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B T Draine - One of the best experts on this subject based on the ideXlab platform.
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emission from Very Small Grains and pah molecules in monte carlo radiation transfer codes application to the edge on disk of gomez s hamburger
The Astrophysical Journal, 2008Co-Authors: Kenneth Wood, Barbara A Whitney, Thomas Robitaille, B T DraineAbstract:We have modeled optical to far-infrared images, photometry, and spectroscopy of the object known as Gomez's Hamburger. We reproduce the images and spectrum with an edge-on disk of mass 0.3 M☉ and radius 1600 AU, surrounding an A0 III star at a distance of 280 pc. Our mass estimate is in excellent agreement with recent CO observations. However, our distance determination is more than an order of magnitude Smaller than previous analyses, which inaccurately interpreted the optical spectrum. To accurately model the infrared spectrum we have extended our Monte Carlo radiation transfer codes to include emission from polycyclic aromatic hydrocarbon (PAH) molecules and Very Small Grains (VSG). We do this using precomputed PAH/VSG emissivity files for a wide range of values of the mean intensity of the exciting radiation field. When Monte Carlo energy packets are absorbed by PAHs/VSGs, we reprocess them to other wavelengths by sampling from the emissivity files, thus simulating the absorption and reemission process without reproducing lengthy computations of statistical equilibrium, excitation, and de-excitation in the complex many-level molecules. Using emissivity lookup tables in our Monte Carlo codes gives us the flexibility to use the latest grain physics calculations of PAH/VSG emissivity and opacity that are being continually updated in the light of higher resolution infrared spectra. We find our approach gives a good representation of the observed PAH spectrum from the disk of Gomez's Hamburger. Our models also indicate that the PAHs/VSGs in the disk have a larger scale height than larger radiative equilibrium Grains, providing evidence for dust coagulation and settling to the midplane.
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infrared emission from interstellar dust i stochastic heating of Small Grains
The Astrophysical Journal, 2001Co-Authors: B T DraineAbstract:We present a method for calculating the infrared emission from a population of dust Grains heated by starlight, including Very Small Grains for which stochastic heating by starlight photons results in high- temperature transients. Because state-to-state transition rates are generally unavailable for complex mol ecules, we consider model polycyclic aromatic hydrocarbon (PAH), graphitic, and silicate Grains with realistic vibrational mode spectra and realistic radiative properties. The vibrational density of states is used in a statistical-mechanical description of the emission process. Unlike previous treatments, our approach fully incorporates multiphoton heating effects, important for large Grains or strong radiation fields. We discuss how the "temperature" of the grain is related to its vibrational energy. By comparing with an "exact" statistical calculation of the emission process, we determine the conditions under which the "thermal" and the "continuous cooling" approximations can be used to calculate the emission spec trum. We present results for the infrared emission spectra of PAH Grains of various sizes heated by star light. We show how the relative strengths of the 6.2, 7.7, and 11.3 μm features depend on grain size, starlight spectrum and intensity, and grain charging conditions. We show results for Grains in the "cold neutral medium" and "warm ionized medium" and representative conditions in photodissociation regions. Our model results are compared to observed ratios of emission features for the Milky Way and other galaxies and for the M17 and NGC 7023 photodissociation regions.
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on ultraSmall silicate Grains in the diffuse interstellar medium
The Astrophysical Journal, 2001Co-Authors: B T DraineAbstract:The abundance of both amorphous and crystalline silicates in Very Small Grains is limited by the fact that the 10 ?m silicate emission feature is not detected in the diffuse interstellar medium (ISM). On the basis of the observed IR emission spectrum for the diffuse ISM, the observed ultraviolet extinction curve, and the 10 ?m silicate absorption profile, we obtain upper limits on the abundances of ultraSmall (a 15 ?) amorphous and crystalline silicate Grains. Contrary to previous work, as much as ~10% of interstellar Si could be in a 15 ? silicate Grains without violating observational constraints. Not more than ~5% of the Si can be in crystalline silicates (of any size).
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dust grain size distributions and extinction in the milky way large magellanic cloud and Small magellanic cloud
The Astrophysical Journal, 2001Co-Authors: J C Weingartner, B T DraineAbstract:We construct size distributions for carbonaceous and silicate grain populations in different regions of the Milky Way, LMC, and SMC. The size distributions include sufficient Very Small carbonaceous Grains (including polycyclic aromatic hydrocarbon molecules) to account for the observed infrared and microwave emission from the diffuse interstellar medium. Our distributions reproduce the observed extinction of starlight, which varies depending on the interstellar environment through which the light travels. As shown by Cardelli, Clayton, and Mathis in 1989, these variations can be roughly parameterized by the ratio of visual extinction to reddening, RV. We adopt a fairly simple functional form for the size distribution, characterized by several parameters. We tabulate these parameters for various combinations of values for RV and bC, the C abundance in Very Small Grains. We also find size distributions for the line of sight to HD 210121 and for sight lines in the LMC and SMC. For several size distributions, we evaluate the albedo and scattering asymmetry parameter and present model extinction curves extending beyond the Lyman limit.
