The mid-infrared spectrum of the carbon star HD 38218 and its possible relation to polycyclic aromatic hydrocarbons

1991 ◽  
Vol 372 ◽  
pp. 281 ◽  
Author(s):  
Richard H., Jr. Buss ◽  
A. G. G. M. Tielens ◽  
Theodore P. Snow
Keyword(s):  
Polycyclic Aromatic Hydrocarbons ◽  
Infrared Spectrum ◽  
Aromatic Hydrocarbons ◽  
Carbon Star ◽  
Mid Infrared ◽  
Polycyclic Aromatic

scholarly journals The spatial extent of polycyclic aromatic hydrocarbons emission in the Herbig star HD 179218

2018 ◽  
Vol 612 ◽  
pp. A15 ◽  
Author(s):  
A. S. Taha ◽  
L. Labadie ◽  
E. Pantin ◽  
A. Matter ◽  
C. Alvarez ◽  
...  
Keyword(s):  
Polycyclic Aromatic Hydrocarbons ◽  
Radiative Transfer ◽  
Aromatic Hydrocarbons ◽  
Central Star ◽  
Spatial Extent ◽  
Continuum Emission ◽  
Mid Infrared ◽  
Spatially Resolved ◽  
Polycyclic Aromatic ◽  
The Continuum

Aim. We investigate, in the mid-infrared, the spatial properties of the polycyclic aromatic hydrocarbons (PAHs) emission in the disk of HD 179218, an intermediate-mass Herbig star at ~300 pc. Methods. We obtained mid-infrared images in the PAH-1, PAH-2 and Si-6 filters centered at 8.6, 11.3, and 12.5 μm, and N-band low-resolution spectra using CanariCam on the 10-m Gran Telescopio Canarias (GTC). We compared the point spread function (PSF) profiles measured in the PAH filters to the profile derived in the Si-6 filter, where the thermal continuum emission dominates. We performed radiative transfer modeling of the spectral energy distribution (SED) and produced synthetic images in the three filters to investigate different spatial scenarios. Results. Our data show that the disk emission is spatially resolved in the PAH-1 and PAH-2 filters, while unresolved in the Si-6 filter. Thanks to very good observing conditions, an average full width at half maximum (FWHM) of 0.232′′, 0.280′′ and 0.293′′ is measured in the three filters, respectively. Gaussian disk fitting and quadratic subtraction of the science and calibrator PSFs suggests a lower-limit characteristic angular diameter of the emission of ~100 mas, or ~30 au. The photometric and spectroscopic results are compatible with previous findings. Our radiative transfer (RT) modeling of the continuum suggests that the resolved emission should result from PAH molecules on the disk atmosphere being UV-excited by the central star. Simple geometrical models of the PAH component compared to the underlying continuum point to a PAH emission uniformly extended out to the physical limits of the disk model. Furthermore, our RT best model of the continuum requires a negative exponent of the surface density power-law, in contrast with earlier modeling pointing to a positive exponent. Conclusions. We have spatially resolved – for the first time to our knowledge – the PAHs emission in the disk of HD 179218 and set constraints on its spatial extent. Based on spatial and spectroscopic considerations as well as on qualitative comparison with IRS 48 and HD 97048, we favor a scenario in which PAHs extend out to large radii across the flared disk surface and are at the same time predominantly in an ionized charge state due to the strong UV radiation field of the 180 L⊙ central star.

scholarly journals Anharmonicity in the mid-infrared spectra of polycyclic aromatic hydrocarbons: molecular beam spectroscopy and calculations

2019 ◽  
Vol 628 ◽  
pp. A130 ◽  
Author(s):  
A. K. Lemmens ◽  
D. B. Rap ◽  
J. M. M. Thunnissen ◽  
C. J. Mackie ◽  
A. Candian ◽  
...  
Keyword(s):  
Polycyclic Aromatic Hydrocarbons ◽  
Infrared Spectra ◽  
Aromatic Hydrocarbons ◽  
Molecular Beam ◽  
Supersonic Jet ◽  
Ir Absorption ◽  
Mid Infrared ◽  
Out Of Plane ◽  
Polycyclic Aromatic ◽  
Combination Bands

