Download or read book Development and Testing of a New Method for Velocity selecting White Dwarfs from Gaia by Galactic Population written by Joseph Hammill and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The detailed processes by which spiral galaxies form remains an open question in modern cosmology. Observations of the current configuration of spiral galaxies including the Milky Way reveal thin and thick disk and halo populations which must all be accounted for in formation theories and likely have distinct ages. Using the Milky Way as an example to probe this question, we are studying the formation history of these structures.
Download or read book Population Synthesis Studies of the White Dwarfs of the Galactic Disk and Halo written by Elena-Ruxandra Cojocaru and published by . This book was released on 2017 with total page 157 pages. Available in PDF, EPUB and Kindle. Book excerpt: As the evolutionary end-point of most main-sequence stars, white dwarfs can be used to infer important properties concerning the formation and evolution of the different Galactic stellar populations. Population synthesis methods, when correlated with the excellent quality of modern white dwarf cooling tracks, can prove to be a powerful tool for further exploring the information offered by observed samples of white dwarfs. Possible applications may include estimating the age and history of stellar populations, measuring the local stellar formation rate and stellar density, constraining the local content of baryonic matter, examining intrinsic aspects of single and binary stellar evolution and exploring different progenitor scenarios for type Ia supernovae. In this thesis we studied the white dwarf populations of the Galactic disk and halo and our work was focused on four main objectives. The first was to analyze the effects of stellar metallicity on the white dwarf luminosity function of the Galactic disk. We use our Monte Carlo population synthesis code to produce synthetic samples of white dwarfs which we later compare to two relatively large observational samples, from the Sloan Digital Sky Survey (SDSS) and SuperCosmos Sky Survey (SSS). For each of the two cases, we implement the corresponding observational selection criteria. We first explore the impact of varying the fraction of white dwarfs with hydrogen-deficient atmospheres and of using alternative sets of cooling tracks. We then test different age-metallicity relations, considering the impact of progenitor metallicity throughout the entire evolution of the star. Our second objective was to determine the luminosity, mass and cumulative age functions derived from a sample of disk white dwarfs identified by the LAMOST Sky Survey of the Galactic Anti-Center. We initially compute the observed functions and then the theoretical ones, according to series of initial assumptions, using our population synthesis code. We derive values for the local space density and formation rate of hydrogen-rich white dwarfs and analyze the possible causes behind the apparent excess of massive white dwarfs identified in the observed mass function. The next objective of this thesis was to revisit the halo white dwarf luminosity function, modeling the halo white dwarf population using a self-consistent prescription for very low metallicity progenitors. We pass the synthetic sample through a series of filters that reproduce the selection criteria employed in culling the observed sample of halo white dwarfs from the SSS. Given that for very low-metallicity progenitors residual hydrogen burning can become a significant source of energy, we test two different sets of cooling tracks, one that incorporates residual hydrogen burning and another where this phenomenon is artificially ignored. Finally, our last study consisted in modeling the sample of white dwarf-main sequence binaries in the Galactic disk. We compare our simulations to the largest and most recent catalog of white dwarf-main sequence binaries from the SDSS and we provide a detailed account of observational biases and errors. We use this sample to constrain several important inputs for binary formation and evolution, namely the initial mass ratio distribution and the common envelope efficiency parameter. To conclude, the work presented in this thesis testifies to the versatility of using white dwarf populations for constraining different properties of the Galactic disk and halo. The methodology described here can be used in future studies of this kind, with a myriad of new applications, especially given than in the near future a noticeable improvement in terms of the size and quality of observed white dwarf catalogs is expected.