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on ultraSmall silicate Grains in the diffuse interstellar medium
arXiv: Astrophysics, 2000Co-Authors: B T DraineAbstract:The abundance of both amorphous and crystalline silicates in Very Small Grains is limited by the fact that the 10 micron silicate emission feature is not detected in the diffuse ISM. On the basis of the observed IR emission spectrum for the diffuse ISM, the observed ultraviolet extinction curve, and the 10 micron silicate absorption profile, we obtain upper limits on the abundances of ultraSmall (a < 15 Angstrom) amorphous and crystalline silicate Grains. Contrary to previous work, as much as ~20% of interstellar Si could be in a < 15 Angstrom silicate Grains without violating observational constraints. Not more than ~5% of the Si can be in crystalline silicates (of any size).
C Joblin - One of the best experts on this subject based on the ideXlab platform.
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the infrared signatures of Very Small Grains in the universe seen by jwst
arXiv: Astrophysics of Galaxies, 2015Co-Authors: Paolo Pilleri, O Berne, C JoblinAbstract:The near- and mid-IR spectrum of many astronomical objects is dominated by emission bands due to UV-excited polycyclic aromatic hydrocarbons (PAH) and evaporating Very Small Grains (eVSG). Previous studies with the ISO, Spitzer and AKARI space telescopes have shown that the spectral variations of these features are directly related to the local physical conditions that induce a photo-chemical evolution of the band carriers. Because of the limited sensitivity and spatial resolution, these studies have focused mainly on galactic star-forming regions. We discuss how the advent of JWST will allow to extend these studies to previously unresolved sources such as near-by galaxies, and how the analysis of the infrared signatures of PAHs and eVSGs can be used to determine their physical conditions and chemical composition.
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mixed aliphatic and aromatic composition of evaporating Very Small Grains in ngc 7023 revealed by the 3 4 3 3 μm ratio
Astronomy and Astrophysics, 2015Co-Authors: C Joblin, F. Boulanger, P Pilleri, Takashi OnakaAbstract:Context. A chemical scenario was proposed for photon-dominated regions (PDRs) according to which UV photons from nearby stars lead to the evaporation of Very Small Grains (VSGs) and the production of gas-phase polycyclic aromatic hydrocarbons (PAHs). Aims. Our goal is to achieve better insight into the composition and evolution of evaporating Very Small Grains (eVSGs) and PAHs through analyzing the infrared (IR) aliphatic and aromatic emission bands. Methods. We combined spectro-imagery in the near- and mid-IR to study the spatial evolution of the emission bands in the prototypical PDR NGC 7023. We used near-IR spectra obtained with the IRC instrument onboard AKARI to trace the evolution of the 3.3 m and 3.4 m bands, which are associated with aromatic and aliphatic C H bonds on PAHs. The spectral fitting involved an additional broad feature centered at 3.45 m that is often referred to as the plateau. Mid-IR observations obtained with the IRS instrument onboard the Spitzer Space Telescope were used to distinguish the signatures of eVSGs and neutral and cationic PAHs. We correlated the spatial evolution of all these bands with the intensity of the UV field given in units of the Habing field G0 to explore how their carriers are processed. Results. The intensity of the 3.45 m plateau shows an excellent correlation with that of the 3.3 m aromatic band (correlation coe cient R = 0:95) and a relatively poor correlation with the aliphatic 3.4 m band (R = 0:77). This indicates that the 3.45 m feature is dominated by the emission from aromatic bonds. We show that the ratio of the 3.4 m and 3.3 m band intensity (I3:4=I3:3) decreases by a factor of 4 at the PDR interface from the more UV-shielded layers (G0 150;I3:4=I3:3 = 0:13) to the more exposed layers (G0 > 1 10 4 ;I3:4=I3:3 = 0:03). The intensity of the 3.3 m band relative to the total neutral PAH intensity shows an overall increase with G0, associated with an increase of both the hardness of the UV field and the H abundance. In contrast, the intensity of the 3.4 m band relative to the total neutral PAH intensity decreases with G0, showing that their carriers are actively destroyed by UV irradiation and are not e ciently regenerated. The transition region between the aliphatic and aromatic material is found to correspond spatially with the transition zone between neutral PAHs and eVSGs. Conclusions. We conclude that the photo-processing of eVSGs leads to the production of PAHs with attached aliphatic sidegroups that are revealed by the 3.4 m emission band. Our analysis provides evidence for the presence of Very Small Grains of mixed aromatic and aliphatic composition in PDRs.
