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Author: Riwaj Pokhrel Publisher: ISBN: Category : Languages : en Pages :
Book Description
In this dissertation, I explore fragmentation physics in multiple scales in nearby molecular clouds and discuss some implications of fragmentation for cloud structure formation and star formation, primarily by analyzing multi-wavelength observations of dust emission. First, I tested the complete thermal and combined thermal and nonthermal support mechanisms that balance gravitational contraction at multiple scales in the Perseus molecular cloud. I found that the observed multiscale structures in Perseus are consistent with an inefficient thermal Jeans fragmentation, where the Jeans efficiency increases from the largest scale ($\gtrsim$10s of pc) to the smallest scale ($\sim$10s of AU). Next, I studied the effect of the formation of dense self-gravitating structures and star formation on the gas distribution in terms of its column density distribution function (N-PDF). I found that the evolutionary effect of clouds has corresponding changes on the N-PDF functional form, with a lognormal shape in diffuse regions that have negligible star formation, a lognormal and two power-laws in denser regions with moderate star formation, and a lognormal and one power-law in the densest regions with highly efficient clustered star formation. Finally, I explored the variations of star and gas surface densities in twelve molecular clouds using various techniques. I found that the stellar mass surface density of the recently formed stars varies as the square of the gas mass surface density in all twelve clouds. Also, I do not find any evidence of a column density threshold for efficient star formation.
Author: Riwaj Pokhrel Publisher: ISBN: Category : Languages : en Pages :
Book Description
In this dissertation, I explore fragmentation physics in multiple scales in nearby molecular clouds and discuss some implications of fragmentation for cloud structure formation and star formation, primarily by analyzing multi-wavelength observations of dust emission. First, I tested the complete thermal and combined thermal and nonthermal support mechanisms that balance gravitational contraction at multiple scales in the Perseus molecular cloud. I found that the observed multiscale structures in Perseus are consistent with an inefficient thermal Jeans fragmentation, where the Jeans efficiency increases from the largest scale ($\gtrsim$10s of pc) to the smallest scale ($\sim$10s of AU). Next, I studied the effect of the formation of dense self-gravitating structures and star formation on the gas distribution in terms of its column density distribution function (N-PDF). I found that the evolutionary effect of clouds has corresponding changes on the N-PDF functional form, with a lognormal shape in diffuse regions that have negligible star formation, a lognormal and two power-laws in denser regions with moderate star formation, and a lognormal and one power-law in the densest regions with highly efficient clustered star formation. Finally, I explored the variations of star and gas surface densities in twelve molecular clouds using various techniques. I found that the stellar mass surface density of the recently formed stars varies as the square of the gas mass surface density in all twelve clouds. Also, I do not find any evidence of a column density threshold for efficient star formation.
Author: E. Falgarone Publisher: Springer Science & Business Media ISBN: 9401133840 Category : Science Languages : en Pages : 557
Book Description
A few years ago, a motivation for organizing one more IAU Symposium on star for mation in Grenoble, was the anticipated completion of the IRAM interferometer on the Plateau de Bures, close to Grenoble. This choice was also a sort of late celebration of the genius of Joseph Fourier, born in Grenoble, whose work is the very fondation of in terferometry. At the time when we finally announced the advent of this conference, the first reactions we got from the community were expressions of saturation and even reject, the Symposium being unfortunately scheduled almost simultaneously as two other major meetings on closely related topics, and sponsored by different organizations. A wave of disappointment then reached the organizers. Some of us were enthusiastic enough to help the others overcome their discouragement. Let them be thanked here. There was, indeed, a deeper motivation for organizing this conference. It was to trigger the meeting and communication of physicists and astrophysicists since many of the difficulties met now in understanding the physics of the interstellar medium and its evolution toward star formation are common to several, if not most, other fields of physics. They are assigned to one origin: complexity.
Author: Leire Beitia Antero Publisher: ISBN: Category : Languages : en Pages :
Book Description
Star formation takes place inside cold, dense clouds of molecular material (molecularclouds) that experience a hierarchical fragmentation process. Inside these clouds the material organises itself in lamentary structures, with a density increasing at smaller scales where stars are eventually formed. The evolution ofthese clouds is aected by the injection of energy into the system. It is now widely accepted that magnetohydrodynamic turbulence contributes to sustain a molecular cloud against collapse and in consequence, directly inuences the star formation eciency. Magnetic elds, therefore, are a fundamental shaping agent of molecular clouds. The most external layers of these clouds, the so-called molecular cloud envelopes, are partially ionised due to their exposure to the ambient radiation field and hence are eectively coupled to the magnetic field. This coupling favours the propagation of hydromagnetic waves inside the clouds, increasing the turbulent state of the gas...
