Modelling Feedback in Turbulent Molecular Cloud Cores PDF Download

Author: Douglas F.A. Boyd
Publisher:
ISBN:
Category : Astronomy
Languages : en
Pages : 168

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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 38

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Book Description
In this study we investigate the formation and properties of prestellar and protostellar cores using hydrodynamic, self-gravitating Adaptive Mesh Refinement simulations, comparing the cases where turbulence is continually driven and where it is allowed to decay. We model observations of these cores in the C18O(2 2!1), NH3(1,1), and N2H (1 2!0) lines, and from the simulated observations we measure the linewidths of individual cores, the linewidths of the surrounding gas, and the motions of the cores relative to one another. Some of these distributions are significantly different in the driven and decaying runs, making them potential diagnostics for determining whether the turbulence in observed star-forming clouds is driven or decaying. Comparing our simulations with observed cores in the Perseus and [rho] Ophiuchus clouds shows reasonably good agreement between the observed and simulated core-to-core velocity dispersions for both the driven and decaying cases. However, we find that the linewidths through protostellar cores in both simulations are too large compared to the observations. The disagreement is noticeably worse for the decaying simulation, in which cores show highly supersonic infall signatures in their centers that decrease toward their edges, a pattern not seen in the observed regions. This result gives some support to the use of driven turbulence for modeling regions of star formation, but reaching a firm conclusion on the relative merits of driven or decaying turbulence will require more complete data on a larger sample of clouds as well as simulations that include magnetic fields, outflows, and thermal feedback from the protostars.

Author: José Franco
Publisher: Cambridge University Press
ISBN: 9780521651318
Category : Science
Languages : en
Pages : 304

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This timely volume presents a series of review articles covering every aspect of interstellar turbulence--from accretion disks, molecular clouds, atomic and ionized media, through to spiral galaxies - based on a major international conference held in Mexico City.With advances in observational techniques and the development of more efficient computer codes and faster computers, research in this area has made spectacular progress in recent years. This book provides a comprehensive overview of the most important developments in observing and modelling turbulent flows in the cosmos. It provides graduate student and researchers with a state-of-the-art summary of observational, theoretical and computational research in interstellar turbulence.

Author: Jonathan J. Carroll-Nellenback
Publisher:
ISBN:
Category :
Languages : en
Pages : 124

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"Star formation occurs within complex assemblies of cold dense matter known as molecular clouds. The dynamics of these clouds involve a wide variety of physical processes over a wide range in length scales, making numerical modeling of these clouds a challenging and interesting problem. On the largest scales (10-100 parsec) there is a constant battle between forces acting to support or unbind the cloud (stellar feedback from super-novae and HII regions, magnetic fields, turbulence, and shear), and those attempting to compress the cloud (thermal and/or ram pressure from the interstellar medium (ISM) and gravity). On smaller scales the same turbulent motions that support the cloud as a whole can produce dense filamentary regions within the cloud that can undergo local collapse. On intermediate scales (1 pc), feedback in the form of winds and outflows can disrupt density structures and provide turbulent energy to reduce the rate of star formation. The large dynamical range requires use of sophisticated codes such as AstroBEAR. The high degree of resolution required as well as the increase in the sheer number of central processing units (CPUs) available to perform calculations requires codes that achieve new levels of efficient parallelization and memory management. We have employed new techniques to achieve both of these goals in our modeling of various aspects of turbulence in molecular clouds including turbulence driven by stellar feedback within the cloud, turbulence driven externally, and turbulence driven by the interaction of inhomogeneous streams of gas within the ISM"--Page iv.

Author: Charles Edward Hansen
Publisher:
ISBN:
Category :
Languages : en
Pages : 186

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I investigate the decay and regeneration of turbulence in molecular clouds and the resulting star formation in those clouds in the presence of protostellar feedback. Studies of turbulence generally only consider isotropic turbulence, while the turbulence in molecular clouds may be anisotropic. I perform a series of simulations of anisotropic turbulence and measure its decay rate. I find that anisotropic turbulence decays slower than isotropic turbulence. When I break the velocity dispersion into isotropic and anisotropic components, I find the decay time is the crossing time of the isotropic component, which can be much slower than the total velocity dispersion. As part of this study, I present a measure of anisotropy that can be calculated in observations of molecular clouds. I also investigate the effects of compression on turbulence. This is motivated by the need to replenish turbulent energy. Using a series of simulations of contracting turbulence, I find that turbulence behaves as a monatomic ideal gas under isotropic compression. I also find that compression in a single direction imparts energy to that direction, but does not transfer that energy to the other two directions. Finally, I perform a series of high resolution star formation simulations with adaptive mesh refinement (AMR) including hydrodynamics, gravity, radiation, protostellar outflows and protostellar luminosity. The simulations provide a self-consistent story of star formation, all while matching observations. The matched observations include the masses of both stars and prestellar cores, the clustering of cores and the luminosity function of protostars. In this story of star formation, cores form on the Jeans length of the host cloud. Each core forms a central star or binary, but also fragments repeatedly down 0.05 $M_{\odot}$ stars. The stellar radiation prevents fragmentation below this mass scale, but is not important on larger scales. The protostellar outflows eject 2/3 of the incoming mass, leaving 1/3 of the core mass for stars.