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evaporating Very Small Grains as tracers of the uv radiation field in photo dissociation regions
arXiv: Astrophysics of Galaxies, 2012Co-Authors: P Pilleri, O Berne, C Joblin, J. MontillaudAbstract:Context. In photo-dissociation regions (PDRs), Polycyclic Aromatic Hydrocarbons (PAHs) could be produced by evaporation of Very Small Grains (VSGs) by the impinging UV radiation field from a nearby star. Aims. We investigate quantitatively the transition zone between evaporating Very Small Grains (eVSGs) and PAHs in several PDRs. Methods. We study the relative contribution of PAHs and eVSGs to the mid-IR emission in a wide range of excitation conditions. We fit the observed mid-IR emission of PDRs by using a set of template band emission spectra of PAHs, eVSGs and gas lines. The fitting tool PAHTAT (PAH Toulouse Astronomical Templates) is made available to the community as an IDL routine. From the results of the fit, we derive the fraction of carbon f_eVSG locked in eVSGs and compare it to the intensity of the local UV radiation field. Results. We show a clear decrease of f_eVSG with increasing intensity of the local UV radiation field, which supports the scenario of photo-destruction of eVSGs. Conversely, this dependence can be used to quantify the intensity of the UV radiation field for different PDRs, including non resolved ones. Conclusions. PAHTAT can be used to trace the intensity of the local UV radiation field in regions where eVSGs evaporate, which correspond to relatively dense (nH = [100, 10^5 ] cm-3) and UV irradiated PDRs (G0 = [100, 5x10^4]) where H2 emits in rotational lines.
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PAH-related Very Small Grains in photodissociation regions: implications from molecular simulations
EAS Publications Series, 2011Co-Authors: Mathias Rapacioli, O Berne, C Joblin, Fernand Spiegelman, Baptiste Joalland, Aude Simon, André Mirtschink, J. Montillaud, D. TalbiAbstract:The analysis of mid-IR emission suggests that a population of PAH-related Very Small Grains containing a few hundreds of atoms are present in the deep regions of molecular clouds, although no specific species has been identified yet. In this review, we discuss several candidates for these Grains: neutral and ionised PAH clusters and complexes of PAHs with Si atoms. The theoretical modelling of the properties of such molecular complexes or nanoGrains is a challenging task. We first present an overview of quantum chemistry derived models which can be efficiently used on-the-fly in extensive sampling of the potential energy surfaces, as required by structural optimization, classical molecular dynamics or Monte Carlo algorithms. From the simulations, various observables can be determined, such as the binding energies, finite temperature IR spectra, nucleation and evaporation rates. We discuss the relevance of those candidates in the molecular clouds photodissociation regions and propose constrains and perspectives for the nature and size of those Very Small Grains.
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photodissociation of fex c24h12 y complexes in the pirenea setup iron polycyclic aromatic hydrocarbon clusters as candidates for Very Small interstellar Grains
Journal of Physical Chemistry A, 2009Co-Authors: Aude Simon, C JoblinAbstract:Astronomical observations suggest that polycyclic aromatic hydrocarbons (PAHs) that emit at the surface of molecular clouds in the interstellar medium are locally produced by photodestruction of Very Small Grains (VSGs). In this paper, we investigate [Fex(PAH)y]+ clusters as candidates for these VSGs. [FeC24H12]+ and [Fex(C24H12)2]+ (x = 1-3) complexes were formed by laser ablation of a solid target in the PIRENEA setup, a cold ion trap dedicated to astrochemistry. Their photodissociation was studied under continuous visible irradiation. Photodissociation pathways are identified and characteristic time scales for photostability are provided. [Fex(C24H12)2]+ (x = 1-3) complexes sequentially photodissociate by losing iron atoms and coronene units under laboratory irradiation conditions with C24H12+ as the Smallest photofragment. The study of the dissociation kinetics gives interesting insights into the structures of the complexes. The dissociation rate is found to increase with the complex size. Density functional theory (DFT) and time-dependent DFT calculations show that the increase of the number of Fe atoms leads to an increased stability of the complex but also to an increased heating rate in the experimental conditions, due to the presence of strong electronic excitations in the visible. The modeling of the dissociation kinetics of the Smallest complex [FeC24H12]+ by using a kinetic Monte Carlo code allows derivation of the dissociation parameters and the internal energy for this complex, showing in particular that it could dissociate under interstellar irradiation conditions. First insights into the dissociation of larger complexes in these conditions are also given.
P Pilleri - One of the best experts on this subject based on the ideXlab platform.
