Influence of Interstellar Dust on the Chemical Composition of Interstellar Gas-Dust Clouds

2014 ◽  
pp. 000-000
Author(s):  
Juris Kalvāns
Keyword(s):  
Chemical Composition ◽  
Interstellar Dust ◽  
Interstellar Gas ◽  
Dust Clouds

Extinction Curves, Distances, and Clumpiness of Diffuse Interstellar Dust Clouds

1999 ◽  
Vol 117 (5) ◽  
pp. 2226-2243 ◽  
Author(s):  
Arpad Szomoru ◽  
Puragra Guhathakurta
Keyword(s):  
Interstellar Dust ◽  
Dust Clouds

scholarly journals Formation of Molecular Hydrogen in Interstellar Space

1965 ◽  
Vol 7 ◽  
pp. 253-257
Author(s):  
H. F. P. Knaap ◽  
C. J. N. Van Den Meijdenberg ◽  
J. J. M. Beenakker ◽  
H. C. Van De Hulst
Keyword(s):  
Interstellar Dust ◽  
Interstellar Space ◽  
Interstellar Gas ◽  
Interstellar Clouds ◽  
Dark Clouds ◽  
Hydrogen Molecules ◽  
Large Factor ◽  
Dust Grain ◽  
Indirect Argument ◽  
Made In

Although Several Attempts at observing the interstellar hydrogen molecules in the ultraviolet or infrared are in preparation (ref. 1), these molecules are still undetected. They may form the most abundant unobserved constituent of the interstellar gas. The strongest indirect argument for the presence of these molecules lies in the fact that the density of atomic hydrogen observed by the 21-cm line goes down in some dark clouds, where the dust density and, presumably, the total gas density goes up by a large factor.Inasmuch as the density in the interstellar clouds is of the order of 10 atoms/cm3 and the temperature is only of the order of 100° K, any formation of molecules by atom-atom collisions is too slow to be of importance. The most eligible process for H2 formation is recombination on the surface of an interstellar dust grain. Rate estimates of this process have been made in various degrees of detail, as reported in references 2 to 4.

Normal OH Emission and Interstellar Dust Clouds

1968 ◽  
Vol 151 ◽  
pp. 919 ◽  
Author(s):  
Carl E. Heiles
Keyword(s):  
Interstellar Dust ◽  
Dust Clouds

scholarly journals Astrochemical relevance of VUV ionization of large PAH cations

2020 ◽  
Vol 641 ◽  
pp. A98 ◽  
Author(s):  
G. Wenzel ◽  
C. Joblin ◽  
A. Giuliani ◽  
S. Rodriguez Castillo ◽  
G. Mulas ◽  
...  
Keyword(s):  
Cross Sections ◽  
Density Functional ◽  
Interstellar Dust ◽  
Vacuum Ultraviolet ◽  
Branching Ratio ◽  
Molecular Size ◽  
Photoelectric Effect ◽  
Interstellar Gas ◽  
Ionization Cross Sections ◽  
The Impact

Context. As part of interstellar dust, polycyclic aromatic hydrocarbons (PAHs) are processed by an interaction with vacuum ultraviolet (VUV) photons emitted by hot stars. This interaction leads to the emission of not only the well-known aromatic infrared bands, but also electrons, which can significantly contribute to the heating of the interstellar gas. Aims. Our aim is to investigate the impact of molecular size on the photoionization properties of cationic PAHs. Methods. Trapped PAH cations of sizes between 30 and 48 carbon atoms were submitted to VUV photons in the range of 9–20 eV from the DESIRS beamline at the synchrotron SOLEIL. All resulting photoproducts including dications and fragment cations were mass-analyzed and recorded as a function of photon energy. Results. Photoionization is found to be predominant over dissociation at all energies, which differs from the conclusions of an earlier study on smaller PAHs. The photoionization branching ratio reaches 0.98 at 20 eV for the largest studied PAH. The photoionization threshold is observed to be between 9.1 and 10.2 eV, in agreement with the evolution of the ionization potential with size. Ionization cross sections were indirectly obtained and photoionization yields extracted from their ratio with theoretical photoabsorption cross sections, which were calculated using time-dependent density functional theory. An analytical function was derived to calculate this yield for a given molecular size. Conclusions. Large PAH cations could be efficiently ionized in H I regions and contribute to the heating of the gas by the photoelectric effect. Also, at the border of or in H II regions, PAHs could be exposed to photons of energy higher than 13.6 eV. Our work provides recipes to be used in astronomical models to quantify these points.

