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Author: Lynn Buchele
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 64
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Book Description
Accurate stellar modeling requires using our understanding of phenomena far smaller than humans can observe to study some of the largest objects in the universe. One quantity that bridges this gap is the mean opacity, which uses knowledge about atomic and molecular interactions with light to inform how photons carry energy through a star. As the mean opacity depends on both the quantum mechanics of atoms and molecules and the macroscopic properties of the star (temperature, density, composition) it can be tricky to calculate. Traditionally, stellar modeling programs avoid the time-consuming computation of opacity by interpolating off of pre-made opacity tables. However, this interpolation introduces the possibility of error. In low-temperature areas of a star (less than 10,000K), this error is likely to be largest when the composition of the star differs from the composition used to create the tables. One way to examine this error is to model stars using low-temperature opacity values calculated on-the-fly. In this case, on-the-fly means using opacity calculated as the star is being modeled by a low-temperature opacity code using the exact temperature, density, and composition of each region within the star. This work describes the process of adapting the Atlas Opacity Program (ATOP) for use as an on-the-fly opacity code and discusses the results of using on-the-fly opacity values for several stellar evolution models created with the Modules for Experiments in Stellar Astrophysics (MESA) code. These models show that the effect of using on-the-fly opacity is more pronounced in models where the relative abundance of carbon to oxygen in the outer layers of the star changes significantly over the course of the star’s evolution.
Author: Lynn Buchele
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 64
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Book Description
Accurate stellar modeling requires using our understanding of phenomena far smaller than humans can observe to study some of the largest objects in the universe. One quantity that bridges this gap is the mean opacity, which uses knowledge about atomic and molecular interactions with light to inform how photons carry energy through a star. As the mean opacity depends on both the quantum mechanics of atoms and molecules and the macroscopic properties of the star (temperature, density, composition) it can be tricky to calculate. Traditionally, stellar modeling programs avoid the time-consuming computation of opacity by interpolating off of pre-made opacity tables. However, this interpolation introduces the possibility of error. In low-temperature areas of a star (less than 10,000K), this error is likely to be largest when the composition of the star differs from the composition used to create the tables. One way to examine this error is to model stars using low-temperature opacity values calculated on-the-fly. In this case, on-the-fly means using opacity calculated as the star is being modeled by a low-temperature opacity code using the exact temperature, density, and composition of each region within the star. This work describes the process of adapting the Atlas Opacity Program (ATOP) for use as an on-the-fly opacity code and discusses the results of using on-the-fly opacity values for several stellar evolution models created with the Modules for Experiments in Stellar Astrophysics (MESA) code. These models show that the effect of using on-the-fly opacity is more pronounced in models where the relative abundance of carbon to oxygen in the outer layers of the star changes significantly over the course of the star’s evolution.
Author: Aditya Sharma
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 59
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Book Description
Stellar evolution is studied through computational models of stars since any perceived change in the stars can take thousands if not millions of years. One of the physical quantities that defines the evolution of a star is known as the opacity. Opacity of a material determines how much electromagnetic radiation passes through the material. Scattering and absorption processes in the radiative region of the star determine the opacity of that region and regulate radiative energy flow in the star. The mean opacity which is averaged over all wavelengths depends on the temperature, density, and the composition of the material in the star. Currently, tables of mean opacities are used in stellar modeling. These opacities are given as functions of temperature and density and the tables are made for several compositions which changes with evolution of the star. At low temperatures, formation of molecules and dust grains can affect the mean opacity. In this study, low-temperature opacity tables are made with opacity codes ATOP and PHOENIX and stellar models produced with these opacity tables with the stellar evolution code MESA are compared. In addition, the effect of initial elemental abundance sets and molecular data sources on stellar evolution is studied. Finally, the impact of low-temperature opacities on the pace of stellar evolution is analyzed with stellar isochrones. The results show that there is negligible difference between stellar models produced with ATOP and PHOENIX and with different molecular data sources. However, changing the initial elemental abundance set generated significant changes in stellar evolution.