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mixed aliphatic and aromatic composition of evaporating Very Small Grains in ngc 7023 revealed by the 3 4 3 3 μm ratio
Astronomy and Astrophysics, 2015Co-Authors: C Joblin, F. Boulanger, P Pilleri, Takashi OnakaAbstract:Context. A chemical scenario was proposed for photon-dominated regions (PDRs) according to which UV photons from nearby stars lead to the evaporation of Very Small Grains (VSGs) and the production of gas-phase polycyclic aromatic hydrocarbons (PAHs). Aims. Our goal is to achieve better insight into the composition and evolution of evaporating Very Small Grains (eVSGs) and PAHs through analyzing the infrared (IR) aliphatic and aromatic emission bands. Methods. We combined spectro-imagery in the near- and mid-IR to study the spatial evolution of the emission bands in the prototypical PDR NGC 7023. We used near-IR spectra obtained with the IRC instrument onboard AKARI to trace the evolution of the 3.3 m and 3.4 m bands, which are associated with aromatic and aliphatic C H bonds on PAHs. The spectral fitting involved an additional broad feature centered at 3.45 m that is often referred to as the plateau. Mid-IR observations obtained with the IRS instrument onboard the Spitzer Space Telescope were used to distinguish the signatures of eVSGs and neutral and cationic PAHs. We correlated the spatial evolution of all these bands with the intensity of the UV field given in units of the Habing field G0 to explore how their carriers are processed. Results. The intensity of the 3.45 m plateau shows an excellent correlation with that of the 3.3 m aromatic band (correlation coe cient R = 0:95) and a relatively poor correlation with the aliphatic 3.4 m band (R = 0:77). This indicates that the 3.45 m feature is dominated by the emission from aromatic bonds. We show that the ratio of the 3.4 m and 3.3 m band intensity (I3:4=I3:3) decreases by a factor of 4 at the PDR interface from the more UV-shielded layers (G0 150;I3:4=I3:3 = 0:13) to the more exposed layers (G0 > 1 10 4 ;I3:4=I3:3 = 0:03). The intensity of the 3.3 m band relative to the total neutral PAH intensity shows an overall increase with G0, associated with an increase of both the hardness of the UV field and the H abundance. In contrast, the intensity of the 3.4 m band relative to the total neutral PAH intensity decreases with G0, showing that their carriers are actively destroyed by UV irradiation and are not e ciently regenerated. The transition region between the aliphatic and aromatic material is found to correspond spatially with the transition zone between neutral PAHs and eVSGs. Conclusions. We conclude that the photo-processing of eVSGs leads to the production of PAHs with attached aliphatic sidegroups that are revealed by the 3.4 m emission band. Our analysis provides evidence for the presence of Very Small Grains of mixed aromatic and aliphatic composition in PDRs.
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mixed aliphatic and aromatic composition of evaporating Very Small Grains in ngc 7023 revealed by the 3 4 3 3 mu m ratio
arXiv: Astrophysics of Galaxies, 2015Co-Authors: P Pilleri, F. Boulanger, C Joblin, Takashi OnakaAbstract:In photon-dominated regions (PDRs), UV photons from nearby stars lead to the evaporation of Very Small Grains (VSGs) and the production of gas-phase polycyclic aromatic hydrocarbons (PAHs). Our goal is to achieve better insight into the composition and evolution of evaporating Very Small Grains (eVSGs) and PAHs through analyzing the infrared (IR) aliphatic and aromatic emission bands. We combined spectro-imagery in the near- and mid-IR to study the spatial evolution of the emission bands in the prototypical PDR NGC 7023. We used near-IR spectra obtained with AKARI to trace the evolution of the 3.3$\mu$m and 3.4$\mu$m bands, which are associated with aromatic and aliphatic C-H bonds on PAHs. The spectral fitting involves an additional broad feature centred at 3.45$\mu$m. Mid-IR observations obtained with Spitzer are used to discriminate the signatures of eVSGs, neutral and cationic PAHs. We correlated the spatial evolution of all these bands with the intensity of the UV field to explore the processing of their carriers. The intensity of the 3.45$\mu$m plateau shows an excellent correlation with that of the 3.3$\mu$m aromatic band (correlation coefficient R = 0.95), indicating that the plateau is dominated by the emission from aromatic bonds. The ratio of the 3.4$\mu$m and 3.3$\mu$m band intensity ($I_{3.4}/I_{3.3}$) decreases by a factor of 4 at the PDR interface from the more UV-shielded to the more exposed layers. The transition region between the aliphatic and aromatic material is found to correspond spatially with the transition zone between neutral PAHs and eVSGs. We conclude that the photo-processing of eVSGs leads to the production of PAHs with attached aliphatic sidegroups that are revealed by the 3.4$\mu$m emission band. Our analysis provides evidence for the presence of Very Small Grains of mixed aromatic and aliphatic composition in PDRs.
