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White dwarf

About: White dwarf is a research topic. Over the lifetime, 15004 publications have been published within this topic receiving 430597 citations. The topic is also known as: degenerate dwarf.


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Journal ArticleDOI
01 Jun 1992-Nature
TL;DR: In this article, a new model for γ-ray bursts at cosmological distances was proposed, based on the formation of rapidly rotating neutron stars with surface magnetic fields of the order of 1015.
Abstract: THE spatial and luminosity distribution of γ-ray bursts as observed by the BATSE instrument on the Compton Gamma Ray Observatory1,2 provides support for the revival of the idea3,4 that the burst sources are at cosmological distances5. I present here a new model for γ-ray bursts at cosmological distances, based on the formation of rapidly rotating neutron stars with surface magnetic fields of the order of 1015. Such objects could form by the gravitational collapse of accreting white dwarfs with anomalously high magnetic fields in binaries, as in magnetic cataclysmic binaries. Once formed, such rapidly rotating and strongly magnetized neutron stars would lose their rotational kinetic energy catastrophically, on a timescale of seconds or less: rotation of the magnetic field creates a strong electric field, and hence an electron–positron plasma, which I show to be optically thick and in quasi-thermodynamic equilibrium. This plasma flows away from the neutron star at relativistic speeds, and X-ray and γ-ray emission at the photosphere of this relativistic wind may then reproduce the observational characteristics of a γ-ray burst.

1,011 citations

Journal ArticleDOI
TL;DR: In this article, it is argued that most of the magnetic energy becomes concentrated in thin flux ropes when the field pressure exceeds the turbulent pressure at the smallest scale of turbulence, and the possibilities for dynamo action during the various (precollapse) stages of convective motion that occur in the evolution of a massive star are examined.
Abstract: Neutron star convection is a transient phenomenon and has an extremely high magnetic Reynolds number In this sense, a neutron star dynamo is the quintessential fast dynamo The convective motions are only mildly turbulent on scales larger than the approximately 100 cm neutrino mean free path, but the turbulence is well developed on smaller scales Several fundamental issues in the theory of fast dynamos are raised in the study of a neutron star dynamo, in particular the possibility of dynamo action in mirror-symmetric turbulence It is argued that in any high magnetic Reynolds number dynamo, most of the magnetic energy becomes concentrated in thin flux ropes when the field pressure exceeds the turbulent pressure at the smallest scale of turbulence In addition, the possibilities for dynamo action during the various (pre-collapse) stages of convective motion that occur in the evolution of a massive star are examined, and the properties of white dwarf and neutron star progenitors are contrasted

