correlation. We present a possible origin of this correlation from very strong bands of large conjugated elongated molecules, such as carbon chains, polyacenes, or other catacondensed polycyclic aromatic hydrocarbons. The total amount of carbon contained in all the carriers of these narrow DIBs is a very small fraction of the interstellar carbon if their oscillator strengths are ≥1. The amount of carbon locked in the carriers of the broader DIBs is higher, especially if their oscillator strengths are significantly weaker.
Highlights
Identification of carriers of the diffuse interstellar bands (DIBs) remains an outstanding problem in astrophysics, and to this day, only five bands have been attributed to an identified carrier, C+60 (Foing & Ehrenfreund 1994; Campbell et al 2015, 2016)
The analysis of 509 optical DIBs on the lines of sight of HD 183143 and/or HD 204827 reported in the literature shows that this correlation mainly implies the 386 narrow DIBs with a band width
We present a possible origin of this correlation from very strong bands of large conjugated elongated molecules, such as carbon chains, polyacenes, or other catacondensed polycyclic aromatic hydrocarbons
Summary
Identification of carriers of the diffuse interstellar bands (DIBs) remains an outstanding problem in astrophysics (see e.g. Herbig 1975, 1995; Sarre 2006; Tielens & Snow 1995; and especially Cami & Cox 2014; see e.g. Omont 2016; Fan et al 2017, 2019; Cami et al 2018 for more recent references), and to this day, only five bands have been attributed to an identified carrier, C+60 (Foing & Ehrenfreund 1994; Campbell et al 2015, 2016). The higher EW(5797)/EW(5780) DIB ratio values, such as are observed towards HD 204827, are found only for lower inferred UV intensities (Welty 2014) This λ/UV correlation could be explained by the combined dependence on the wavelength of the strong optical bands of polyacenes and the UV photodissociation on their length. As pointed out in OBT19, various elongated molecules with π electron conjugated systems should display a similar correlation We here explore this possibility especially for the catacondensed PAHs and the long carbon chains.
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