As shown from the fig our photometric observations almost covered the whole period of variations of DQ Her. We see that light reprocessed through the accretion disk because we see the disk edge-on, and the white dwarf itself is obscured.
Different characteristic features of DQ Her variations, i. In both figures, the KAO photometry is in red. Where M a , R a are the mass and radius of the accreting star, L acc is the accretion luminosity, and G is the gravitational constant. We report the results of the photometric and spectroscopic behavior of DQ Her.
The main results for the system can be summarized as:. Photometry of DQ Her revealed that the system is an eclipsing binary with high inclination deg. The light variation reveal very deep primary minimum where, main sequence component lie in front of the white dwarf The intermediate Polar system DQ Herculis, in which the white dwarf is gravitationally stripped the matter from the main-sequence companion star and forms an accretion disk around the white dwarf and the inner disk region is truncated by the magnetic field of the white dwarf.
Disk material passes through the curtains and then accretes onto the white dwarf near one of its magnetic poles. One periodicity is related to the orbital period of the binary star system. A second periodic signal originates from the rotation of the white dwarf spinning on its axis and it is shorter than the orbital period.
The observational characteristic that clearly defines this system is the existence of more than one overlap period which appear in general as irregular variables. The physical cause of optical spin period oscillations may be attributed to the changing viewing aspect of the accretion curtain as it converges near the white dwarf. There are variations in the ultraviolet luminosities and the mass accretion rates.
Edward M. Sion - Wikiwand
There are modulations in line fluxes for all studied emission lines C IV and He II , we attributed these variations to the variations of the rate of mass transfer from the secondary star to the white dwarf leading to variation in temperature and consequently to the variations in the intensities of emission lines.
The variations in both ultraviolet luminosities and the mass accretion rates in this system can be interpreted in terms of the accretion curtain model. The main results for the system can be summarized as: Photometry of DQ Her revealed that the system is an eclipsing binary with high inclination deg. Examples are Type Ia supernovae i.
As an assisting guide to the reader, we have included, by invitation, comprehensive review articles in each of the four major areas of the book, white dwarf supernovae, cosmology, accretion physics and galactic structure. The reviews include introductory material that they build upon. The book is suitable and most useful to advanced undergraduates, graduate students and scientific professionals e.
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Sion, Professor of Astronomy and Astrophysics, Villanova University, Former Scientific Editor, The Astrophysical Journal, author or co-author of over scientific publications on white dwarfs and cataclysmic variable stars, co-author of the Catalogue of Spectroscopically Identified White Dwarfs. Stephane Vennes, Research Astronomer, Johns Hopkins University, Lecturer, Australian national University, leading expert on the physics of diffusion, radiative forces, and accretion onto white dwarfs, and specialist on space ultraviolet studies of white dwarf stars.
Harry L. Shipman, Annie Jump Cannon Professor of Astronomy, University of Delaware, Distinguished Educator Medal, the National Science Foundation, author or co-author of over scientific publications on white dwarfs and author of Black Holes and the Infinite Universe and Introductory Astronomy, leading expert on white dwarf stars and science education.
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Table of Contents Section I. Halo White Dwarfs and Galactic Structure. Number counts of white dwarfs: the impact of GAIA. Dark halo baryons not in ancient white dwarfs? White Dwarfs in Globular Clusters. Planetary Nebulae and the Galactic Bulge. Section II. The Legacy of J. Kapteyn Piet C. History of Oriental Astronomy S.
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Gravity, Particles, and Astrophysics Paul S. Kristian Birkeland Alv Egeland. Back cover copy This book guides readers astronomers, physicists, and university students through central questions of Practical Cosmology, a term used by the late Allan Sandage to denote the modern scientific endeavor to find the cosmological model best describing the universe of galaxies, its geometry, size, age, and matter composition. These highlighted items are: - Idiosyncratic features of the "cosmic laboratory" - Malmquist bias in the determination of cosmic distances - Theory of gravitation as a cornerstone of cosmological models - Crucial tests for checking the reality of space expansion - Methods of analyzing the structures of the universe as mapped by galaxies - Usefulness of fractals as a model to describe the large-scale structure - New cosmological physics inherent in the Friedmann world model show more.
Table of contents Chapter 1 The golden age of cosmological physics. About Yurij Baryshev Dr. Yurij Baryshev b.
lansiberruck.tk Petersburg University, Russia. He has done research in various fields of extragalactic astronomy and cosmology, where his main research interest is relativistic astrophysics including cosmology and gravity physics. He has investigated Einstein's and Feynman's approaches to gravitation, active galactic nuclei, quasars, gravitational radiation, gravitational lensing by dark matter, and crucial cosmological tests.
He has also studied the implications for cosmology of the recent discovery of the dark energy component and the fractal structure of the luminous matter distribution. He has co-authored with P. Pekka Teerikorpi b. He has done research in various fields of Galactic and extragalactic astronomy and practical cosmology, with special interest in the selection effects and biases influencing the determination of the cosmic distance scale and the value of the Hubble constant.
He has also made excursions to the Milky Way the rotation curve, interstellar dust , the realm of active galactic nuclei and the problem of the local detection of dark energy. He has co-authored with Yu. Baryshev the book on the history of the Cosmological Principle Discovery of Cosmic Fractals World Scientific and has recently written, together with a few other astronomers and exobiologists the book The Evolving Universe and the Origin of Life - The Search for our Cosmic Roots Springer , telling about the history and spirit of our science.