The Origin and Development of Instabilities in Radiatively-driven Stellar Winds PDF Download
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Languages : en
Pages : 15
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Book Description
The numerous observational indicators of instability in the radiatively-driven winds of hot stars are review briefly, followed by a summary of the present theoretical understanding of the linear instability of such winds. This provides the motivation for the hydrodynamic simulation, the major thrust of the paper. A serious approximation that must be made in order to reduce the cost of the simulations to a reasonable level--the absorption approximation for the radiation force--is discussed in some detail. The hydrodynamic methods are described briefly, and then the computational results for winds models computed in the absorption approximation are discussed. The most notable results pertain to the critical nature of the ratio v{sub th}/a of the intrinsic line width to the sound speed. When this ratio is large, only a negligible wind results; when the ratio is small, the wind executes permanent self-excited oscillations; in an intermediate range the wind is globally stable, but acts as a powerful wave amplifier. The morphology of the oscillations--strong rarefactions and reverse shocks--is described and related to Abbott's linear theory, and the possible connection to observations is mentioned. 30 refs.
Author:
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ISBN:
Category :
Languages : en
Pages : 15
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Book Description
The numerous observational indicators of instability in the radiatively-driven winds of hot stars are review briefly, followed by a summary of the present theoretical understanding of the linear instability of such winds. This provides the motivation for the hydrodynamic simulation, the major thrust of the paper. A serious approximation that must be made in order to reduce the cost of the simulations to a reasonable level--the absorption approximation for the radiation force--is discussed in some detail. The hydrodynamic methods are described briefly, and then the computational results for winds models computed in the absorption approximation are discussed. The most notable results pertain to the critical nature of the ratio v{sub th}/a of the intrinsic line width to the sound speed. When this ratio is large, only a negligible wind results; when the ratio is small, the wind executes permanent self-excited oscillations; in an intermediate range the wind is globally stable, but acts as a powerful wave amplifier. The morphology of the oscillations--strong rarefactions and reverse shocks--is described and related to Abbott's linear theory, and the possible connection to observations is mentioned. 30 refs.
Author: L. Crivellari
Publisher: Springer Science & Business Media
ISBN: 9401135541
Category : Science
Languages : en
Pages : 459
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Book Description
The theory of stellar atmospheres is one of the most important branches of modern astrophysics. It is first of all a major tool for understanding all aspects of stars. As the physical properties of their outer layers can now be found with high precision, firm conclusions can be drawn about the internal structure and evolution of stars. Moreover, improvements in our knowledge of the chemical composition of stars is shedding new light on the chemical evolution of galaxies and of the Universe as a whole. Because the outer layers of stars are among the best-understood astrophysical objects, the theory of stellar atmospheres plays an important role in the study of many other types of objects. These include planetary nebulae, H II regions, interstellar matter, and objects of interest in high-energy astrophysics, such as accretion disks (close binaries, dwarf novae, cataclysmic variables, quasars, active galactic nuclei), pulsar magnetospheres, and Seyfert galaxies. Finally, as stars provide a laboratory in which plasmas can be studied under more extreme conditions than on earth, the study of stellar atmospheres has strong connections with modern physics. Astronomical observations provided a vital stimulus in the early stages of quantum theory and atomic physics; even today topics such as low-temperature dielectronic recombination develop hand in hand with the interpretation of stellar and nebular spectra. Early work on MHD was similiarly motivated. Many such connections remain to be explored.
Author: Raymond G. Carlberg
Publisher: 1978.
ISBN:
Category : Stars
Languages : en
Pages : 366
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Category : Power resources
Languages : en
Pages : 936
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Author: Astronomisches Rechen-Institut
Publisher: Springer Science & Business Media
ISBN: 3662123762
Category : Science
Languages : en
Pages : 1592
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"Astronomy and Astrophysics Abstracts" appearing twice a year has become oneof the fundamental publications in the fields of astronomy, astrophysics andneighbouring sciences. It is the most important English-language abstracting journal in the mentioned branches. The abstrats are classified under more than a hundred subject categories, thus permitting a quick survey of the whole extended material. The AAA is a valuable and important publication for all students and scientists working in the fields of astronomy and related sciences. As such it represents a necessary ingredient of any astronomical library all over the world.
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Category : Aeronautics
Languages : en
Pages : 704
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Category : Power resources
Languages : en
Pages : 900
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Semiannual, with semiannual and annual indexes. References to all scientific and technical literature coming from DOE, its laboratories, energy centers, and contractors. Includes all works deriving from DOE, other related government-sponsored information, and foreign nonnuclear information. Arranged under 39 categories, e.g., Biomedical sciences, basic studies; Biomedical sciences, applied studies; Health and safety; and Fusion energy. Entry gives bibliographical information and abstract. Corporate, author, subject, report number indexes.
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Category : Power resources
Languages : en
Pages : 676
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Category :
Languages : en
Pages : 1120
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Author: C. Chiosi
Publisher: Springer Science & Business Media
ISBN: 9400985002
Category : Science
Languages : en
Pages : 562
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The IAU Colloquium No. 59, "The effects of mass loss on Stellar Evolution" was held on September 15-19, 1980 at the International Centre for Theoretical Physics, Miramare, Trieste (Italy), under the auspices of the IAU Executive Co~ mittee and the Italian National Council of Research. The planning of this conference began two years ago du ring the IAU Symposium No. 83 "Mass loss and evolution of 0 type stars" (Qualicum Beach, Victoria, Canada) when we felt that mass loss and its effects on the evolution of stars was too broad a subject for being confined to 0 type stars only. Therefore we thought that a conference dealing with the general problem of mass loss across the whole HR diagram would have been of interest to all people working in the field. The main idea was that bringing together Astronomers and Astrophysicists of the widest range of interests and e~ pertize - all in some way related to the problem of mass loss from stars - would have spurred thorough discussions on the many aspects and implications of this topic. We hope this goal has been achieved. Furthermore, the most recent observational and theoreti cal developments on the problem of mass loss from early ty pe stars avoided this meeting to be a simple updating of the Qualicum Beach Symposium as far as this issue is concerned.
