Astronomical observations of the PAH emission bands

Peeters, E.

doi:10.1051/eas/1146002

Cited by 21 publications

(14 citation statements)

References 60 publications

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“…3, 6.2, 7.7, 8.6, and 11.3 μm has been commonly observed in a wide variety of astronomical environments such as the planetary nebulae (NGC 7027), the photodissociation region at the Orion Bar, and the nuclear region of NGC 4536 (Peeters 2011). These bands are attributed to various vibrational modes of aromatic hydrocarbon bonds.…”

Section: Introductionmentioning

confidence: 93%

Mid-infrared spectroscopy of UV irradiated hydrogenated amorphous carbon materials

Gadallah

Mutschke

Jäger

2012

A&A

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Context. Mid-infrared (MIR) bands are characteristic for the short-range and medium-range structure of hydrogenated amorphous carbon (HAC) materials that exist in the interstellar medium (ISM) and are sensitive to processing in the harsh interstellar radiation field. Aims. We study the variability of the MIR features from the spectrum of non-processed to that of UV-processed HAC materials and compare them to spectra of interstellar carbonaceous materials. Methods. Nano-sized HAC materials produced by laser ablation were irradiated by vacuum-UV photons with doses comparable to those relevant for interstellar processing. They were subsequently analyzed by IR spectroscopy. Results. In the MIR range, the spectra of HAC materials show many absorption bands such as the sp 3 aliphatic ≡C-H stretching vibration at 3.03 μm, the sp 3 aliphatic -C-H stretching vibration at 3.4 μm and also the sp 3 aliphatic C-H bending vibration at both 6.85 μm and 7.25 μm. All these are recognizable bands of HAC materials. Other absorption bands such as the sp 2 aromatic =C-H stretching vibration at about 3.3 μm and the sp 2 -C=C stretching vibration close to 6.25 μm are observed. The HAC materials also possess bands which represent the aromatic out-of-plane bending at 11.65, 12.46 and 12.9 μm in addition to the aromatic -C-C-C in-plane bending at 15.87 μm. With UV irradiation, the mass absorption coefficient of the 3.03 μm band completely disappears and that of the aliphatic C-H bands (3.4, 6.85 and 7.25 μm) decreases. This reduction shows that the UV radiation destroys most of the aliphatic C-H bonds inside the HAC structure. On the other hand, the strength of the aromatic 6.2 μm band increases, which is evidence of the partial graphitization within UV-irradiated HAC materials. Because UV irradiation is not uniform, this band agrees well with the C-class PAH toward HD 100764. The C-H out-of-plane vibration bands are strongly affected by UV irradiation. Bands at 11.35, 12.14 and 12.64 μm (solo, duo and trio, respectively), which are found for PAHs of many interstellar spectra were observed partially and were compared to those of non-processed materials, in particular, those at 11.35 μm, which represent the aromatic structures. Conclusions. UV irradiation has a variable effect on both aliphatic and aromatic bands in the MIR region. The aliphatic C-H structure decreases while the aromatic C=C structure, which might lead to the graphitic colonies for PAHs, increases. UV irradiation has revealed solo, duo and trio bands that are relatively consistent with those of the A-and B-class PAHs.

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Section: Introductionmentioning

confidence: 93%

Mid-infrared spectroscopy of UV irradiated hydrogenated amorphous carbon materials

Gadallah

Mutschke

Jäger

2012

A&A

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“…The PAH emission seen in all sample stars can be identified as class C (or BC), depending on the underlying silicate emission (Peeters 2011, and references therein). All our sources follow the trend between the effective temperature of the central star and the central wavelength of the 7-8 μm PAH feature (Sloan et al 2007;Smolders et al 2010).…”