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the mixed aliphatic aromatic composition of evaporating Very Small Grains in ngc 7023 viewed by the 3 4 3 3 m ratio
arXiv: Astrophysics of Galaxies, 2015Co-Authors: P Pilleri, F. Boulanger, C Joblin, Takashi OnakaAbstract:Context. In photon-dominated regions (PDRs), a chemical scenario was proposed in which UV photons from nearby stars lead to the evaporation of Very Small Grains (VSGs) and the production of gas-phase polycyclic aromatic hydrocarbons (PAHs). Aims. Our goal is to get further insights into the composition and evolution of evaporating Very Small Grains (eVSGs) and PAHs through the analysis of the infrared (IR) aliphatic and aromatic emission bands. Methods. We combine spectro-imagery in the near- and mid-IR to study the spatial evolution of the emission bands in the prototypical PDR NGC 7023. We use near-IR spectra obtained with the IRC instrument onboard AKARI to trace the evolution of the 3.3 m and 3.4 m bands that are associated with aromatic and aliphatic C H bonds on PAHs, respectively. The spectral fitting involves an additional broad feature centred at 3.45 m often referred to as the plateau. Mid-IR observations obtained with the IRS instrument onboard the Spitzer Space Telescope are used to discriminate the signatures of eVSGs, neutral and cationic PAHs. We correlate the spatial evolution of all these bands with the intensity of the UV field given in units of the Habing field G0 to explore the processing of their carriers. Results. The intensity of the 3.45 m plateau shows an excellent correlation with that of the 3.3 m aromatic band (correlation coefficient R = 0.95) and a relatively poor correction with the aliphatic 3.4 m band (R=0.77). This indicates that the 3.45 m feature is dominated by the emission from aromatic bonds. We show that the ratio of the 3.4 m and 3.3 m band intensity (I3:4=I3:3) decreases by a factor of 4 at the PDR interface from the more UV-shielded layers (G0 150;I3:4=I3:3 = 0:13) to the more exposed layers (G0 > 1 10 4 ;I3:4=I3:3 = 0:03). The intensity of the 3.3 m band relative to the total neutral PAH intensity shows an overall increase with G0, associated to both an increase of the hardness of the UV field and of the H abundance. On the contrary, the intensity of the 3.4 m band relative to the total neutral PAH intensity decreases with G0, showing that their carriers are actively destroyed by UV irradiation and not e ciently regenerated. The transition region between the aliphatic and aromatic material is found to correspond spatially with the transition zone between neutral PAHs and eVSGs. Conclusions. We conclude that the photo-processing of eVSGs leads to the production of PAHs with attached aliphatic sidegroups that are revealed by the 3.4 m emission band. Our analysis provides evidence for the presence of Very Small Grains of mixed aromatic/aliphatic composition in PDRs.
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evaporating Very Small Grains as tracers of the uv radiation field in photo dissociation regions
arXiv: Astrophysics of Galaxies, 2012Co-Authors: P Pilleri, O Berne, C Joblin, J. MontillaudAbstract:Context. In photo-dissociation regions (PDRs), Polycyclic Aromatic Hydrocarbons (PAHs) could be produced by evaporation of Very Small Grains (VSGs) by the impinging UV radiation field from a nearby star. Aims. We investigate quantitatively the transition zone between evaporating Very Small Grains (eVSGs) and PAHs in several PDRs. Methods. We study the relative contribution of PAHs and eVSGs to the mid-IR emission in a wide range of excitation conditions. We fit the observed mid-IR emission of PDRs by using a set of template band emission spectra of PAHs, eVSGs and gas lines. The fitting tool PAHTAT (PAH Toulouse Astronomical Templates) is made available to the community as an IDL routine. From the results of the fit, we derive the fraction of carbon f_eVSG locked in eVSGs and compare it to the intensity of the local UV radiation field. Results. We show a clear decrease of f_eVSG with increasing intensity of the local UV radiation field, which supports the scenario of photo-destruction of eVSGs. Conversely, this dependence can be used to quantify the intensity of the UV radiation field for different PDRs, including non resolved ones. Conclusions. PAHTAT can be used to trace the intensity of the local UV radiation field in regions where eVSGs evaporate, which correspond to relatively dense (nH = [100, 10^5 ] cm-3) and UV irradiated PDRs (G0 = [100, 5x10^4]) where H2 emits in rotational lines.
O Berne - One of the best experts on this subject based on the ideXlab platform.
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the infrared signatures of Very Small Grains in the universe seen by jwst
arXiv: Astrophysics of Galaxies, 2015Co-Authors: Paolo Pilleri, O Berne, C JoblinAbstract:The near- and mid-IR spectrum of many astronomical objects is dominated by emission bands due to UV-excited polycyclic aromatic hydrocarbons (PAH) and evaporating Very Small Grains (eVSG). Previous studies with the ISO, Spitzer and AKARI space telescopes have shown that the spectral variations of these features are directly related to the local physical conditions that induce a photo-chemical evolution of the band carriers. Because of the limited sensitivity and spatial resolution, these studies have focused mainly on galactic star-forming regions. We discuss how the advent of JWST will allow to extend these studies to previously unresolved sources such as near-by galaxies, and how the analysis of the infrared signatures of PAHs and eVSGs can be used to determine their physical conditions and chemical composition.
