The Experts below are selected from a list of 45 Experts worldwide ranked by ideXlab platform
B T Draine - One of the best experts on this subject based on the ideXlab platform.
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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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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).
D S Wiebe - One of the best experts on this subject based on the ideXlab platform.
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the evolution of hydrocarbon dust grains in the interstellar medium and its influence on the infrared spectra of dust
arXiv: Solar and Stellar Astrophysics, 2016Co-Authors: M S Murga, S A Khoperskov, D S WiebeAbstract:We present evolutionary calculations for the size and aromatization degree distributions of interstellar dust grains, driven by theIR destruction by radiation, collisions with gas particles, and shattering due to grain-grain collisions. Based on these calculations we model dust Emission spectra. The initial grain size distribution play the important role in the evolution of an ensemble of dust particles. Radiation in the considered intensity range mostly aromatizes grains. The smallest grains are mainly destructed via sputtering by collisions with gas particles. There are no grains smaller than 20~\AA\ in the medium at relative gas-dust velocities more than 50~km/s, which is typical for shocks in supernova remnants. The IR Emission Spectrum changes significantly due to the dust evolution depending on the adopted grain properties, in particular, on the energy of the C--C bonds ($E_0$). Aromatic bands in the near-IR (2--15~$\mu$m) are absent, if $E_0$ is low, even when the medium properties correspond to the average interstellar medium in our Galaxy. As in reality these bands are observed, high $E_0$ values are more preferable. We consider dependence of the Emission intensity ratios for various photometric bands on the medium properties. The aromatization degree of small grains shows up most strongly in the $I_{3.4}/I_{11.3}$ intensity ratio while the fraction of aromatic grains in the total dust mass influences the $I_{3.3}/I_{70+160}$ ratio.
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the evolution of hydrocarbon dust grains in the interstellar medium and its influence on the infrared spectra of dust
Astronomy Reports, 2016Co-Authors: M S Murga, S A Khoperskov, D S WiebeAbstract:Computations of the evolution of the distributions of the size and degree of aromatization of interstellar dust grains, destruction by radiation and collisions with gas particles, and fragmentation during collisions with other grains are presented. The results of these computations are used to model dust Emission spectra. The evolution of an ensemble of dust particles sensitively depends on the initial size distribution of the grains. Radiation in the considered range of fluxes mainly aromatizes grains. With the exception of the smallest grains, it is mainly erosion during collisions with gas particles that leads to the destruction of grains. In the presence of particle velocities above 50 km/s, characteristic for shocks in supernova remnants, grains greater than 20 A in size are absent. The IR Emission Spectrum changes appreciably during the evolution of the dust, and depends on the adopted characteristics of the grains, in particular, the energy of theIR C–Cbonds (E 0). Aromatic bands are not observed in the near-IR (2–15 μm) when E 0 is low, even when the medium characteristics are typical for the average interstellarmedium in our Galaxy; this indicates a preference for high E 0 values. The influence of the characteristics of the medium on the intensity ratios for the dust Emission in various photometric bands is considered. The I 3.4/I 11.3 intensity ratio is most sensitive to the degree of aromatization of small grains. The I 3.3/I 70+160 ratio is a sensitive indicator of the contribution of aromatic grains to the total mass of dust.
S A Khoperskov - One of the best experts on this subject based on the ideXlab platform.
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the evolution of hydrocarbon dust grains in the interstellar medium and its influence on the infrared spectra of dust
arXiv: Solar and Stellar Astrophysics, 2016Co-Authors: M S Murga, S A Khoperskov, D S WiebeAbstract:We present evolutionary calculations for the size and aromatization degree distributions of interstellar dust grains, driven by theIR destruction by radiation, collisions with gas particles, and shattering due to grain-grain collisions. Based on these calculations we model dust Emission spectra. The initial grain size distribution play the important role in the evolution of an ensemble of dust particles. Radiation in the considered intensity range mostly aromatizes grains. The smallest grains are mainly destructed via sputtering by collisions with gas particles. There are no grains smaller than 20~\AA\ in the medium at relative gas-dust velocities more than 50~km/s, which is typical for shocks in supernova remnants. The IR Emission Spectrum changes significantly due to the dust evolution depending on the adopted grain properties, in particular, on the energy of the C--C bonds ($E_0$). Aromatic bands in the near-IR (2--15~$\mu$m) are absent, if $E_0$ is low, even when the medium properties correspond to the average interstellar medium in our Galaxy. As in reality these bands are observed, high $E_0$ values are more preferable. We consider dependence of the Emission intensity ratios for various photometric bands on the medium properties. The aromatization degree of small grains shows up most strongly in the $I_{3.4}/I_{11.3}$ intensity ratio while the fraction of aromatic grains in the total dust mass influences the $I_{3.3}/I_{70+160}$ ratio.
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the evolution of hydrocarbon dust grains in the interstellar medium and its influence on the infrared spectra of dust
Astronomy Reports, 2016Co-Authors: M S Murga, S A Khoperskov, D S WiebeAbstract:Computations of the evolution of the distributions of the size and degree of aromatization of interstellar dust grains, destruction by radiation and collisions with gas particles, and fragmentation during collisions with other grains are presented. The results of these computations are used to model dust Emission spectra. The evolution of an ensemble of dust particles sensitively depends on the initial size distribution of the grains. Radiation in the considered range of fluxes mainly aromatizes grains. With the exception of the smallest grains, it is mainly erosion during collisions with gas particles that leads to the destruction of grains. In the presence of particle velocities above 50 km/s, characteristic for shocks in supernova remnants, grains greater than 20 A in size are absent. The IR Emission Spectrum changes appreciably during the evolution of the dust, and depends on the adopted characteristics of the grains, in particular, the energy of theIR C–Cbonds (E 0). Aromatic bands are not observed in the near-IR (2–15 μm) when E 0 is low, even when the medium characteristics are typical for the average interstellarmedium in our Galaxy; this indicates a preference for high E 0 values. The influence of the characteristics of the medium on the intensity ratios for the dust Emission in various photometric bands is considered. The I 3.4/I 11.3 intensity ratio is most sensitive to the degree of aromatization of small grains. The I 3.3/I 70+160 ratio is a sensitive indicator of the contribution of aromatic grains to the total mass of dust.