Author: Derek Ward-Thompson
Publisher: Frontiers Media SA
ISBN: 2889637727
Category :
Languages : en
Pages : 224

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Author: Bruce T. Draine
Publisher: Princeton University Press
ISBN: 1400839084
Category : Science
Languages : en
Pages : 560

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This is a comprehensive and richly illustrated textbook on the astrophysics of the interstellar and intergalactic medium--the gas and dust, as well as the electromagnetic radiation, cosmic rays, and magnetic and gravitational fields, present between the stars in a galaxy and also between galaxies themselves. Topics include radiative processes across the electromagnetic spectrum; radiative transfer; ionization; heating and cooling; astrochemistry; interstellar dust; fluid dynamics, including ionization fronts and shock waves; cosmic rays; distribution and evolution of the interstellar medium; and star formation. While it is assumed that the reader has a background in undergraduate-level physics, including some prior exposure to atomic and molecular physics, statistical mechanics, and electromagnetism, the first six chapters of the book include a review of the basic physics that is used in later chapters. This graduate-level textbook includes references for further reading, and serves as an invaluable resource for working astrophysicists. Essential textbook on the physics of the interstellar and intergalactic medium Based on a course taught by the author for more than twenty years at Princeton University Covers radiative processes, fluid dynamics, cosmic rays, astrochemistry, interstellar dust, and more Discusses the physical state and distribution of the ionized, atomic, and molecular phases of the interstellar medium Reviews diagnostics using emission and absorption lines Features color illustrations and detailed reference materials in appendices Instructor's manual with problems and solutions (available only to teachers)

Author: Brandt Gaches
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Star formation is the lynch pin that lies in between the scales of galaxy and planet formation. Observational studies of molecular clouds, the sites of star formation, primarly use molecular line emission, providing dynamical and chemical information. Two of the key parameters of astrochemical models are far-ultraviolet (FUV) flux and the cosmic ray ionization rate. We use analytic accretion histories to predict the bolometric and FUV luminosities of protostar clusters and compare different histories with observed bolometric luminosities. We find that the Tapered Turbulent Core model best represents the observed luminosities and their dispersion. We extend the models to calculate the cosmic ray spectrum of protons accelerated in protostellar accretion shocks. We find that protostars are able to accelerate cosmic rays up to 10 GeV. We predict increased ionization rates within protostellar cores and molecular clouds hosting over 100 protostars. Our model is able to explain the substantial ionization rate, over 1000 times the typical, observed towards the OMC-2 FIR 4 protocluster. We model the impact of the protostellar FUV and cosmic rays on the astrochemistry on the natal molecular cloud. We couple the chemistry to the cosmic ray attenuation to solve the cosmic ray attenuation self-consistently. We find the inclusion of the embedded feedback significantly changes the Carbon chemistry and the CO-to-H2 conversion factor. High-density, optically-thin tracers such as ammonia are noticeably affected. The inclusion of embedded protostellar feedback alters the chemistry throughout molecular clouds, coupling the physics ongoing on the smallest scales of star formation to molecular cloud scale. Our results show that astrochemical modeling should account for ongoing star formation to correctly account for embedded FUV radiation and cosmic rays.

Author: Bo Reipurth
Publisher: University of Arizona Press
ISBN: 9780816526543
Category : Science
Languages : en
Pages : 994

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Book Description
'Protostars and Planets V' builds on the latest results from recent advances in ground and space-based astronomy and in numerical computing techniques to offer the most detailed and up-to-date picture of star and planet formation - including the formation and early evolution of our own solar system.

Author: Henrik Beuther
Publisher: University of Arizona Press
ISBN: 0816598762
Category : Science
Languages : en
Pages : 945

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Book Description
The revolutionary discovery of thousands of confirmed and candidate planets beyond the solar system brings forth the most fundamental question: How do planets and their host stars form and evolve? Protostars and Planets VI brings together more than 250 contributing authors at the forefront of their field, conveying the latest results in this research area and establishing a new foundation for advancing our understanding of stellar and planetary formation. Continuing the tradition of the Protostars and Planets series, this latest volume uniquely integrates the cross-disciplinary aspects of this broad field. Covering an extremely wide range of scales, from the formation of large clouds in our Milky Way galaxy down to small chondrules in our solar system, Protostars and Planets VI takes an encompassing view with the goal of not only highlighting what we know but, most importantly, emphasizing the frontiers of what we do not know. As a vehicle for propelling forward new discoveries on stars, planets, and their origins, this latest volume in the Space Science Series is an indispensable resource for both current scientists and new students in astronomy, astrophysics, planetary science, and the study of meteorites.