Evolution Of Brown Dwarfs
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Evolution Of Brown Dwarfs
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Author : Sen-Ben R. Liao
language : en
Publisher:
Release Date : 1989
Evolution Of Brown Dwarfs written by Sen-Ben R. Liao and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1989 with categories.
50 Years Of Brown Dwarfs
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Author : Viki Joergens
language : en
Publisher: Springer Science & Business Media
Release Date : 2013-11-27
50 Years Of Brown Dwarfs written by Viki Joergens and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013-11-27 with Science categories.
The years 2012/2013 mark the 50th anniversary of the theoretical prediction that Brown Dwarfs, i.e. degenerate objects which are just not massive enough to sustain stable hydrogen fusion, exist. Some 20 years after their discovery, how Brown Dwarfs form is still one of the main open questions in the theory of star formation. In this volume, the pioneers of Brown Dwarf research review the history of the theoretical prediction and the subsequent discovery of Brown Dwarfs. After an introduction, written by Viki Joergens, reviewing Shiv Kumar's theoretical prediction of the existence of brown dwarfs, Takenori Nakano reviews his and Hayashi's calculation of the Hydrogen Burning Minimum Mass. Both predictions happened in the early 1960s. Jill Tarter then writes on the introduction of the term 'Brown Dwarf', before Ben Oppenheimer, Rafael Rebolo and Gibor Basri describe their first discovery of Brown Dwarfs in the 1990s. Lastly, Michael Cushing and Isabelle Baraffe describe the development of the field to the current state of the art. While the book is mainly aimed at the Brown Dwarf research community, the description of the pioneering period in a scientific field will attract general readers interested in astronomy as well.
Evolutionary Scenario For Low Mass Stars And Substellar Brown Dwarfs
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Author : Guy S. Stringfellow
language : en
Publisher:
Release Date : 1989
Evolutionary Scenario For Low Mass Stars And Substellar Brown Dwarfs written by Guy S. Stringfellow and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1989 with Brown dwarf stars categories.
Brown Dwarf Companions To Young Solar An
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Author : Stanimir Metchev
language : en
Publisher: Universal-Publishers
Release Date : 2006-02
Brown Dwarf Companions To Young Solar An written by Stanimir Metchev and has been published by Universal-Publishers this book supported file pdf, txt, epub, kindle and other format this book has been release on 2006-02 with Science categories.
We present results from an adaptive optics survey conducted with the Palomar and Keck telescopes over 3 years, which measured the frequency of stellar and sub-stellar companions to Sun-like stars. The survey sample contains 266 stars in the 3-10000 million year age range at heliocentric distances between 8 and 200 parsecs and with spectral types between F5-K5. A sub-sample of 101 stars, between 3-500 million years old, were observed in deep exposures with a coronagraph to search for faint sub-stellar companions. A total of 288 candidate companions were discovered around the sample stars, which were re-imaged at subsequent epochs to determine physical association with the candidate host stars by checking for common proper motion. Benefitting from a highly accurate astrometric calibration of the observations, we were able to successfully apply the common proper motion test in the majority of the cases, including stars with proper motions as small as 20 milli-arcseconds/year. The results from the survey include the discovery of three new brown dwarf companions (HD 49197B, HD 203030B, and ScoPMS 214B), 43 new stellar binaries, and a triple system. The physical association of an additional, a priori-suspected, candidate sub-stellar companion to the star HII 1348 is astrometrically confirmed. The newly-discovered and confirmed young brown dwarf companions span a range of spectral types between M5 and T0.5, and will be of prime significance for constraining evolutionary models of young brown dwarfs and extra-solar planets. Based on the 3 new detections of sub-stellar companions in the 101 star sub-sample and following a careful estimate of the survey incompleteness, a Bayesian statistical analysis shows that the frequency of 0.012-0.072 solar-mass brown dwarfs in 30-1600 AU orbits around young solar analogs is 6.8% (-4.9%, +8.3%; 2-sigma limits). While this is a factor of 3 lower than the frequency of stellar companions to G-dwarfs in the same orbital range, it is significantly higher than the frequency of brown dwarfs in 0-3 AU orbits discovered through precision radial velocity surveys. It is also fully consistent with the observed frequency of 0-3 AU extra-solar planets. Thus, the result demonstrates that the radial-velocity "brown dwarf desert" does not extend to wide separations, contrary to previous belief.