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evaporating Very Small Grains as tracers of the uv radiation field in photo dissociation regions
arXiv: Astrophysics of Galaxies, 2012Co-Authors: P Pilleri, O Berne, C Joblin, J. MontillaudAbstract:Context. In photo-dissociation regions (PDRs), Polycyclic Aromatic Hydrocarbons (PAHs) could be produced by evaporation of Very Small Grains (VSGs) by the impinging UV radiation field from a nearby star. Aims. We investigate quantitatively the transition zone between evaporating Very Small Grains (eVSGs) and PAHs in several PDRs. Methods. We study the relative contribution of PAHs and eVSGs to the mid-IR emission in a wide range of excitation conditions. We fit the observed mid-IR emission of PDRs by using a set of template band emission spectra of PAHs, eVSGs and gas lines. The fitting tool PAHTAT (PAH Toulouse Astronomical Templates) is made available to the community as an IDL routine. From the results of the fit, we derive the fraction of carbon f_eVSG locked in eVSGs and compare it to the intensity of the local UV radiation field. Results. We show a clear decrease of f_eVSG with increasing intensity of the local UV radiation field, which supports the scenario of photo-destruction of eVSGs. Conversely, this dependence can be used to quantify the intensity of the UV radiation field for different PDRs, including non resolved ones. Conclusions. PAHTAT can be used to trace the intensity of the local UV radiation field in regions where eVSGs evaporate, which correspond to relatively dense (nH = [100, 10^5 ] cm-3) and UV irradiated PDRs (G0 = [100, 5x10^4]) where H2 emits in rotational lines.
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coupled blind signal separation and spectroscopic database fitting of the mid infrared pah features
Astronomy and Astrophysics, 2011Co-Authors: O Berne, Morris Rosenberg, C Boersma, L J Allamandola, A G G M TielensAbstract:Context. The aromatic infrared bands (AIBs) observed in the mid infrared spectrum of galactic and extragalactic sources are attributed to polycyclic aromatic hydrocarbons (PAHs). Recently, two new approaches have been developed to analyze the variations of AIBs in terms of chemical evolution of PAH species: blind signal separation (BSS) and the NASA Ames PAH IR Spectroscopic Database fitting tool. Aims. We aim to study AIBs in a photo-dissociation region (PDR) since in these regions, as the radiation environment changes, the evolution of AIBs are observed. Methods. We observe the NGC 7023-north west (NW) PDR in the mid-infrared (10–19.5 μm) using the InfraRed Spectrometer (IRS), on board Spitzer, in the high-resolution, short wavelength mode. Clear variations are observed in the spectra, most notably the ratio of the 11.0 to 11.2 μm bands, the peak position of the 11.2 and 12.0 μm bands, and the degree of asymmetry of the 11.2 μm band. The observed variations appear to change as a function of position within the PDR. We aim to explain these variations by a change in the abundances of the emitting components of the PDR. A blind signal separation (BSS) method, i.e. a Non-Negative Matrix Factorization algorithm is applied to separate the observed spectrum into components. Using the NASA Ames PAH IR Spectroscopic Database, these extracted signals are fit. The observed signals alone were also fit using the database and these components are compared to the BSS components. Results. Three component signals were extracted from the observation using BSS. We attribute the three signals to ionized PAHs, neutral PAHs, and Very Small Grains (VSGs). The fit of the BSS extracted spectra with the PAH database further confirms the attribution to PAH + and PAH 0 and provides confidence in both methods for producing reliable results. Conclusions. The 11.0 μm feature is attributed to PAH + while the 11.2 μm band is attributed to PAH 0 . The VSG signal shows a characteristically asymmetric broad feature at 11.3 μm with an extended red wing. By combining the NASA Ames PAH IR Spectroscopic Database fit with the BSS method, the independent results of each method can be confirmed and some limitations of each method are overcome.