Author: Ivan Hubeny
Publisher: Princeton University Press
ISBN: 1400852730
Category : Science
Languages : en
Pages : 944
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Book Description
The most authoritative synthesis of the quantitative spectroscopic analysis of stellar atmospheres This book provides an in-depth and self-contained treatment of the latest advances achieved in quantitative spectroscopic analyses of the observable outer layers of stars and similar objects. Written by two leading researchers in the field, it presents a comprehensive account of both the physical foundations and numerical methods of such analyses. The book is ideal for astronomers who want to acquire deeper insight into the physical foundations of the theory of stellar atmospheres, or who want to learn about modern computational techniques for treating radiative transfer in non-equilibrium situations. It can also serve as a rigorous yet accessible introduction to the discipline for graduate students. Provides a comprehensive, up-to-date account of the field Covers computational methods as well as the underlying physics Serves as an ideal reference book for researchers and a rigorous yet accessible textbook for graduate students An online illustration package is available to professors at press.princeton.edu
Author: Carl J. Hansen
Publisher: Springer Science & Business Media
ISBN: 1468402145
Category : Science
Languages : en
Pages : 453
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Book Description
That trees should have been cut down to provide paper for this book was an ecological afIront. From a book review. - Anthony Blond (in the Spectator, 1983) The first modern text on our subject, Structure and Evolution of the Stars, was published over thirty years ago. In it, Martin Schwarzschild described numerical experiments that successfully reproduced most of the observed properties of the majority of stars seen in the sky. He also set the standard for a lucid description of the physics of stellar interiors. Ten years later, in 1968, John P. Cox's tw~volume monograph Principles of Stellar Structure appeared, as did the more specialized text Principles of Stellar Evolution and Nuc1eosynthesis by Donald D. Clayton-and what a difference ten years had made. The field had matured into the basic form that it remains today. The past twenty-plus years have seen this branch of astrophysics flourish and develop into a fundamental pillar of modern astrophysics that addresses an enormous variety of phenomena. In view of this it might seem foolish to offer another text of finite length and expect it to cover any more than a fraction of what should be discussed to make it a thorough and self-contained reference. Well, it doesn't. Our specific aim is to introduce only the fundamentals of stellar astrophysics. You will find little reference here to black holes, millisecond pulsars, and other "sexy" objects.
Author: Ivan Hubený
Publisher:
ISBN:
Category : Science
Languages : en
Pages : 760
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Book Description
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 23
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Book Description
The monochromatic opacity, [kappa]{sub v}, quantifies the property of a material to remove energy of frequency v from a radiation field. A harmonic average of [kappa]{sub v}, known as the Rosseland mean, [kappa]{sub R}, is frequently used to simplify the calculation of energy transport in stars. The term ''opacity'' is commonly understood to refer to [kappa]{sub R}. Opacity plays an important role in stellar modeling because for most stars radiation is the primary mechanism for transporting energy from the nuclear burning region in the core to the surface. Depending on the mass, convection and electron thermal conduction can also be important modes of stellar energy transport. The efficiency of energy transport is related to the temperature gradient, which is directly proportional to the mean radiative opacity in radiation dominated regions. When the radiative opacity is large, convection can become the more efficient energy transport mechanism. Electron conductive opacity, the resistance of matter to thermal conduction, is inversely proportional to electron thermal conductivity. Thermal conduction becomes the dominant mode of energy transport at high density and low temperature.
Author: Lucio Crivellari
Publisher: Cambridge University Press
ISBN: 1108603092
Category : Science
Languages : en
Pages : 251
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Book Description
Radiative transfer is essential for obtaining information from the spectra of astrophysical objects. This volume provides an overview of the physical and mathematical background of radiative transfer, and its applications to stellar and planetary atmospheres. It covers the phenomenology and physics of early-type and late-type stars, as well as ultra-cool dwarf stars and extrasolar planets. Importantly, it provides a bridge between classical radiative transfer and stellar atmosphere modelling and novel approaches, from both theoretical and computational standpoints. With new fields of application and a dramatic improvement in both observational and computational facilities, it also discusses the future outlook for the field. Chapters are written by eminent researchers from across the astronomical disciplines where radiative transfer is employed. Using the most recent observations, this is a go-to resource for graduate students and researchers in astrophysics.
Author: James E. Pringle
Publisher: Cambridge University Press
ISBN: 1139464442
Category : Science
Languages : en
Pages : 217
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Book Description
Almost all conventional matter in the Universe is fluid, and fluid dynamics plays a crucial role in astrophysics. This graduate textbook, first published in 2007, provides a basic understanding of the fluid dynamical processes relevant to astrophysics. The mathematics used to describe these processes is simplified to bring out the underlying physics. The authors cover many topics, including wave propagation, shocks, spherical flows, stellar oscillations, the instabilities caused by effects such as magnetic fields, thermal driving, gravity, shear flows, and the basic concepts of compressible fluid dynamics and magnetohydrodynamics. The authors are Directors of the UK Astrophysical Fluids Facility (UKAFF) at the University of Leicester, and editors of the Cambridge Astrophysics Series. This book has been developed from a course in astrophysical fluid dynamics taught at the University of Cambridge. It is suitable for graduate students in astrophysics, physics and applied mathematics, and requires only a basic familiarity with fluid dynamics.
Author: Rudolf Kippenhahn
Publisher: Springer Science & Business Media
ISBN: 3642615236
Category : Science
Languages : en
Pages : 480
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Book Description
A complete and comprehensive treatment of the physics of the stellar interior and the underlying fundamental processes and parameters. The text presents an overview of the models developed to explain the stability, dynamics and evolution of the stars, and great care is taken to detail the various stages in a star's life. The authors have succeeded in producing a unique text based on their own pioneering work in stellar modeling. Since its publication, this textbook has come to be considered a classic by both readers and teachers in astrophysics. This study edition is intended for students in astronomy and physics alike.
Author: G. CHABRIER (Ed)
Publisher: Cambridge University Press
ISBN: 9780521472609
Category : Science
Languages : en
Pages : 644
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Book Description
A unique review of our understanding of dense ionised matter in astrophysical contexts - essential reading for graduate students and researchers.