Brown Dwarfs And Ukidss
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Author : David Edwin Alexander Baker
language : en
Publisher:
Release Date : 2011
Brown Dwarfs And Ukidss written by David Edwin Alexander Baker and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2011 with categories.
In this thesis I present the work of two studies into the population of low-mass stars and brown dwarfs within the open galactic clusters of Praesepe and Blanco 1 using optical and infrared photometry. Observing these objects within clusters is of great importance as their known ages and distances allow for comparisons to be made between the observed results and those predicted from theoretical formation and evolutionary models, whilst expanding our understanding of the initial mass function. Following an introduction to the formation, evolution and observational history of brown dwarfs in Chapter 2 an overview of the principle data reduction processes and instruments used in this thesis is given in Chapter 3. Chapter 4 presents the result of the survey carried out in Praesepe using archival 2MASS, SDSS and UKIDSS data in a range of filters. Proper motion information is combined with colour magnitude cuts to select out and classify objects that are considered to be cluster members. Over 280 members have been identified with a cluster mass function that is consistent with the values presented for other clusters found. This mass function is in disagreement with previous values found for Praesepe. Chapter 5 presents the results of a follow up J band survey using WFCAM to theCFHT12k I and z survey of Moraux et al. (2007). The data reduction and membership selection procedure are discussed with 27 low-mass objects found to be members. Chapter 6 in contrast to the previous chapters presents a study not of brown dwarfs but of a suspected main-sequence, magnetic white-dwarf binary system found during an archival search of the UKIDSS DR3 database for objects with unusual Y band colours. The evidence for this system being a Polar is presented along with a discussion as to the assumed system properties. Follow up observations using the IAC-80 telescope, UKIRT and the SWIFT satellite are also presented. Finally in Chapter 7 I summarise the results from each chapter and identify areas of future work.
The Formation And Early Evolution Of Stars
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Author : Norbert S. Schulz
language : en
Publisher: Springer Science & Business Media
Release Date : 2012-05-24
The Formation And Early Evolution Of Stars written by Norbert S. Schulz and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2012-05-24 with Science categories.
Starburst regions in nearby and distant galaxies have a profound impact on our understanding of the early universe. This new, substantially updated and extended edition of Norbert Schulz’s unique book "From Dust to Stars" describes complex physical processes involved in the creation and early evolution of stars. It illustrates how these processes reveal themselves from radio wavelengths to high energy X-rays and gamma–rays, with special reference towards high energy signatures. Several sections devoted to key analysis techniques demonstrate how modern research in this field is pursued and new chapters are introduced on massive star formation, proto-planetary disks and observations of young exoplanets. Recent advances and contemporary research on the theory of star formation are explained, as are new observations, specifically from the three great observatories of the Spitzer Space Telescope, the Hubble Space Telescope and the Chandra X-Ray Observatory which all now operate at the same time and make high resolution space based observing in its prime. As indicated by the new title two new chapters have been included on proto-planetary disks and young exoplanets. Many more colour images illustrate attractive old and new topics that have evolved in recent years. The author gives updates in theory, fragmentation, dust, and circumstellar disks and emphasizes and strengthens the targeting of graduate students and young researchers, focusing more on computational approaches in this edition.
The Theory Of The Formation Of Brown Dwarfs
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Author :
language : en
Publisher:
Release Date : 2005
The Theory Of The Formation Of Brown Dwarfs written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2005 with categories.
