Interstellar Gas Dynamics

1968 ◽  
Vol 1 (3) ◽  
pp. 96-96
Author(s):  
M.E. Dixon
Keyword(s):  
Chemical Composition ◽  
Interstellar Medium ◽  
Gas Dynamics ◽  
Young Stars ◽  
Observational Result ◽  
Interstellar Gas ◽  
Present Epoch ◽  
Metal Abundances

It is a well established observational result that young stars exhibit differences in chemical composition. The differences are comparatively large. For example, some stars have metal abundances as high as 3/2 solar-value while others have abundances as low as 1/2 solar-value. The result was obtained through spectroscopic and photoelectric studies of stars with ages of a few times 108 yr and indicates that the interstellar medium is chemically heterogeneous at the present epoch.

scholarly journals Final Discussion

1970 ◽  
Vol 39 ◽  
pp. 362-384
Author(s):  
R. N. Thomas
Keyword(s):  
Interstellar Medium ◽  
Energy Flow ◽  
Gas Dynamics ◽  
Present Form ◽  
Future Research ◽  
Interstellar Gas

In the present form the Final Discussion is divided into three sections: 1. Discussion on the Overall Energy Flow in the Interstellar Medium; 2. Summaries and Suggestions for Future Research (more or less prepared talks); 3. Summaries and Suggestions for Future Research (more or less free discussion). The discussion in Section 1 actually took place on Saturday, September 13, but it belongs in the Final Discussion. The (invited) summary papers, presented in Section 2, were given by Parker, van Woerden, and Kaplan. Section 3 starts with the remarks by Busemann on the interrelation between interstellar gas dynamics and aerodynamics, as viewed by an aerodynamicist; these remarks were made on Tuesday, September 16. The rest of Section 3 is taken up by the actual discussion held on the final day of the Symposium.

Supernovae and interstellar gas dynamics

1967 ◽  
Vol 31 ◽  
pp. 117-119
Author(s):  
F. D. Kahn ◽  
L. Woltjer
Keyword(s):  
Lower Limit ◽  
High Velocity ◽  
Gas Dynamics ◽  
Interstellar Cloud ◽  
Interstellar Gas ◽  
Random Motions ◽  
Relativistic Particles

The efficiency of the transfer of energy from supernovae into interstellar cloud motions is investigated. A lower limit of about 0·002 is obtained, but values near 0·01 are more likely. Taking all uncertainties in the theory and observations into account, the energy per supernova, in the form of relativistic particles or high-velocity matter, needed to maintain the random motions in the interstellar gas is estimated as 1051·4±1ergs.

scholarly journals Abundances in the Gaseous Galactic Halo

1998 ◽  
Vol 11 (1) ◽  
pp. 86-89
Author(s):  
Ulysses J. Sofia
Keyword(s):  
Interstellar Medium ◽  
Gas Phase ◽  
High Velocity ◽  
Galactic Halo ◽  
Solar Neighborhood ◽  
Local Interstellar Medium ◽  
The Galaxy ◽  
Metal Abundances ◽  
High Velocity Clouds

Abstract The well measured gas-phase abundances in the low halo suggest that this region of the Galaxy has total (gas plus dust) metal abundances which are close to those in the solar neighborhood. The gas-phase abundances in the halo are generally higher than those seen in the disk, however, this affect is likely due to the destruction of dust in the halo clouds. Observations of high velocity clouds (HVCs) in the halo suggest that these clouds have metal abundances which are substantially lower than those measured for the local interstellar medium. These determinations, however, are often of lower quality than those for the low halo because of uncertainties in the hydrogen abundances along the sightlines, in the incorporation of elements into dust, and in the partial ionization of the clouds.

scholarly journals The interstellar medium in young supernova remnants: key to the production of cosmic X-rays and $\gamma $-rays

2021 ◽  
Vol 366 (6) ◽  
Author(s):  
Hidetoshi Sano ◽  
Yasuo Fukui
Keyword(s):  
Interstellar Medium ◽  
Supernova Remnants ◽  
Cosmic Ray ◽  
High Energy ◽  
X Rays ◽  
Interstellar Gas ◽  
High Energy Radiation ◽  
Dense Cores ◽  
The Relationship ◽  
Turbulent Velocity Field

AbstractWe review recent progress in elucidating the relationship between high-energy radiation and the interstellar medium (ISM) in young supernova remnants (SNRs) with ages of ∼2000 yr, focusing in particular on RX J1713.7−3946 and RCW 86. Both SNRs emit strong nonthermal X-rays and TeV $\gamma $ γ -rays, and they contain clumpy distributions of interstellar gas that includes both atomic and molecular hydrogen. We find that shock–cloud interactions provide a viable explanation for the spatial correlation between the X-rays and ISM. In these interactions, the supernova shocks hit the typically pc-scale dense cores, generating a highly turbulent velocity field that amplifies the magnetic field up to 0.1–1 mG. This amplification leads to enhanced nonthermal synchrotron emission around the clumps, whereas the cosmic-ray electrons do not penetrate the clumps. Accordingly, the nonthermal X-rays exhibit a spatial distribution similar to that of the ISM on the pc scale, while they are anticorrelated at sub-pc scales. These results predict that hadronic $\gamma $ γ -rays can be emitted from the dense cores, resulting in a spatial correspondence between the $\gamma $ γ -rays and the ISM. The current pc-scale resolution of $\gamma $ γ -ray observations is too low to resolve this correspondence. Future $\gamma $ γ -ray observations with the Cherenkov Telescope Array will be able to resolve the sub-pc-scale $\gamma $ γ -ray distribution and provide clues to the origin of these cosmic $\gamma $ γ -rays.