Section: Pahsmentioning

confidence: 99%

“…Bakker et al 1997;Speck et al 1997;Peeters et al 2002;Hony et al 2003;Matsuura et al 2006;Volk et al 2011). Recently, even more complex carbon molecules, namely C 60 and C 70 fullerenes, were detected in the CE of evolved stars (Cami et al 2010;García-Hernández et al 2010, 2011Zhang & Kwok 2011). In some cases, a strong mixed chemistry is seen in the CE of evolved objects (Szczerba et al 2007).…”

Section: Introductionmentioning

confidence: 99%

Carbonaceous molecules in the oxygen-rich circumstellar environment of binary post-AGB stars

Gielen

Cami

Bouwman

et al. 2011

A&A

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Context. The circumstellar environment of evolved stars is generally rich in molecular gas and dust. Typically, the entire environment is either oxygen-rich or carbon-rich, depending on the evolution of the central star. Aims. In this paper we discuss three evolved disc sources with evidence of atypical emission lines in their infrared spectra. The stars were taken from a larger sample of post-AGB binaries for which we have Spitzer infrared spectra, characterised by the presence of a stable oxygen-rich circumbinary disc. Our previous studies have shown that the infrared spectra of post-AGB disc sources are dominated by silicate dust emission, often with an extremely high crystallinity fraction. However, the three sources described here are selected because they show a peculiar molecular chemistry. Methods. Using Spitzer infrared spectroscopy, we study in detail the peculiar mineralogy of the three sample stars. Using the observed emission features, we identify the different observed dust, molecular and gas species. Results. The infrared spectra show emission features due to various oxygen-rich dust components, as well as CO 2 gas. All three sources show the strong infrared bands generally ascribed to polycyclic aromatic hydrocarbons. Furthermore, two sample sources show C 60 fullerene bands. Conclusions. Even though the majority of post-AGB disc sources are dominated by silicate dust in their circumstellar environment, we do find evidence that, for some sources at least, additional processing must occur to explain the presence of large carbonaceous molecules. There is evidence that some of these sources are still oxygen-rich, which makes the detection of these molecules even more surprising.

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“…Together the UIB, DIB, UV bump, and 3.4 µm feature constitute a significant part (> 30%) of the available cosmic carbon budget. Herbig (1995), Sarre et al (2006) (and references therein); (3) Butchart et al (1986), M cFadzean et al (1989, Adamson et al (1990), Pendleton et al (1994, Sandford et al (1995), Chiar & Pendleton, 2008;(4) Tielens (2011), Peeters, (2011), Cami et al (2011), Draine (2011), Peeters, (2011.…”

Section: The Diffuse Ism and Its Organic Constituentsmentioning

confidence: 99%

The Diffuse Interstellar Bands: an Elderly Astro-Puzzle Rejuvenated

Cox

2011

Proc. IAU

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Abstract. The interstellar medium constitutes a physically and chemically complex component of galaxies and is important in the cycle of matter and the evolution of stars. From various spectroscopic clues we now know that the interstellar medium is rich in organic compounds. However, identifying the exact nature of all these components remains a challenge. In particular the identification of the so-called diffuse band carriers has been alluding astronomers for almost a century.In recent decades, observational, experimental and theoretical advances have rapidly lead to renewed interest in the diffuse interstellar bands (DIBs). This has been instigated partly by their perceived relation to the infrared aromatic emission bands, the UV extinction bump and far-UV rise, and the growing number of (small) organic molecules identified in space.This chapter gives an overview of the observational properties and behaviour of the DIBs, and their presence throughout the Universe. I will highlight recent progress in identifying their carriers and discuss their potential as tracers and probes of (extra)-Galactic ISM conditions.

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Astronomical observations of the PAH emission bands

Cited by 21 publications

References 60 publications

Mid-infrared spectroscopy of UV irradiated hydrogenated amorphous carbon materials

Mid-infrared spectroscopy of UV irradiated hydrogenated amorphous carbon materials

Carbonaceous molecules in the oxygen-rich circumstellar environment of binary post-AGB stars

The Diffuse Interstellar Bands: an Elderly Astro-Puzzle Rejuvenated

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