Aims. In this work we determine the effects of anharmonicity on the mid-infrared spectra of the linear polycyclic aromatic hydrocarbons (PAHs) naphthalene, anthracene, tetracene and pentacene recorded using the free electron laser FELIX. Methods. Comparison of experimental spectra obtained under supersonic jet conditions with theoretically predicted spectra was used to show if anharmonicity explicitly needs to be taken into account. Results. Anharmonic spectra obtained using second-order vibrational perturbation theory agree on average within 0.5% of the experimental frequencies. Importantly, they confirm the presence of combination bands with appreciable intensity in the 5–6 μm region. These combination bands contain a significant fraction of the IR absorption, which scales linearly with the size of the PAH. Detection and assignment of the combination bands are a preliminary indication of the accuracy of far-IR modes in our anharmonic theoretical spectra. Detailed analysis of the periphery-sensitive CH out-of-plane band of naphthalene reveals that there is still room for improvement of the VPT2 approach. In addition, the implications of our findings for the analysis of the aromatic infrared bands are discussed.

scholarly journals Interstellar polycyclic aromatic hydrocarbons: Spectroscopy, photofragmentation and photoproducts

2019 ◽  
Vol 15 (S350) ◽  
pp. 353-355
Author(s):  
Jordy Bouwman ◽  
Jerry Kamer ◽  
Pablo Castellanos ◽  
Michał Bulak ◽  
Sanjana Panchagnula ◽  
...  
Keyword(s):  
Polycyclic Aromatic Hydrocarbons ◽  
Aromatic Hydrocarbons ◽  
Density Functional ◽  
Ion Trap ◽  
Infrared Emission ◽  
Functional Theory ◽  
Mid Infrared ◽  
Radiation Fields ◽  
Polycyclic Aromatic ◽  
Spectroscopic Signatures

AbstractUbiquitous strong mid-infrared emission bands are observed towards many objects and are attributed to interstellar Polycyclic Aromatic Hydrocarbons (PAHs). PAHs are ionized, or even dissociate, when exposed to strong interstellar radiation fields. By means of ion trap mass spectrometry, light-induced dissociation patterns of PAH cations are measured and the mid-infrared spectroscopic signatures of the parent ion and its dissociation products are characterized. These results are then combined with density functional theory (DFT) calculations to obtain insight into the dissociation characteristics of interstellar PAHs at a molecular level.

scholarly journals Aromatic Infrared Emission in Cirrus Clouds

1989 ◽  
Vol 135 ◽  
pp. 119-128
Author(s):  
J. L. Puget
Keyword(s):  
Polycyclic Aromatic Hydrocarbons ◽  
Energy Distribution ◽  
Aromatic Hydrocarbons ◽  
Thermal Equilibrium ◽  
Molecular Clouds ◽  
Infrared Emission ◽  
Cirrus Clouds ◽  
Mid Infrared ◽  
Spectrophotometric Data ◽  
Polycyclic Aromatic

We discuss the fraction of the infrared cirrus emission radiated out of thermal equilibrium using the IRAS data. Recent spectrophotometric data (Giard et al., 1988a, 1988b) are presented which confirm that aromatic infrared bands account for at least a fraction of their near and mid-infrared cirrus emission as was suspected from indirect arguments. Large variations of the energy distribution among the IRAS bands are shown to be present in molecular clouds. Abundances of polycyclic aromatic hydrocarbons (PAH's) required to account for the emission are discussed.

The Assessment of Contamination and Source of Polycyclic Aromatic Hydrocarbons from the Sediments of the Someş River

2019 ◽  
Vol 64 (1) ◽  
pp. 55-67
Author(s):  
Vlad Pӑnescu ◽  
◽  
Mihaela Cӑtӑlina Herghelegiu ◽  
Sorin Pop ◽  
Mircea Anton ◽  
...  
Keyword(s):  
Polycyclic Aromatic Hydrocarbons ◽  
Aromatic Hydrocarbons ◽  
Polycyclic Aromatic
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