scholarly journals Constraining the coherence scale of the interstellar magnetic field using TeV gamma-ray observations of supernova remnants

2020 ◽  
Vol 496 (2) ◽  
pp. 2448-2461 ◽  
Author(s):  
Matteo Pais ◽  
Christoph Pfrommer ◽  
Kristian Ehlert ◽  
Maria Werhahn ◽  
Georg Winner
Keyword(s):  
Magnetic Field ◽  
Interstellar Medium ◽  
Supernova Remnants ◽  
Gamma Ray ◽  
Galactic Cosmic Rays ◽  
Shock Acceleration ◽  
Interstellar Gas ◽  
Narrow Angle ◽  
Magnetohydrodynamic Simulations ◽  
Tev Gamma Rays

ABSTRACT Galactic cosmic rays (CRs) are believed to be accelerated at supernova remnant (SNR) shocks. In the hadronic scenario, the TeV gamma-ray emission from SNRs originates from decaying pions that are produced in collisions of the interstellar gas and CRs. Using CR-magnetohydrodynamic simulations, we show that magnetic obliquity-dependent shock acceleration is able to reproduce the observed TeV gamma-ray morphology of SNRs such as Vela Jr and SN1006 solely by varying the magnetic morphology. This implies that gamma-ray bright regions result from quasi-parallel shocks (i.e. when the shock propagates at a narrow angle to the upstream magnetic field), which are known to efficiently accelerate CR protons, and that gamma-ray dark regions point to quasi-perpendicular shock configurations. Comparison of the simulated gamma-ray morphology to observations allows us to constrain the magnetic coherence scale λB around Vela Jr and SN1006 to $\lambda _B \simeq 13_{-4.3}^{+13}$ pc and $\lambda _B \gt 200_{-40}^{+50}$ pc, respectively, where the ambient magnetic field of SN1006 is consistent with being largely homogeneous. We find consistent pure hadronic and mixed hadronic-leptonic models that both reproduce the multifrequency spectra from the radio to TeV gamma-rays and match the observed gamma-ray morphology. Finally, to capture the propagation of an SNR shock in a clumpy interstellar medium, we study the interaction of a shock with a dense cloud with numerical simulations and analytics. We construct an analytical gamma-ray model for a core collapse SNR propagating through a structured interstellar medium, and show that the gamma-ray luminosity is only biased by 30 per cent for realistic parameters.

scholarly journals Some Characteristics of Interstellar Gas in the Galaxy

1970 ◽  
Vol 39 ◽  
pp. 22-50 ◽  
Author(s):  
Harold F. Weaver
Keyword(s):  
Gas Dynamics ◽  
Theoretical Models ◽  
Structural Features ◽  
Interstellar Gas ◽  
Great Breadth ◽  
The Galaxy ◽  
The Subject

The task assigned for this review is to discuss structural features of the Galaxy as they may involve or relate to gas dynamics. Since a topic of such great breadth would permit discussion of essentially any aspect of the Galaxy, we shall narrow the view and direct attention primarily towards the larger-scale features of the system. In particular, effort will be made to place emphasis on those areas of the subject in which problems of interpretation exist and in which new theoretical models are needed.

scholarly journals Supershells

1988 ◽  
Vol 101 ◽  
pp. 447-459
Author(s):  
Richard McCray
Keyword(s):  
Star Formation ◽  
Radio Emission ◽  
Interstellar Medium ◽  
Milky Way ◽  
Disk Galaxy ◽  
Interstellar Gas ◽  
Irregular Galaxies ◽  
Nearby Galaxies ◽  
Gas Layer

AbstractRepeated supernovae from an OB association will, in a few ×107 yr, create a cavity of coronal gas in the interstellar medium, with radius > 100 pc, surrounded by a dense expanding shell of cool interstellar gas. Such a cavity will likely burst through the gas layer of a disk galaxy. Such holes and “supershells” have been observed in optical and H I radio emission maps of the Milky Way and other nearby galaxies. The gas swept up in the supershell is likely to become gravitationally unstable, providing a mechanism for propagating star formation that may be particularly effective in irregular galaxies.

Dependence of Silicon and Manganese Content in the Weld Metal on the Welding Current and Method of Gas Shielding

2015 ◽  
Vol 756 ◽  
pp. 92-96 ◽  
Author(s):  
Dmitry A. Chinakhov
Keyword(s):  
Chemical Composition ◽  
Weld Metal ◽  
Gas Dynamics ◽  
Gas Flow ◽  
Manganese Content ◽  
Welding Current ◽  
Mag Welding ◽  
Different Types ◽  
Considerable Impact ◽  
Electrode Metal

The influence of the welding current and method of gas shielding in MAG welding on the content of silicon and manganese is considered. Results of study of the welded specimens of steels 45 and 30HGSA when applying welding wire of different formulas and different types of gas shielding (traditional shielding and two-jet shielding) are given. It is established that in MAG welding the value of the welding current and the speed of the gas flow from the welding nozzle have a considerable impact on the chemical composition of the weld metal. The consumable electrode welding under double-jet gas shielding provides the directed gas-dynamics in the welding area and enables controlling the electrode metal transfer and the chemical composition of a weld.

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