We investigate the dynamical decay of non-hierarchical accreting triple systems and its implications on the ejection model as Brown Dwarf formation scenario. A modified chain-regularization scheme is used to integrate the equations of motion, that also allows for mass changes over time as well as for momentum transfer from the accreted gas mass onto the bodies. We integrate an ensemble of triple systems within a certain volume with different accretion rates, assuming several prescriptions of how momentum is transferred onto the bodies. We follow their evolution until the systems have decayed. We find that the formation probability of Brown Dwarfs depends strongly on the assumed momentum transfer which is related to the motion of the gas. Due to ongoing accretion and consequent shrinkage of the systems, the median escape velocity is increased by a factor of 2 and the binary separations are decreased by a factor of 5 compared with non-accreting systems. Furthermore, the obtained semi-major axis distribution drops off sharply to either side of the median, which is also supported by observations. However, the disks around the ejected Brown Dwarfs seem to have too low accretion rates and masses to account for many of the observed disks in typical low-mass star-forming regions. We conclude that accretion of gas and the kinematic properties of the accreted gas during dynamical interactions strongly influence the abundance as well as the dynamical properties of Brown Dwarfs and, that the ejection scenario seems to be a promising scenario to produce both, very close Brown Dwarf binaries as well as single Brown Dwarfs, whereas it seems less likely to find very long-lived accretion disks around them.
The Future Of Protoplanetary Disk Models
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Author : Aaron James Greenwood
language : en
Publisher:
Release Date : 2018
The Future Of Protoplanetary Disk Models written by Aaron James Greenwood and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018 with categories.
Stars Stellar Evolution
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Author : Klaas de Boer
language : fr
Publisher: EDP Sciences
Release Date : 2012-12-17T00:00:00+01:00
Stars Stellar Evolution written by Klaas de Boer and has been published by EDP Sciences this book supported file pdf, txt, epub, kindle and other format this book has been release on 2012-12-17T00:00:00+01:00 with Science categories.
The diverse forms that stars assume in the course of their lives can all be derived from the initial conditions : the mass and the original chemical composition. In this textbook Stars and Stellar Evolution the basic concepts of stellar structure and the main roads of stellar evolution are described. First, the observable parameters are presented, which are based on the radiation emerging from a stellar atmosphere. Then the basic physics is described, such as the physics of gases, radiation transport, and nuclear processes, followed by essential aspects of modelling the structure of stars. After a chapter on star formation, the various steps in the evolution of stars are presented. This leads us to brown dwarfs, to the way a star changes into the red-giant state and numerous other stages of evolution and ultimately to the stellar ashes such as white dwarfs, supernovae and neutron stars. Stellar winds, stellar rotation and convection all influence the way a star evolves. The evolution of binary stars is included by using several canonical examples in which interactive processes lead to X-ray binaries and supernovae of type Ia. Finally, the consequences of the study of stellar evolution are tied to observed mass and luminosity functions and to the overall evolution of matter in the universe. The authors aim at reaching an understanding of stars and their evolution by both graduate students and astronomers who are not themselves investigating stars. To that end, numerous graphs and sketches, among which the Hertzsprung-Russell diagram is the dominant one, help trace the ways of stellar evolution. Ample references to specialised review articles as well as to relevant research papers are included.
From Dust To Stars
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Author : Norbert S. Schulz
language : en
Publisher: Springer Science & Business Media
Release Date : 2007-03-06
From Dust To Stars written by Norbert S. Schulz and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2007-03-06 with Science categories.
Studies of stellar formation in galaxies have a profound impact on our understanding of the present and the early universe. The book describes complex physical processes involved in the creation of stars and during their young lives. It illustrates how these processes reveal themselves from radio wavelengths to high energy X-rays and gamma -rays, with special reference towards high energy signatures. Several sections devoted to key analysis techniques demonstrate how modern research in this field is pursued.