scholarly journals C2 and Diffuse Interstellar Bands

2013 ◽  
Vol 9 (S297) ◽  
pp. 121-124 ◽  
Author(s):  
M. Kaźmierczak ◽  
M. Schmidt ◽  
T. Weselak ◽  
G. Galazutdinov ◽  
J. Krełowski
Keyword(s):  
Interstellar Clouds ◽  
Physical Conditions ◽  
Diffuse Interstellar Bands ◽  
Carbon Molecules ◽  
Long Chain

AbstractC2, the simplest multicarbon molecule is a useful astronomical tool, because the analysis of its lines allows to determine the physical conditions in interstellar clouds. C2 abundances give information about the chemistry of interstellar clouds, especially on the pathway to the formation of long-chain carbon molecules, which may be connected with carriers of diffuse interstellar bands (Douglas 1977, Thorburn et al. 2003). Here we summarize all relations between C2 and diffuse interstellar bands (DIBs).

scholarly journals Diffuse Cloud Models: Successes and Challenges

2013 ◽  
Vol 9 (S297) ◽  
pp. 311-320
Author(s):  
E. Roueff ◽  
M. Ruaud ◽  
F. Le Petit ◽  
B. Godard ◽  
J. Le Bourlot
Keyword(s):  
Radiation Field ◽  
Ionization Rate ◽  
Interstellar Clouds ◽  
Physical Conditions ◽  
Cloud Models ◽  
Diffuse Interstellar Bands ◽  
Molecular Transition ◽  
Diffuse Cloud ◽  
General Physical ◽  
Successes And Challenges

AbstractWe present the general physical conditions thought to be present in diffuse interstellar clouds. The radiation field is driving the atomic to molecular transition and the resulting physical conditions. We focus on the recent observational signatures of significant values of the cosmic ionization rate (10−16 - 10−15 s−1) which should also impact the clues to Diffuse interstellar Bands.

Diffuse Interstellar Bands: Physical Conditions That Facilitate the Formation or Preservation of Their Carriers

1998 ◽  
Vol 493 (1) ◽  
pp. 217-221 ◽  
Author(s):  
J. Krełowski ◽  
G. A. Galazutdinov ◽  
F. A. Musaev
Keyword(s):  
Physical Conditions ◽  
Diffuse Interstellar Bands

scholarly journals SOC program for dust continuum radiative transfer

2019 ◽  
Vol 622 ◽  
pp. A79 ◽  
Author(s):  
Mika Juvela
Keyword(s):  
Monte Carlo ◽  
Radiative Transfer ◽  
Convergence Rates ◽  
Dust Emission ◽  
Interstellar Clouds ◽  
Physical Conditions ◽  
Cloud Models ◽  
Order Of Magnitude ◽  
Speed Up ◽  
Run Time

Context. Thermal dust emission carries information on physical conditions and dust properties in many astronomical sources. Because observations represent a sum of emission along the line of sight, their interpretation often requires radiative transfer (RT) modelling. Aims. We describe a new RT program, SOC, for computations of dust emission, and examine its performance in simulations of interstellar clouds with external and internal heating. Methods. SOC implements the Monte Carlo RT method as a parallel program for shared-memory computers. It can be used to study dust extinction, scattering, and emission. We tested SOC with realistic cloud models and examined the convergence and noise of the dust-temperature estimates and of the resulting surface-brightness maps. Results. SOC has been demonstrated to produce accurate estimates for dust scattering and for thermal dust emission. It performs well with both CPUs and GPUs, the latter providing a speed-up of processing time by up to an order of magnitude. In the test cases, accelerated lambda iterations (ALIs) improved the convergence rates but was also sensitive to Monte Carlo noise. Run-time refinement of the hierarchical-grid models did not help in reducing the run times required for a given accuracy of solution. The use of a reference field, without ALI, works more robustly, and also allows the run time to be optimised if the number of photon packages is increased only as the iterations progress. Conclusions. The use of GPUs in RT computations should be investigated further.