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coupled blind signal separation and spectroscopic database fitting of the mid infrared pah features
arXiv: Astrophysics of Galaxies, 2011Co-Authors: O Berne, Morris Rosenberg, C Boersma, L J Allamandola, A G G M TielensAbstract:The aromatic infrared bands (AIBs) observed in the mid infrared spectrum are attributed to Polycyclic Aromatic Hydrocarbons (PAHs). We observe the NGC 7023-North West (NW) PDR in the mid-infrared (10 - 19.5 micron) using the Infrared Spectrometer (IRS), on board Spitzer. Clear variations are observed in the spectra, most notably the ratio of the 11.0 to 11.2 micron bands, the peak position of the 11.2 and 12.0 micron bands, and the degree of asymmetry of the 11.2 micron band. The observed variations appear to change as a function of position within the PDR. We aim to explain these variations by a change in the abundances of the emitting components of the PDR. A Blind Signal Separation (BSS) method, i.e. a Non-Negative Matrix Factorization algorithm is applied to separate the observed spectrum into components. Using the NASA Ames PAH IR Spectroscopic Database, these extracted signals are fit. The observed signals alone were also fit using the database and these components are compared to the BSS components. Three component signals were extracted from the observation using BSS. We attribute the three signals to ionized PAHs, neutral PAHs, and Very Small Grains (VSGs). The fit of the BSS extracted spectra with the PAH database further confirms the attribution to ionized and neutral PAHs and provides confidence in both methods for producing reliable results. The 11.0 micron feature is attributed to PAH cations while the 11.2 micron band is attributed to neutral PAHs. The VSG signal shows a characteristically asymmetric broad feature at 11.3 micron with an extended red wing. By combining the NASA Ames PAH IR Spectroscopic Database fit with the BSS method, the independent results of each method can be confirmed and some limitations of each method are overcome.
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PAH-related Very Small Grains in photodissociation regions: implications from molecular simulations
EAS Publications Series, 2011Co-Authors: Mathias Rapacioli, O Berne, C Joblin, Fernand Spiegelman, Baptiste Joalland, Aude Simon, André Mirtschink, J. Montillaud, D. TalbiAbstract:The analysis of mid-IR emission suggests that a population of PAH-related Very Small Grains containing a few hundreds of atoms are present in the deep regions of molecular clouds, although no specific species has been identified yet. In this review, we discuss several candidates for these Grains: neutral and ionised PAH clusters and complexes of PAHs with Si atoms. The theoretical modelling of the properties of such molecular complexes or nanoGrains is a challenging task. We first present an overview of quantum chemistry derived models which can be efficiently used on-the-fly in extensive sampling of the potential energy surfaces, as required by structural optimization, classical molecular dynamics or Monte Carlo algorithms. From the simulations, various observables can be determined, such as the binding energies, finite temperature IR spectra, nucleation and evaporation rates. We discuss the relevance of those candidates in the molecular clouds photodissociation regions and propose constrains and perspectives for the nature and size of those Very Small Grains.
J P Bernard - One of the best experts on this subject based on the ideXlab platform.
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variations between dust and gas in the diffuse interstellar medium iii changes in dust properties
The Astrophysical Journal, 2017Co-Authors: W T Reach, J P Bernard, T H Jarrett, Carl HeilesAbstract:We study infrared emission of 17 isolated, diffuse clouds with masses of order to test the hypothesis that grain property variations cause the apparently low gas-to-dust ratios that have been measured in those clouds. Maps of the clouds were constructed from Wide-field Infrared Survey Explorer (WISE) data and directly compared with the maps of dust optical depth from Planck. The mid-infrared emission per unit dust optical depth has a significant trend toward lower values at higher optical depths. The trend can be quantitatively explained by the extinction of starlight within the clouds. The relative amounts of polycyclic aromatic hydrocarbon and Very Small Grains traced by WISE, compared with large Grains tracked by Planck, are consistent with being constant. The temperature of the large Grains significantly decreases for clouds with larger dust optical depth; this trend is partially due to dust property variations, but is primarily due to extinction of starlight. We updated the prediction for molecular hydrogen column density, taking into account variations in dust properties, and find it can explain the observed dust optical depth per unit gas column density. Thus, the low gas-to-dust ratios in the clouds are most likely due to "dark gas" that is molecular hydrogen.
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dust processing in supernova remnants spitzer mips spectral energy distribution and infrared spectrograph observations
The Astrophysical Journal, 2011Co-Authors: W T Reach, Morten Andersen, Jeonghee Rho, J W Hewitt, J P BernardAbstract:We present Spitzer Multiband Imaging Photometer (MIPS) spectral energy distribution (SED) and Infrared Spectrograph (IRS) observations of 14 Galactic supernova remnants (SNRs) previously identified in the GLIMPSE survey. We find evidence for SNR/molecular cloud interaction through detection of [O I] emission, ionic lines, and emission from molecular hydrogen. Through blackbody fitting of the MIPS SEDs we find the large Grains to be warm, 29-66 K. The dust emission is modeled using the DUSTEM code and a three-component dust model composed of populations of big Grains (BGs), Very Small Grains (VSGs), and polycyclic aromatic hydrocarbons. We find the dust to be moderately heated, typically by 30-100 times the interstellar radiation field. The source of the radiation is likely hydrogen recombination, where the excitation of hydrogen occurred in the shock front. The ratio of VSGs to BGs is found for most of the molecular interacting SNRs to be higher than that found in the plane of the Milky Way, typically by a factor of 2-3. We suggest that dust shattering is responsible for the relative overabundance of Small Grains, in agreement with the prediction from dust destruction models. However, two of the SNRs are best fitted with a Very low abundance of carbon Grains to silicate Grains and with a Very high radiation field. A likely reason for the low abundance of Small carbon Grains is sputtering. We find evidence for silicate emission at 20 μm in their SEDs, indicating that they are young SNRs based on the strong radiation field necessary to reproduce the observed SEDs.