G Carugno - One of the best experts on this subject based on the ideXlab platform.
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density induced modifications of the IR Emission Spectrum of xe 2 excimers in dense gas
IEEE Transactions on Dielectrics and Electrical Insulation, 2009Co-Authors: A F Borghesani, G CarugnoAbstract:The infrared Emission Spectrum of Xe2 excimers produced by IRradiating Xe gas with high-energy electrons has been monitored as a function of density up to 3.3 MPa at room temperature. Excimer decay yields a broad continuum centered around 7800 cm-1 of width 900 cm-1 at 0.1 MPa. The Spectrum shape is consistent with a bound-free molecular transition between 0u + and 0g + states correlated with 6p and 6s atomic limits. Upon increasing density, the Spectrum is strongly red-shifted and broadened. The present measurements confIRm preliminary results obtained in a smaller density range. The shift is explained by the dielectric screening exerted by the gas atoms on the optically active electron-ionic molecular core interaction, and by quantum multiple scattering effects of the electron scattered off the gas atoms. The latter effect links this experiment to electron transport experiments in non-polar gases. The different Spectrum broadening in pure Xe and in an Ar-Xe mixture is believed to be due to quantum indistinguishability of identical particles.
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dielectric screening multiple scattering and quantum indistinguishability effects in the IR Emission Spectrum of xe _2 excimers in dense xe gas
arXiv: Atomic Physics, 2008Co-Authors: A F Borghesani, G CarugnoAbstract:We report new measurements of the infrared Emission Spectrum of Xe$_{2}$ excimers produced by electron impact in dense gas at room temperature. These measurements extend the density range previously explored by a factor of two. We have now reached a pressure $P\approx 3.3 $MPa, corresponding to a gas density $N\approx 8\cdot 10^{26} $m$^{-3}$ in both pure Xe gas and in a Ar--Xe mixture. The analysis of the changes of the Spectrum induced by the interaction with the gaseous envIRonment shows how cooperative-- and many-body effects develop with increasing density. We %will also show that quantum effects related to the indistinguishability of identical particles are observed even at such high temperature.
Yannick Deville - One of the best experts on this subject based on the ideXlab platform.
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Extended Red Emission and the evolution of carbonaceous nanograins in NGC 7023
Astronomy and Astrophysics - A&A, 2008Co-Authors: O Berne, C Joblin, Mathias Rapacioli, J Thomas, J C Cuillandre, Yannick DevilleAbstract:Context: Extended Red Emission (ERE) was recently attributed to the photo-luminescence of either doubly ionized Polycyclic Aromatic Hydrocarbons (PAH++), or charged PAH dimers ([PAH{2}] ^+). Aims: We analysed the visible and mid-infrared (mid-IR) dust Emission in the North-West and South photo-dissociation regions of the reflection nebula NGC 7023. Methods: Using a blind signal separation method, we extracted the map of ERE from images obtained with the Hubble Space Telescope, and at the Canada France Hawaii Telescope. We compared the extracted ERE image to the distribution maps of the mid-IR Emission of Very Small Grains (VSGs), neutral and ionized PAHs (PAH0 and PAH^+) obtained with the Spitzer Space Telescope and the Infrared Space Observatory. Results: ERE is dominant in transition regions where VSGs are being photo-evaporated to form free PAH molecules, and is not observed in regions dominated by PAH^+. Its carrier makes a minor contribution to the mid-IR Emission Spectrum. Conclusions: These results suggest that the ERE carrier is a transition species formed during the destruction of VSGs. [PAH{2}] + appear as good candidates but PAH++ molecules seem to be excluded. 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. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program 9471. Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands and the United Kingdom) and with the participation of ISAS and NASA.
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extended red Emission and the evolution of carbonaceaous nanograins in ngc 7023
arXiv: Astrophysics, 2008Co-Authors: O Berne, C Joblin, Mathias Rapacioli, J Thomas, J C Cuillandre, Yannick DevilleAbstract:Extended Red Emission (ERE) was recently attributed to the photo-luminescence of either doubly ionized Polycyclic Aromatic Hydrocarbons (PAH$^{++}$), or charged PAH dimers. We analysed the visible and mid-infrared (mid-IR) dust Emission in the North-West and South photo-dissociation regions of the reflection nebula NGC 7023.Using a blind signal separation method, we extracted the map of ERE from images obtained with the Hubble Space Telescope, and at the Canada France Hawaii Telescope. We compared the extracted ERE image to the distribution maps of the mid-IR Emission of Very Small Grains (VSGs), neutral and ionized PAHs (PAH$^0$ and PAH$^+$) obtained with the Spitzer Space Telescope and the Infrared Space Observatory. ERE is dominant in transition regions where VSGs are being photo-evaporated to form free PAH molecules, and is not observed in regions dominated by PAH$^+$. Its carrier makes a minor contribution to the mid-IR Emission Spectrum. These results suggest that the ERE carrier is a transition species formed during the destruction of VSGs. Singly ionized PAH dimers appear as good candidates but PAH$^{++}$ molecules seem to be excluded.