Long chain carbon molecules and diffuse interstellar lines

Nature ◽  
1979 ◽  
Vol 278 (5706) ◽  
pp. 722-723 ◽  
Author(s):  
G. F. MITCHELL ◽  
W. T. HUNTRESS
Keyword(s):  
Carbon Molecules ◽  
Long Chain

scholarly journals Diffuse Interstellar Bands – The Unidentified Part of the Interstellar Absorption Spectrum

1989 ◽  
Vol 135 ◽  
pp. 67-86 ◽  
Author(s):  
Jacek Krełowski
Keyword(s):  
Absorption Spectrum ◽  
Line Of Sight ◽  
Optical Parameters ◽  
Interstellar Matter ◽  
Molecular Absorption ◽  
Interstellar Clouds ◽  
Diffuse Interstellar Bands ◽  
Intensity Ratios ◽  
Molecular Abundances

The unidentified (since 1921) diffuse interstellar bands (DIBs) are discussed together with their relations to other interstellar absorptions sucn as: continuous extinction, polarization and atomic or molecular absorption lines. It is shown that DIBs do not form the absorption spectrum of one agent, but probably of several (3 or more). DIBs as well as other interstellar absorptions are usually formed in several clouds along a line-of-sight. Thus, they suffer Doppler splitting; the first high resolution profiles free of the latter effect are described. Since single interstellar clouds may differ not only in radial velocities but also in many physical (optical) parameters, the observed interstellar absorptions are ill-defined averages over all clouds situated along any line-of-sight. It is of basic importance to determine not only the single cloud profiles of diffuse bands, but also their relations to other interstellar absorptions in the same clouds. Intensity ratios of DIBs are shown to be sensitive to the shapes of extinction curves, depletion patterns of elements and molecular abundances in the considered clouds. The sensitivity of the DIBs to the variation in polarization is less documented but probably also present. Thus the diffuse lines are presented as the unidentified part of the absorption spectrum of interstellar matter. Their identification depends on the determination of their relations to other interstellar absorptions which must be determined precisely.

scholarly journals Probing the missing link between the diffuse interstellar bands and the total-to-selective extinction ratio $R_V\,\!-\!$ I. Extinction versus reddening

2019 ◽  
Vol 489 (1) ◽  
pp. 708-713 ◽  
Author(s):  
Kaijun Li ◽  
Aigen Li ◽  
F Y Xiang
Keyword(s):  
Extinction Ratio ◽  
Interstellar Extinction ◽  
Extinction Curve ◽  
Interstellar Clouds ◽  
Diffuse Interstellar Bands ◽  
Hydrogen Column Density ◽  
Wide Range ◽  
Chemical Conditions ◽  
Physical And Chemical ◽  
Selective Extinction

ABSTRACT The carriers of the still (mostly) unidentified diffuse interstellar bands (DIBs) have been a long-standing mystery ever since their first discovery exactly 100 yr ago. In recent years, the ubiquitous detection of a large number of DIBs in a wide range of Galactic and extragalactic environments has led to renewed interest in connecting the occurrence and properties of DIBs to the physical and chemical conditions of the interstellar clouds, with particular attention paid to whether the DIB strength is related to the shape of the interstellar extinction curve. To shed light on the nature and origin of the DIB carriers, we investigate the relation between the DIB strength and RV, the total-to-selective extinction ratio, which characterizes how the extinction varies with wavelength (i.e. the shape of the extinction curve). We find that the DIB strength and RV are not related if we represent the strength of a DIB by its reddening-normalized equivalent width (EW), in contrast to the earlier finding of an anticorrelation in which the DIB strength is measured by the extinction-normalized EW. This raises a fundamental question about the appropriate normalization for the DIB EW. We argue that the hydrogen column density is a more appropriate normalization than extinction and reddening.

scholarly journals Broadband Cavity Enhanced Absorption Spectroscopy: A New Approach to Search for DIB Carriers