Download or read book White Dwarfs and the Ages of Stellar Populations written by Steven Andrew De Gennaro and published by . This book was released on 2009 with total page 270 pages. Available in PDF, EPUB and Kindle. Book excerpt: Our group has developed a Bayesian modeling technique to determine the ages of stellar populations (in particular, open and globular clusters) using white dwarf (WD) cooling physics. As the theory of WD cooling is both simpler than, and essentially independent of, main sequence evolutionary theory, white dwarfs provide an independent measure of the ages of Galactic populations. We have developed a Bayesian technique that objectively incorporates our prior knowledge of stellar evolution, star cluster properties, and data quality estimates to derive posterior probability distributions for a cluster's age, metallicity, distance, and line-of-sight absorption, as well as the individual stellar parameters of mass, mass ratio (for unresolved binaries) and cluster membership probability. The key advantage of our Bayesian method is that we can calculate probability distributions for cluster and stellar parameters with reference only to known, quantifiable, objective, and repeatable quantities. In doing so, we also have more sensitivity to subtle changes in cluster isochrones than traditional "chi-by-eye'" cluster fitting methods. As a critical test of our Bayesian modeling technique, we apply it to Hyades UBV photometry, with membership priors based on proper motions and radial velocities, where available. We use secular parallaxes derived from Hipparcos proper motions via the moving cluster method to put all members of the Hyades at a common distance. Under the assumption of a particular set of WD cooling and atmosphere models, we estimate the age of the Hyades based on cooling white dwarfs to be 610 ± 110 Myr, consistent with the best prior analysis of the cluster main-sequence turn-off age (Perryman, et al. 1998). Since the faintest white dwarfs have most likely evaporated from the Hyades, prior work provided only a lower limit to the cluster's white dwarf age. Our result demonstrates the power of the bright white dwarf technique for deriving ages (Jeffery, et al. 2007) and further demonstrates complete age consistency between white dwarf cooling and main-sequence turn-off ages for seven out of seven clusters analyzed to date, ranging from 150 Myr to 4 Gyr. We then turn our attention to the white dwarf luminosity function. We use Sloan Digital Sky Survey (SDSS) data to create a white dwarf luminosity function with nearly an order of magnitude (3,358) more spectroscopically confirmed white dwarfs than any previous work. We determine the completeness of the SDSS spectroscopic white dwarf sample by comparing a proper-motion selected sample of WDs from SDSS imaging data with a large catalog of spectroscopically determined WDs. We derive a selection probability as a function of a single color (g-i) and apparent magnitude (g) that covers the range -1.0
Download or read book Structure and Dynamics of Elliptical Galaxies written by Tim de Zeeuw and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 589 pages. Available in PDF, EPUB and Kindle. Book excerpt: IAU Symposium 127 was held in Princeton on May 28-31, 1986, at the Institute for Advanced Study. There were 150 participants from 19 countries. This was the first IAU Symposium devoted exclusively to elliptical galaxies. The last decade has been a period of exceptionally rapid progress regard ing our understanding of elliptical galaxies, driven on the observational side by a wealth of new photometric and spectroscopic data, and on the theoretical side by the recognition that ellipticals are slowly rotating triaxial systems, instead of rotationally flattened bodies. The 30 invited speakers reviewed all aspects of this progress, its consequences, and the major outstanding problems. Nearly 80 poster contributions were displayed for the duration of the meeting. These contained many of the most recent developments. The first part of these Proceedings contains the written versions of the invited reviews and the summary, in the order of their presentation. The accompanying discussions are based on the written versions of questions and answers as handed in by the participants. The second part of this book is devoted to the poster contribu tions. They have been grouped in a thematic order, proceeding from morphology to theory. Indices of objects, subjects, and names are provided. Unfortunately, none of the invited participants from the USSR were able to attend the Symposium. The Proceedings include the written versions of the planned contributions by Popov and Polyachenko.
Download or read book Gravitational Dynamics written by Ofer Lahav and published by Cambridge University Press. This book was released on 1996-07-13 with total page 286 pages. Available in PDF, EPUB and Kindle. Book excerpt: Gravity plays a central role in the dynamics of all astrophysical systems - from stars to the Universe as a whole. This timely volume examines all aspects of gravitational dynamics - from stellar systems and galaxy disks, to the dynamics of the Local Group, large scale structures and motions, galaxy formation and general relativity. Each chapter is written by a world expert renowned for original contributions to the field. The authors are: James Binney, Roger Blandford, David Burstein, Tim de Zeeuw, George Efstathiou, Steve Gull, Nick Kaiser, J. Katz, Donald Lynden-Bell, Ruth Lynden-Bell, Douglas Lin, Jeremiah Ostriker, T. Padmanabhan, J. Papaloizou, Jim Peebles, Jim Pringle, Martin Rees, Maarteen Schmidt, Scott Tremaine and Simon White. This volume provides a broad, pedagogical introduction to gravitational dynamics for graduate students, and an up-to-date review for researchers in cosmology, astrophysics, mathematical physics and applied mathematics.