scholarly journals The role of wind driving in OB star bow nebulae

2020 ◽  
Vol 494 (2) ◽  
pp. 1838-1847
Author(s):  
Curtis Struck
Keyword(s):  
Interstellar Dust ◽  
Gas Flow ◽  
Ionization Front ◽  
Emission Region ◽  
Interstellar Gas ◽  
Weibel Instability ◽  
Peculiar Velocities ◽  
Interstellar Dust Grains ◽  
Energy And Momentum ◽  
Ir Emission

ABSTRACT Bow-shaped mid-infrared (mid-IR) emission regions have been discovered in satellite observations of numerous late-type O and early-type B stars with moderate velocities relative to the ambient interstellar medium. Previously, hydrodynamical bow shock models have been used to study this emission. It appears that such models are incomplete in that they neglect kinetic effects associated with long mean free paths of stellar wind particles, and the complexity of Weibel instability fronts. Wind ions are scattered in the Weibel instability and mix with the interstellar gas. However, they do not lose their momentum and most ultimately diffuse further into the ambient gas like cosmic rays, and share their energy and momentum. Lacking other coolants, the heated gas transfers energy into interstellar dust grains, which radiate it. This process, in addition to grain photoheating, provides the energy for the emission. A weak R-type ionization front, formed well outside the IR emission region, generally moderates the interstellar gas flow into the emission region. The theory suggests that the IR emission process is limited to cases of moderate stellar peculiar velocities, evidently in accord with the observations.

scholarly journals Interstellar Dust and the H2 Molecule

1965 ◽  
Vol 7 ◽  
pp. 259-264
Author(s):  
K. H. Schmidt
Keyword(s):  
Hydrogen Atom ◽  
Molecular Hydrogen ◽  
Interstellar Dust ◽  
Unit Volume ◽  
Formation Rate ◽  
Dust Particles ◽  
Interstellar Gas ◽  
The Past ◽  
Grain Surface ◽  
H2 Molecule

Nearly 20 Years Ago van de Hulst stated that the formation of molecular hydrogen occurs on the surfaces of the interstellar grains. (See ref. 1.) In the last years several authors discussed the problem of the interstellar abundance of the H2 molecule. (See refs. 2 to 9.) They all found that the percentage of the molecular hydrogen in the interstellar gas probably is much larger than had been thought in the past and that the essential mechanism of H2 formation is the formation on the particle surfaces. Therefore, the formation rate of interstellar H2 is a function of the area of the grain surface per unit volume, which is dependent on the average radius of the grains ā, on the number of dust particles per unit volume N(ā), and on the distribution function of the particle radii. The formation rate is determined by the density of the atomic hydrogen nH and the temperature of the interstellar gas Tgas. Finally, the formation rate of H2 depends on the probability π that an impinging hydrogen atom on a grain joins with another hydrogen atom to form a molecule.

scholarly journals Grain temperatures and infrared emission from interstellar dust clouds

1977 ◽  
Vol 180 (3) ◽  
pp. 323-337 ◽  
Author(s):  
S. Aiello ◽  
F. Mencaraglia ◽  
A. Blanco ◽  
A. Borghesi ◽  
E. Bussoletti
Keyword(s):  
Interstellar Dust ◽  
Infrared Emission ◽  
Dust Clouds

scholarly journals The Alignment of Interstellar Dust Clouds

1974 ◽  
Vol 168 (3) ◽  
pp. 639-650 ◽  
Author(s):  
P. B. Hopper ◽  
M. J. Disney
Keyword(s):  
Interstellar Dust ◽  
Dust Clouds

scholarly journals The apparent anticorrelation between the mass opacity of interstellar dust and the surface density of interstellar gas

2020 ◽  
Vol 494 (1) ◽  
pp. L48-L52 ◽  
Author(s):  
F D Priestley ◽  
A P Whitworth
Keyword(s):  
Spatial Variation ◽  
Surface Density ◽  
Interstellar Dust ◽  
Line Of Sight ◽  
Interstellar Gas ◽  
Dust Mass ◽  
Dust Evolution ◽  
Disc Galaxies

ABSTRACT Recent analyses of Herschel observations suggest that in nearby disc galaxies the dust mass opacity at $500 \, {\rm \mu m}$, κ500, decreases with increasing gas surface density, ΣISM. This apparent anticorrelation between κ500 and ΣISM is opposite to the behaviour expected from theoretical dust evolution models; in such models, dust in denser, cooler regions (i.e. regions of increased ΣISM) tends to grow and therefore to have increased κ500. We show, using a toy model, that the presence of a range of dust temperatures along the line of sight can lead to spuriously low estimated values of κ500. If in regions of higher ΣISM the range of dust temperatures extends to lower values (as seems likely), the magnitude of this effect may be sufficient to explain the apparent anticorrelation between κ500 and ΣISM. Therefore there may not be any need for spatial variation in the intrinsic dust properties that run counter to theoretical expectations.

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