917 citations

BookDOI
01 Jan 1983
TL;DR: Reference frame studies at JPL/Caltech as mentioned in this paper have been carried out in the past few decades to study the properties of stellar magnetic fields and their relationship with the Earth's magnetic field.
Abstract: Invited Discourses.- Pulsars and their Genesis.- Dark Matter in the Universe.- Venus.- Joint Discussions.- 1. Reference Frames.- Uses and Required Characteristics of Reference Frames for Galactic Astronomy.- Reference Frames for Minor Planets, Comets and Satellites.- Reference Frames and the Extragalactic Distance Scale.- Requirements for Earth Rotation Parameters.- Ephemerides and Celestial Mechanics.- Status Report on the Work on the FK5.- J2000.0.- Classical Absolute/Differential Programs.- The Background to the MERIT/COTES Recommendations on the Terrestrial and Celestial Reference Systems.- HIPPARCOS and Celestial Reference Frame.- The Use of the Hubble Space Telescope for Global Reference Frame Work.- Proper Motions Referred to Faint Galaxies.- Reference Frame Studies at JPL/ Caltech.- On the Use of Natural References.- Relativistic Reference Frames in Astrometry.- Comparison of the Optical and Radio Reference Frames.- The Promise of Optical/IR Interferometry and Space Astrometry.- Reference Frame/Coordinate System in General Relativity.- Discussions.- 2. Long-Period Eclipsing Binary Stars and Related Objects.- Photometry of the Recent Eclipse of Epsilon Aurigae.- A Spectroscopic View of Epsilon Aurigae.- Interpretation of the Data of Epsilon Aurigae.- Observation and Interpretation of Zeta Aurigae Stars.- Related Binaries, Including Symbiotic Stars.- Mass Transfer and Evolution in Long-Period Binary Systems.- Wind Accretion and Interaction in Long Period Binary Systems.- Summary and Critique of Joint Discussion II.- Extraction of the Shell Spectrum of Epsilon Aurigae.- Dynamics of the Epsilon Aurigae Ring Model.- Interim Discussion of the Orbit of ? Sagittae.- Evidence for the Roche Lobe Overflow in VV Cephei.- Infrared Michelson Interferometry of Zeta Aurigae Type Supergiants.- Very Long Period Supergiant Semidetached and Contact Systems.- 3. Solar and Stellar Nonradial Oscillations.- Progress and Problems in the Study of the Pulsating White Dwarf Stars.- The PG1159 Variables.- Non-Radial Oscillations in ? Scuti Stars and Rapidly Oscillating Ap Stars.- Beta Cephei Variables.- Nonradial and Radial Oscillations Observed in Non-Emission Line OB Dwarfs and Giants.- Non-Radial Pulsation in Be Stars.- Radial and Non-Radial Pulsations in Wolf-Rayet Stars and in Supergiants.- Solar and Solar-Like Oscillations: Theory.- 4. Radio Astronomy and Cosmology.- Cosmic Microwave Background Spectrum Measurements.- The Angular Distribution of the Cosmic Background Radiation.- Ovro Results on the Sunyaev-Zel'dovich Effect, 1983-1985.- The Microwave Background from Cambridge.- Searches for Primordial Pancakes.- Intergalactic Neutral Hydrogen.- The Nature of Faint Radio Sources.- Is the Upturn in the Source Counts Caused by Primeval Radio Galaxies ?.- A New Deep VLA Radio Survey at 6 cm.- Dependence of Linear Sizes and Spectral Indices of Extended Radio Galaxies on Redshift and Radio Luminosity.- Abundances of the Very Light Elements (D, 3He, 4He and 7Li) and Primordial Nucleosynthesis.- 5. Stellar Activity: Rotation and Magnetic Fields.- Stellar Dynamo Characteristics.- Stellar Activity Cycles.- On the Rotation-Activity Connection.- Convection as a Regulator of Dynamos.- The Measurement of Stellar Photospheric Magnetic Fields.- The Dichotomy Between CO Absorptions and Ca II Emissions in the Sun and Stars: An Indirect Diagnostic for Gas Disturbed by Magnetic Fields ?.- Starspots and Plages.- A Study of Three RS CVn-type Eclipsing Binaries.- Coronal Magnetic Fields.- Properties of Stellar Magnetic Fields in Close Binaries Deduced from Non-thermal Radio Observations.- Stellar X-ray and Radio Activities and Coronal Magnetic Field.- On Active Stars, Coronal Loops, Magnetic Braking and All That.- 6. Evolution in Young Populations in Galaxies.- The Concept of Young Populations.- Evolution of High Mass Stars.- The Dynamical Evolution of Young Clussters and Associations.- The Initial Mass Function in Young Star Clusters.- Discussion.- Structure and Evolution of Giant Molecular Clouds.- Molecular Clouds in M51 and in the Galaxy.- The Molecular Cloud Content of Spiral and Dwarf Galaxies.- Discussion.- Star Formation, Giant HII Regions and Spiral Structure.- Young Stars and Star Formation in Normal Irregular Galaxies.- Discussion.- Chemical Evolution of Galaxies.- Star Formation Bursts in Galaxies.- Discussion.- Summary.- 7. Supernovae.- Centenary of S Andromedae (SN 1885a).- Problems of Observing Nearby Galaxies Visually.- Some Possible Identification Between Chinese Guest Stars and Supernova Remnants.- Supernovae in Flocculent and Grand Design Galaxies.- Recent Optical Observations of Supernovae.- Supernovae and Stellar Mass Loss.- Models for the Early and Late Spectra of Supernovae.- NL TE-Effects in Supernovae Type II Photospheres.- Models of Type II Supernova Explosions.- Effects of Angular Momentum on Supernova Explosion and Stability of Rapidly Rotating Stellar Cores.- Gravitational Radiation by a Collapsing Rotating Stellar Core.- Phase Transitions of Superdense Matter and Supernova Explosion.- X-ray Emission from Supernova Remnants.- Supernovae and Cosmology.- VL BI Observations of the Compact Components in M82.- Radio Supernova Candidates in the M82 Starburst.- Joint Commission Meetings.- Hipparcos.- The ESA Space Astrometry Mission: Overview and Status.- Activities of the Input Catalogue Consortium.- Preparation of the Mission: Earth-based Photometry.- Preparation of the Mission: Earth-based Astrometry.- Activities of the Data Reduction Consortia.- Tycho: Photometry & Astrometry for more than 500 000 Stars.- The Tycho Input Catalogue.- Link with Extragalactic Reference Frames.- Coronal Activity and Interplanetary Disturbances.- Coronal Activity at Radio Wavelengths.- Coronal Response to Energy Release During Solar Flares.- Correlated Observations of Impulsive UV and Hard X-ray Bursts from the Solar Maximum Mission.- Coronal Mass Ejections.- The Sources of Major Heliospheric Disturbances.- The Response of Microwave Emission to the Development of Active Regions.- Coronal Holes and Flare Related Phenomena.- Coronal Structures Observed at Meter Wavelengths.- The Nancay Multifrequency Radioheliograph.- An Energy Storage Mechanism for a Solar Flare by Shearing the Magnetic Field.- Merit + Cotes.- Joint Summary Report of the IAU/IUGG Working Groups on the Rotation of the Earth and the Terrestrial Reference System.- Report of Joint Meeting Held on 1985 November 22 to consider the MERIT/COTES Recommendations for a New International Earth-rotation Service.- Synthetic Photometry.- Principles and Scope of Synthetic Photometry.- The Possibilities of Synthetic Photometry.- Passbands and Photometric Systems.- Observed Stellar Energy Distributions for Synthetic Photometry.- Theoretical Stellar Energy Distributions.- Synthetic Photometry and the Calibration of the Hubble Space Telescope.- Standard Stars.- The Microfiche of Standard Stars.- Energy Distribution, Photometry and Physical Characteristics of the Sun and Solar Analogs.- On the Absolute Energy Distributions of the Sun, of the "Solar Analogs" 16 Cyg B, 16 Cyg A, VB 64 and of Vega.- Note.- Additional Contributions.- New Radio Telescopes.- A Reconsideration of the Galactic Constants.- Author Index.