Download or read book Accreting White Dwarfs written by Edward M. Sion and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The astrophysical process of accretion onto compact central objects is ubiquitous across the universe. The study of white dwarf stars has greatly expanded in recent years, and this book presents, from first principles, the physics of the accretion process onto white dwarfs. Among the resulting phenomena are isolated white dwarfs accreting interstellar gas and dust as they orbit the galactic center, white dwarfs accreting from the debris disks of tidally disrupted asteroids, comets and exoplanets in other exoplanetary systems, white dwarfs accreting from red giant winds in symbiotic variable stars, white dwarfs accreting from Roche lobe-detached main sequence stars, white dwarfs accreting in cataclysmic variables, helium accreting white dwarfs in the ultra-compact AM CVn binaries, accreting white dwarf explosions in classical novae and Type Ia supernovae, the cosmologically critical white dwarf supernovae that led to the discovery of the accelerating expansion of the universe and the existence of dark energy. This book is intended for advanced undergraduates, graduate students, astrophysicists who specialize in white dwarf studies as well as non-specialist scientists.
Download or read book White Dwarfs and the Ages of Open Clusters written by Elizabeth Jane Jeffery and published by . This book was released on 2009 with total page 504 pages. Available in PDF, EPUB and Kindle. Book excerpt: Open clusters have long been objects of interest in astronomy. As a good approximation of essentially pure stellar populations, they have proved very useful for studies in a wide range of astrophysically interesting questions, including stellar evolution and atmosphere, the chemical and dynamical evolution of our Galaxy, and the structure of our Galaxy. Of fundamental importance to our understanding of open clusters, as well as many other questions in astrophysics, is the accurate determination of ages. Currently there are two main techniques for independently determining the ages of stellar populations: main sequence evolution theory (via cluster isochrones) and white dwarf cooling theory. Open clusters provide the ideal environment for the calibration of these two important clocks, as well as the unique opportunity to directly compare and refine our understanding of both theories. Here I present a photometric study of six open clusters, including both ground-based data, and new, deep photometric data from the Hubble Space Telescope. From the former I derive main sequence turn off ages, while the latter will be used to search for faint cluster white dwarfs. From these data I measure a white dwarf age for each cluster and directly compare these ages with those I find from the main sequence turn off age. For this analysis I employ a new Bayesian statistical technique that has been developed by our group. Additionally, I use this new technique to explore the feasibility of a new method to determine cluster white dwarf ages from the hot (bright) white dwarfs alone, and its first successful application to the Hyades.
Download or read book From Pulsations to Planetary Debris written by Zachary Philip Vanderbosch and published by . This book was released on 2021 with total page 390 pages. Available in PDF, EPUB and Kindle. Book excerpt: The final fates of stars and their planetary systems are in most cases embodied by white dwarfs. These are the compact remnants of stellar evolution for all low- to intermediate-mass stars in our Galaxy, including the Sun. The relative simplicity of white dwarfs makes them valuable tools in a variety of astrophysical contexts, from placing limits on the age of our Galaxy, to measuring the bulk abundances of exoplanets via the presence of actively accreted metals in their atmospheres. White dwarfs can also exhibit photometric variability for a variety of reasons, both as isolated stars and in binary systems, providing insights into white dwarf structure and circumstellar environments. In this dissertation we first present novel techniques to identify variable white dwarfs in modern time-domain photometric surveys. We then focus on identifying and characterizing two types of variable white dwarfs: those that pulsate and those being transited by circumstellar planetary debris. Using the unprecedented number of white dwarfs observed by Gaia and the Zwicky Transient Facility (ZTF), we define a set of variability metrics based on these publicly available catalogues to efficiently identify variable white dwarfs across the Gaia color magnitude diagram. We then present a dedicated search for pulsating He-atmosphere white dwarfs (DBVs) using McDonald Observatory follow-up observations, in an attempt to better define the observed extent of the helium-atmosphere white dwarf instability strip. We increase the number of DBVs from 28 to 47 using Sloan Digital Sky Survey spectroscopy to initially identify candidate DBVs. We find the observed blue and red edges of the DB instability strip are still hotter than theoretical expectations by about 1500K and 600K, respectively. Using our set of Gaia and ZTF variability metrics, we identify and characterize the second and third cases of white dwarfs with recurring planetary debris transits, with debris orbital periods differing by more than two orders of magnitude. These objects, in combination with the first known system, probe a unique parameter space constraining earlier stages of the planetary debris disruption and migration process
Download or read book Fundamentals of Galaxy Dynamics Formation and Evolution written by Ignacio Ferreras and published by UCL Press. This book was released on 2019-04-02 with total page 200 pages. Available in PDF, EPUB and Kindle. Book excerpt: Galaxies, along with their underlying dark matter halos, constitute the building blocks of structure in the Universe. Of all fundamental forces, gravity is the dominant one that drives the evolution of structures from small density seeds at early times to the galaxies we see today. The interactions among myriads of stars, or dark matter particles, in a gravitating structure produce a system with fascinating connotations to thermodynamics, with some analogies and some fundamental differences. Ignacio Ferreras presents a concise introduction to extragalactic astrophysics, with emphasis on stellar dynamics, and the growth of density fluctuations in an expanding Universe. Additional chapters are devoted to smaller systems (stellar clusters) and larger ones (galaxy clusters). Fundamentals of Galaxy Dynamics, Formation and Evolution is written for advanced undergraduates and beginning postgraduate students, providing a useful tool to get up to speed in a starting research career. Some of the derivations for the most important results are presented in detail to enable students appreciate the beauty of maths as a tool to understand the workings of galaxies. Each chapter includes a set of problems to help the student advance with the material.
