PAHs in Astronomy - A Review

Salama, Farid

doi:10.1017/s1743921308021960

Cited by 51 publications

(29 citation statements)

References 36 publications

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“…In particular, polycyclic aromatic hydrocarbons (PAHs) and fullerenes are proposed as candidates for the DIB carriers (See recent assessment by Salama et al 1996). The presence of these large molecules in the ISM has been confirmed from their mid-infrared emission features in various astrophysical environments (Salama 2008;Tielens 2008).…”

Section: Dib Polarisation Limitsmentioning

confidence: 99%

Linear and circular spectropolarimetry of diffuse interstellar bands

Cox

Ehrenfreund

Foing

et al. 2011

A&A

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Context. The identification of the carriers of diffuse interstellar bands (DIBs) remains one of the long-standing mysteries in astronomy. The detection of a polarisation signal in a DIB profile can be used to distinguish between a dust or gas-phase carrier. The polarisation profile can give additional information on the grain or molecular properties of the absorber. Aims. To measure the polarisation efficiency of the carriers of the diffuse interstellar bands. Methods. In order to detect and measure the linear and circular polarisation of the DIBs we observed reddened lines of sight showing continuum polarisation. For this study we selected two stars HD 197770 and HD 194279. We used high-resolution (R ∼ 64 000) spectropolarimetry in the wavelength range from 3700 to 10 480 Å with the ESPaDOnS échelle spectrograph mounted at the CFHT. Results. High S/N and high resolution Stokes V (circular), Q and U (linear) spectra were obtained. We constrained upper limits by a factor of 10 for previously observed DIBs. Furthermore, we analysed ∼30 additional DIBs for which no spectropolarimetry data has been obtained before. This included the 9577 Å DIB and the 8621 Å DIB. The former is attributed to the C + 60 fullerene, which could become aligned in a magnetic field. The latter shows a tight correlation with the amount of dust in the line-of-sight and therefore most likely may show a polarisation signal related the aligned grains. Conclusions. The lack of polarisation in 45 DIB profiles suggests that none of the absorption lines is induced by a grain-type carrier. The strict upper limits, less than ∼0.01%, derived for the observed lines-of-sight imply that if DIBs are due to gas-phase molecules these carriers have polarisation efficiencies which are at least 6 times, and up to 300 times, smaller than those predicted for grainrelated carriers.

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Section: Dib Polarisation Limitsmentioning

confidence: 99%

Linear and circular spectropolarimetry of diffuse interstellar bands

Cox

Ehrenfreund

Foing

et al. 2011

A&A

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“…Polycyclic aromatic hydrocarbons (PAHs) are believed to represent a significant reservoir of interstellar elemental carbon ( f c ∼ 3.5 × 10 −2 , Tielens 2008) and to be widely distributed throughout the interstellar medium (ISM) in both the gas and solid phases (Salama 2008). The carbonaceous component of interstellar dust is assumed to be formed in the envelopes around carbon stars by a series of reactions, nucleations and/or aggregations that lead from small carbon chains, via small and medium-sized PAHs, to larger PAHs, aggregates and nanoparticles (Pascoli & Polleux 2000;Contreras & Salama 2013).…”

Section: Introductionmentioning

confidence: 99%

Efficient photochemistry of coronene:water complexes

Noble

Jouvet

Aupetit

et al. 2017

A&A

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The photochemistry of ices with polycyclic aromatic hydrocarbons (PAHs) has been extensively studied, but to date no investigation has been made of PAHs in interaction with low numbers (n < 4) of molecules of water. We performed photochemical matrix isolation studies of coronene:water complexes, probing the argon matrix with FTIR spectroscopy. We find that coronene readily reacts with water upon irradiation with a mercury vapour lamp to produce oxygenated PAH photoproducts, and we postulate a reaction mechanism via a charge transfer Rydberg state. This result suggests that oxygenated PAHs should be widely observed in regions of the ISM with sufficiently high water abundances, for example near the edges of molecular clouds where water molecules begin to form, but before icy layers are observed, that is at A V < 3. In order to explain the low derived observational abundances of oxygenated PAHs, additional destruction routes must be invoked.

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“…Probably the ISM contains thousands of different PAHs in various abundances. Many infrared spectra of mixtures of these compounds fit well with the spectra of the ISM [76,77]. Due to the high similarities of all these compounds between them, it has not been possible up to now to differentiate unambiguously between the systems.…”

Section: Anthracenementioning

confidence: 77%

Organic synthesis applied to space sciences

Guillemin

2011

EPJ Web of Conferences

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Abstract. About 160 molecules have been detected in the interstellar medium, the comae and the atmospheres of planets. The presence of these compounds leads to imagine a chemistry of these media to explain the formation of these species and to predict the possible presence of other ones. Many of them have never been synthesized or isolated in labs and their preparation can be challenging, up to necessitate news reactions or special equipments.

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PAHs in Astronomy - A Review

Cited by 51 publications

References 36 publications

Linear and circular spectropolarimetry of diffuse interstellar bands

Linear and circular spectropolarimetry of diffuse interstellar bands

Efficient photochemistry of coronene:water complexes

Organic synthesis applied to space sciences

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