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Analysis of the emission of Very Small dust particles from Spitzer spectro-imagery data using blind signal separation methods
Astronomy and Astrophysics - A&A, 2007Co-Authors: O Berne, Mathias Rapacioli, J Thomas, C Joblin, J P Bernard, J D T Smith, Y. Deville, W. Reach, A AbergelAbstract:Context: This work was conducted as part of the SPECPDR program, dedicated to the study of Very Small particles and astrochemistry, in Photo-Dissociation Regions (PDRs). Aims: We present the analysis of the mid-IR spectro-imagery observations of Ced 201, NCG 7023 East and North-West and ? Ophiuchi West filament. Methods: Using the data from all four modules of the InfraRed Spectrograph onboard the Spitzer Space Telescope, we produced a spectral cube ranging from 5 to 35 ?m, for each one of the observed PDRs. The resulting cubes were analysed using Blind Signal Separation methods (NMF and FastICA). Results: For Ced 201, ? Ophiuchi West filament and NGC 7023 East, we find that two signals can be extracted from the original data cubes, which are 5 to 35 ?m spectra. The main features of the first spectrum are a strong continuum emission at long wavelengths, and a broad 7.8 ?m band. On the contrary, the second spectrum exhibits the classical Aromatic Infrared Bands (AIBs) and no continuum. The reconstructed spatial distribution maps show that the latter spectrum is mainly present at the cloud surface, close to the star whereas the first one is located slightly deeper inside the PDR. The study of the spectral energy distribution of Ced 201 up to 100 ?m suggests that, in cool PDRs, the 5-25 ?m continuum is carried by Very Small Grains (VSGs). The AIB spectra in the observed objects can be interpreted as the contribution of neutral and positively-charged Polycyclic Aromatic Hydrocarbons (PAHs). Conclusions: We extracted the 5 to 25 ?m emission spectrum of VSGs in cool PDRs, these Grains being most likely carbonaceous. We show that the variations of the mid-IR (5-35 ?m) spectra of PDRs can be explained by the photo-chemical processing of these VSGs and PAHs, VSGs being the progenitors of free PAHs. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Spectra are only available in electronic form (FITS files) at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/469/575
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analysis of the emission of Very Small dust particles from spitzer spectro imagery data using blind signal separation methods
arXiv: Astrophysics, 2007Co-Authors: O Berne, Mathias Rapacioli, J Thomas, Yannick Deville, C Joblin, W T Reach, J P Bernard, J D T Smith, A AbergelAbstract:This work was conducted as part of the SPECPDR program, dedicated to the study of Very Small particles and astrochemistry, in Photo-Dissociation Regions (PDRs). We present the analysis of the mid-IR spectro-imagery observations of Ced 201, NCG 7023 East and North-West and rho-Ophiuchi West filament. Using the data from all four modules of the InfraRed Spectrograph onboard the Spitzer Space Telescope, we produced a spectral cube ranging from 5 to 35 um for each one of the observed PDRs. The resulting cubes were analysed using Blind Signal Separation methods (NMF and FastICA). For Ced 201, rho-Ophiuchi West filament and NGC 7023 East, we find that two signals can be extracted from the original data cubes, which are 5 to 35 um spectra. The main features of the first spectrum are a strong continuum emission at long wavelengths, and a broad 7.8 um band. On the contrary, the second spectrum exhibits the classical Aromatic Infrared Bands (AIBs) and no continuum. The reconstructed spatial distribution maps show that the latter spectrum is mainly present at the cloud surface, close to the star whereas the first one is located slightly deeper inside the PDR. The study of the spectral energy distribution of Ced 201 up to 100 um suggests that, in cool PDRs, the 5-25 um continuum is carried by Very Small Grains (VSGs). The AIB spectra in the observed objects can be interpreted as the contribution of neutral and positively-charged Polycyclic Aromatic Hydrocarbons (PAHs). We extracted the 5 to 25 um emission spectrum of VSGs in cool PDRs, these Grains being most likely carbonaceous. We show that the variations of the mid-IR (5-35 um) spectra of PDRs can be explained by the photo-chemical processing of these VSGs and PAHs, VSGs being the progenitors of free PAH.