Download or read book Galaxy Formation and Evolution written by Houjun Mo and published by Cambridge University Press. This book was released on 2010-05-20 with total page 841 pages. Available in PDF, EPUB and Kindle. Book excerpt: A coherent introduction for researchers in astronomy, particle physics, and cosmology on the formation and evolution of galaxies.
Download or read book White Dwarfs Composition Mass Budget and Galactic Evolution written by Volker Weidemann and published by . This book was released on 1975 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book New Worlds New Horizons in Astronomy and Astrophysics written by National Research Council and published by National Academies Press. This book was released on 2011-02-04 with total page 324 pages. Available in PDF, EPUB and Kindle. Book excerpt: Driven by discoveries, and enabled by leaps in technology and imagination, our understanding of the universe has changed dramatically during the course of the last few decades. The fields of astronomy and astrophysics are making new connections to physics, chemistry, biology, and computer science. Based on a broad and comprehensive survey of scientific opportunities, infrastructure, and organization in a national and international context, New Worlds, New Horizons in Astronomy and Astrophysics outlines a plan for ground- and space- based astronomy and astrophysics for the decade of the 2010's. Realizing these scientific opportunities is contingent upon maintaining and strengthening the foundations of the research enterprise including technological development, theory, computation and data handling, laboratory experiments, and human resources. New Worlds, New Horizons in Astronomy and Astrophysics proposes enhancing innovative but moderate-cost programs in space and on the ground that will enable the community to respond rapidly and flexibly to new scientific discoveries. The book recommends beginning construction on survey telescopes in space and on the ground to investigate the nature of dark energy, as well as the next generation of large ground-based giant optical telescopes and a new class of space-based gravitational observatory to observe the merging of distant black holes and precisely test theories of gravity. New Worlds, New Horizons in Astronomy and Astrophysics recommends a balanced and executable program that will support research surrounding the most profound questions about the cosmos. The discoveries ahead will facilitate the search for habitable planets, shed light on dark energy and dark matter, and aid our understanding of the history of the universe and how the earliest stars and galaxies formed. The book is a useful resource for agencies supporting the field of astronomy and astrophysics, the Congressional committees with jurisdiction over those agencies, the scientific community, and the public.
Download or read book The Origin and Evolution of Galaxies written by J.T. Jones and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 359 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Origin and Evolution of Galaxies is the outstanding problem of modern cosmology. Fortunately. we have a firm cosmological framework on which to base our theories (the hot big bang) and recently there has been substantial progress in providing observations which potentially can constrain these theories. The problem of galaxy formation is. as a consequence. one involving many diverse branches of physics and astrophysics. It has been the aim of the school. and this compendium of lectures and seminars. to bring together these diverse aspects at a level enabling research workers to understand what is going on in other corners of the subject and to see how progress in each area impinges on the others. We are grateful to the contributors to this volume for allowing us considerable editorial license with their articles. We have attempted to provide a representative sample of the talks that were given at the school besides the texts of the invited lecturers. It is regrettable that for reasons of space we have had to leave out a number of other contributions.