Author: Steven W. Stahler Publisher: John Wiley & Sons ISBN: 3527618686 Category : Science Languages : en Pages : 865
Book Description
This book is a comprehensive treatment of star formation, one of the most active fields of modern astronomy. The reader is guided through the subject in a logically compelling manner. Starting from a general description of stars and interstellar clouds, the authors delineate the earliest phases of stellar evolution. They discuss formation activity not only in the Milky Way, but also in other galaxies, both now and in the remote past. Theory and observation are thoroughly integrated, with the aid of numerous figures and images. In summary, this volume is an invaluable resource, both as a text for physics and astronomy graduate students, and as a reference for professional scientists.
Author: Steven Stahler Publisher: Springer ISBN: 3319228013 Category : Science Languages : en Pages : 205
Book Description
All stars are born in groups. The origin of these groups has long been a key question in astronomy, one that interests researchers in star formation, the interstellar medium, and cosmology. This volume summarizes current progress in the field, and includes contributions from both theorists and observers. Star clusters appear with a wide range of properties, and are born in a variety of physical conditions. Yet the key question remains: How do diffuse clouds of gas condense into the collections of luminous objects we call stars? This book will benefit graduate students, newcomers to the field, and also experienced scientists seeking a convenient reference.
Author: Joseph A. Nuth Publisher: ISBN: Category : Planetary theory Languages : en Pages : 124
Book Description
Topics addressed include: interstellar chemistry and primitive bodies; astronomical measurements and nebula models; solar nebula models and meteorite; and planetary accumulation and evolution.
Author: Ana I. Gómez de Castro Publisher: Springer ISBN: 9789048166022 Category : Science Languages : en Pages : 0
Book Description
Magnetic Fields play a key role in the physics of star formation on all scales: from the formation of the large complexes of molecular clouds to the formation of solar-like planetary systems. The plasma physics involved is non-linear and very complex, which requires the development of large numerical codes. An additional difficulty is that the detection and study of magnetic fields is not easy from an observational point of view, and therefore theoretical models cannot easily be constrained. In the week from April 21st to 25th in 2003, a meeting was held on the Campus of the Universidad Complutense de Madrid (Spain) to join theoretical and observational efforts to address these issues. The objective was to define a set of relevant problems for the physics of star formation that can be properly addressed with the current or near-future instruments. This book summarizes the results of this intensive week of work. The book is written in a comprehensive manner and reviews our current knowledge of the subject. It also represents an updated account of the ideas and thoughts of the scientists working in the field of Star Formation. The contributions are presented in six chapters which correspond to the six fundamental issues (sessions) on which the discussion was focused during the workshop: the physics of turbulence in the Interstellar Medium (ISM), the formation of structure in the ISM, the formation of stars within dense cores of molecular gas, the physics of accretion disks, the physics of outflows and their interaction with the ISM, and the interaction between the stellar magnetosphere and accretion disk. Each chapter starts with a comprehensive summary written by one of the editors, which includes input from the contributions as well as the editor's own thoughts on the subject. For all these reasons the book is well-suited as a primer to introduce graduate students in the richness of this field of research.
Author: Roberto Capuzzo-Dolcetta Publisher: Springer Science & Business Media ISBN: 9400906056 Category : Science Languages : en Pages : 462
Book Description
Recent years have witnessed the expansion and multiplication of the observations of star formation and fragmentation accompanied by a consequent growth in the study of the underlying physical processes, the chemistry, the sites, the times, etc. Moreover, recent studies have shown that the formation of stars is likely to share many features with the formation of other self-gravitating objects. The present volume, therefore, discusses the formation of such objects in a systematic and comparative manner.
Author: Riwaj Pokhrel
Author: Riwaj Pokhrel
Author: Ke Wang
Author: E. Falgarone
Author: Leire Beitia Antero
Author: Steven W. Stahler
Author: Steven Stahler
Author: Joseph A. Nuth
Author: Ana I. Gómez de Castro
Author: 
Author: Roberto Capuzzo-Dolcetta