Mid‐Infrared Spectra of Polycyclic Aromatic Hydrocarbon Emission in Herbig Ae/Be Stars

Sloan, G. C.; Keller, L. D.; Forrest, W. J.; Leibensperger, E. M.; Sargent, B.; Li, A.; Najita, J.; Watson, D. M.; Brandl, Bernhard R.; Chen, C. H.; Green, J. D.; Kemper, F.; Herter, T.; D’Alessio, Paola; Morris, P. W.; Barry, D. J.; Hall, Peter; Myers, Philip C.; Houck, J. R.

doi:10.1086/444371

Cited by 103 publications

(122 citation statements)

References 44 publications

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“…In observed spectra of different lines of sight of the interstellar medium, sp 3 aliphatic hydrocarbons can be detected at 3.4, 6.85 and 7.25 μm, whereas sp 2 aromatic hydrocarbons can be observed at 3.28 μm and 6.2 μm of =CH and C=C stretching modes, respectively, toward the galactic center (Chiar et al 2000). For the 6.2 μm band, the astronomical observations (Sloan et al 2005(Sloan et al , 2007 have shown that there are three band positions corresponding to A, B and C-class PAHs. In addition to the unidentified bands in these observations, several out-of-plane PAH-bands such as 11.3, 12.0, and 12.7 μm have been observed.…”

Section: Astronomical Implicationsmentioning

confidence: 84%

“…This means that there is a transformation from aliphatic to aromatic structures resulting in larger aromatic units. In the range of 10-15 μm, the spectra have revealed emission features at 11.2, 12.7, 13.5, and 14.2 μm (Hony et al 2001;Sloan et al 2005) in different astrophysical environments. They are caused by CH out-of-plane bending modes of PAHs.…”

Section: Introductionmentioning

confidence: 99%

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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: Astronomical Implicationsmentioning

confidence: 84%

Section: Introductionmentioning

confidence: 99%

Mid-infrared spectroscopy of UV irradiated hydrogenated amorphous carbon materials

Gadallah

Mutschke

Jäger

2012

A&A

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“…Jura et al (2006) also report on the detection of class-C PAH features in a circumstellar disc around the oxygen-rich K-giant HD 233517. Two young objects, the T Tauri star SU Aur (Furlan et al 2006) and the Herbig Ae/Be source HD 135344 (Sloan et al 2005), also show PAH spectra of class C, although in HD 135344 the PAH features seem to be somewhat more in between B and C. This source is also slightly hotter than other class C sources. A comparison of the PAH features in all these sources is given by Sloan et al (2007).…”

Section: Pah Featuresmentioning

confidence: 91%

Analysis of the infrared spectra of the peculiar post-AGB stars EP Lyrae and HD 52961

Gielen¹,

Winckel²,

Matsuura

et al. 2009

A&A

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Aims. We aim to study in detail the peculiar mineralogy and structure of the circumstellar environment of two binary post-AGB stars, EP Lyr and HD 52961. Both stars were selected from a larger sample of evolved disc sources observed with Spitzer and show unique solid-state and gas features in their infrared spectra. Moreover, they show a very small infrared excess in comparison with the other sample stars. Methods. The different dust and gas species are identified on the basis of high-resolution Spitzer-IRS spectra. We fit the full spectrum to constrain grain sizes and temperature distributions in the discs. This, combined with our broad-band spectral energy distribution and interferometric measurements, allows us to study the physical structure of the disc, using a self-consistent 2D radiative-transfer disc model. Results. We find that both stars have strong emission features due to CO 2 gas, dominated by 12 C 16 O 2 , but with clear 13 C 16 O 2 and even 16 O 12 C 18 O isotopic signatures. Crystalline silicates are apparent in both sources but proved very hard to model. EP Lyr also shows evidence of mixed chemistry, with emission features of the rare class-C PAHs. Whether these PAHs reside in the oxygen-rich disc or in a carbon-rich outflow is still unclear. With the strongly processed silicates, the mixed chemistry and the low 12 C/ 13 C ratio, EP Lyr resembles some silicate J-type stars, although the depleted photosphere makes nucleosynthetic signatures difficult to probe. We find that the disc environment of both sources is, to a first approximation, well modelled with a passive disc, but additional physics such as grain settling, radial dust distributions, and an outflow component must be included to explain the details of the observed spectral energy distributions in both stars.

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“…In contrast, the spectra reveal no evidence for emission from polycyclic aromatic hydrocarbons. These (carbon-rich) molecular compounds are found in the infrared spectra of the interstellar medium (Draine, 2003), some circumstellar environments (Sloan et al, 2005), and in comets (Bockelée-Morvan et al, 1995), with strong features near 6, 8, and 11 µm. Hence, the circumstellar dust at white dwarfs appears relatively carbon-deficient and rocky (Jura et al, 2009a), and likely similar to the material of the inner Solar System.…”

Section: Infrared Spectra Of Disksmentioning

confidence: 98%

Circumstellar debris and pollution at white dwarf stars

Farihi

2016

New Astronomy Reviews

300

265

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Circumstellar disks of planetary debris are now known or suspected to closely orbit hundreds of white dwarf stars. To date, both data and theory support disks that are entirely contained within the preceding giant stellar radii, and hence must have been produced during the white dwarf phase. This picture is strengthened by the signature of material falling onto the pristine stellar surfaces; disks are always detected together with atmospheric heavy elements. The physical link between this debris and the white dwarf host abundances enables unique insight into the bulk chemistry of extrasolar planetary systems via their remnants. This review summarizes the body of evidence supporting dynamically active planetary systems at a large fraction of all white dwarfs, the remnants of first generation, main-sequence planetary systems, and hence provide insight into initial conditions as well as long-term dynamics and evolution.

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Mid‐Infrared Spectra of Polycyclic Aromatic Hydrocarbon Emission in Herbig Ae/Be Stars

Cited by 103 publications

References 44 publications

Mid-infrared spectroscopy of UV irradiated hydrogenated amorphous carbon materials

Mid-infrared spectroscopy of UV irradiated hydrogenated amorphous carbon materials

Analysis of the infrared spectra of the peculiar post-AGB stars EP Lyrae and HD 52961

Circumstellar debris and pollution at white dwarf stars

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