Download or read book Exoplanet Science Strategy written by National Academies of Sciences, Engineering, and Medicine and published by National Academies Press. This book was released on 2019-01-17 with total page 187 pages. Available in PDF, EPUB and Kindle. Book excerpt: The past decade has delivered remarkable discoveries in the study of exoplanets. Hand-in-hand with these advances, a theoretical understanding of the myriad of processes that dictate the formation and evolution of planets has matured, spurred on by the avalanche of unexpected discoveries. Appreciation of the factors that make a planet hospitable to life has grown in sophistication, as has understanding of the context for biosignatures, the remotely detectable aspects of a planet's atmosphere or surface that reveal the presence of life. Exoplanet Science Strategy highlights strategic priorities for large, coordinated efforts that will support the scientific goals of the broad exoplanet science community. This report outlines a strategic plan that will answer lingering questions through a combination of large, ambitious community-supported efforts and support for diverse, creative, community-driven investigator research.
Download or read book Planets Stars and Stellar Systems written by Gerard Gilmore and published by Springer. This book was released on 2013-02-23 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This is volume 5 of Planets, Stars and Stellar Systems, a six-volume compendium of modern astronomical research, covering subjects of key interest to the main fields of contemporary astronomy. This volume on “Galactic Structure and Stellar Populations”, edited by Gerard F. Gilmore, presents accessible review chapters on Stellar Populations, Chemical Abundances as Population Tracers, Metal-Poor Stars and the Chemical Enrichment of the Universe, The Stellar and Sub-Stellar Initial Mass Function of Simple and Composite Populations, The Galactic Nucleus, The Galactic Bulge, Open Clusters and Their Role in the Galaxy, Star Counts and the Nature of Galactic Thick Disk, The Infrared Galaxy, Interstellar PAHs and Dust, Galactic Neutral Hydrogen, High-Velocity Clouds, Magnetic Fields in Galaxies, Astrophysics of Galactic Charged Cosmic Rays, Gamma-Ray Emission of Supernova Remnants and the Origin of Galactic Cosmic Rays, Galactic Distance Scales, Globular Cluster Dynamical Evolution, Dynamics of Disks and Warps, Mass Distribution and Rotation Curve in the Galaxy, Dark Matter in the Galactic Dwarf Spheroidal Satellites, and History of Dark Matter in Galaxies. All chapters of the handbook were written by practicing professionals. They include sufficient background material and references to the current literature to allow readers to learn enough about a specialty within astronomy, astrophysics and cosmology to get started on their own practical research projects. In the spirit of the series Stars and Stellar Systems published by Chicago University Press in the 1960s and 1970s, each chapter of Planets, Stars and Stellar Systems can stand on its own as a fundamental review of its respective sub-discipline, and each volume can be used as a textbook or recommended reference work for advanced undergraduate or postgraduate courses. Advanced students and professional astronomers in their roles as both lecturers and researchers will welcome Planets, Stars and Stellar Systems as a comprehensive and pedagogical reference work on astronomy, astrophysics and cosmology.
Download or read book Tidal Streams in the Local Group and Beyond written by Heidi Jo Newberg and published by Springer. This book was released on 2015-12-29 with total page 256 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume is written by leading scientists in the field, who review the current state of our knowledge of tidal streams in the Milky Way, the Andromeda galaxy, and in other nearby galaxies. The cosmological origins of dwarf galaxies and the physical processes by which they are tidally disrupted into streams and incorporated into galaxy halos are discussed. The techniques that have been used to identify tidal streams are presented and will be useful to researchers who would like to find substructures in the next generation of optical sky surveys, including Pan-STARRS and LSST. The methods that are currently under development to constrain both large scale distribution of dark matter in the Milky Way and the (small scale) lumpiness of the dark matter distribution are also explained. The authors also provide motivation for future spectroscopic surveys of Milky Way halo stars, which will aid both in the identification of tidal streams and the constraint of dark matter properties. This volume is aimed at graduate students who are beginning this field of research, but is also a resource for researchers who study tidal streams and related fields. In addition to presenting the physical processes by which tidal streams are created, it also reviews the current state of the observations and the progress towards utilizing these observations to constrain the distribution of dark matter in the Milky Way. The book will introduce anyone with a background in astrophysics to the field of tidal streams.
Download or read book The Impact of Binary Stars on Stellar Evolution written by Giacomo Beccari and published by Cambridge University Press. This book was released on 2019-04-18 with total page 359 pages. Available in PDF, EPUB and Kindle. Book excerpt: An advanced review of how binary stars affect stellar evolution, presenting results from state-of-the art models and recent observations.