2013 ◽  
Vol 9 (S297) ◽  
pp. 281-285
Author(s):  
A. J. Walsh ◽  
D. Zhao ◽  
W. Ubachs ◽  
H. Linnartz
Keyword(s):  
Absorption Spectroscopy ◽  
Broad Band ◽  
Incoherent Light ◽  
New Approach ◽  
Interstellar Clouds ◽  
Enhanced Absorption ◽  
Cavity Enhanced Absorption Spectroscopy ◽  
Diffuse Interstellar Bands ◽  
Planar Plasma ◽  
Set Up

AbstractA new and sensitive set-up to swiftly test proposed carriers of the diffuse interstellar bands (DIBs), over a relatively broad spectral range, is described. The instrument utilizes broad-band cavity enhanced absorption spectroscopy (BBCEAS) and incorporates an optomechanical shutter to modulate light from a continuous incoherent light source. A pulsed supersonically expanding planar plasma expansion is used to mimic conditions in translucent interstellar clouds. Measurements of plasma durations as low as 400 μs are possible. The sensitivity is estimated to be better than 10 ppm/pass, measured with an effective exposure time of only ca. 1 s. The performance and potential of the instrument is demonstrated on spectra of C5H, C6H and C9H3 recorded through expanding hydrocarbon plasma.

scholarly journals Mass Outflow in Molecular Clouds: A New Phase in the Evolution of Newly-Formed Stars?

1983 ◽  
Vol 6 ◽  
pp. 686-706 ◽  
Author(s):  
R. Genzel ◽  
D. Downes
Keyword(s):  
Molecular Clouds ◽  
Sequence Evolution ◽  
Interstellar Clouds ◽  
Physical Conditions ◽  
Long Duration ◽  
Mass Outflow ◽  
Infrared Sources ◽  
T Tau ◽  
The Impact ◽  
New Phase

Molecular gas with velocity dispersions exceeding 100 km s-1 toward dense, interstellar clouds was discovered by microwave observers about a decade ago. It has now been established that this high velocity gas is a result of violent mass outflows (winds) originating from T-Tau stars, compact infrared sources or ultra-compact HII regions at the cores of the clouds. The mass outflow phenomena occur in regions of star formation covering five orders of magnitude in luminosity, and are of long duration . The observations suggest that violent mass loss is a new, important phase in the pre-main sequence evolution of newly-formed stars more massive than a few solar masses. The impact of the flows on the energy balance and dynamical stability of molecular clouds may be substantial. This review is mainly a summary of the observational facts, and gives a description of the physical conditions in an outflow zone. The impact of the flows on molecular clouds is discussed. Recent reviews of the outflow phenomena can also be found in (1, 2, 3, ).

scholarly journals Chemistry in Shocks

1989 ◽  
Vol 8 ◽  
pp. 375-382
Author(s):  
T.W. Hartquist
Keyword(s):  
Molecular Clouds ◽  
Molecular Data ◽  
Interstellar Chemistry ◽  
Interstellar Clouds ◽  
Chemical Structures ◽  
Physical Conditions ◽  
Classic Problem ◽  
Diffuse Cloud ◽  
Diffuse Clouds ◽  
Chemical Influence

ABSTRACTThe column densities of interstellar CH+, first detected about fifty years ago, cannot be explained with models of the chemistry in low temperature gas. The resolution of this classic problem is necessary for us to have confidence in our understanding of interstellar chemistry and its role in determining the physical conditions in interstellar clouds and in the utility of molecular abundance measurements as diagnostics. The possibility that the observed CH+ is formed primarily in shocks in diffuse clouds is addressed. The way in which the chemistry affects the structure of such a diffuse cloud shock is also discussed. The analogous chemical influence on the structures of shocks in dense molecular clouds is also considered as is the possibility that gas in some dense molecular clouds passes repeatedly through dynamical cycles and is shocked frequently enough to influence the global chemical structures in those clouds. Some atomic and molecular data needs are mentioned.

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