912 citations

Journal ArticleDOI
TL;DR: In this article, the authors review the significant recent observational progress in addressing the progenitor problem and consider clues that have emerged from the observed properties of the various proposed proggenitor populations, from studies of SN Ia sites.
Abstract: Type Ia supernovae (SNe Ia) are important distance indicators, element factories, cosmic-ray accelerators, kinetic-energy sources in galaxy evolution, and end points of stellar binary evolution. It has long been clear that a SN Ia must be the runaway thermonuclear explosion of a degenerate carbon-oxygen stellar core, most likely a white dwarf (WD). However, the specific progenitor systems of SNe Ia, and the processes that lead to their ignition, have not been identified. Two broad classes of progenitor binary systems have long been considered: single-degenerate (SD), in which a WD gains mass from a nondegenerate star; and double-degenerate (DD), involving the merger of two WDs. New theoretical work has enriched these possibilities with some interesting updates and variants. We review the significant recent observational progress in addressing the progenitor problem. We consider clues that have emerged from the observed properties of the various proposed progenitor populations, from studies of SN Ia sites—...

860 citations

Journal ArticleDOI
TL;DR: In this article, photospheric abundances for 27 elements from carbon to europium in 181 F and G dwarfs from a differential local thermodynamic equilibrium (LTE) analysis of high-resolution and high signal-to-noise ratio spectra were presented.
Abstract: Photospheric abundances are presented for 27 elements from carbon to europium in 181 F and G dwarfs from a differential local thermodynamic equilibrium (LTE) analysis of high-resolution and high signal-to-noise ratio spectra. Stellar effective temperatures (T eff) were adopted from an infrared flux method calibration of Stromgren photometry. Stellar surface gravities (g) were calculated from Hipparcos parallaxes and stellar evolutionary tracks. Adopted T eff and g values are in good agreement with spectroscopic estimates. Stellar ages were determined from evolutionary tracks. Stellar space motions (U , V , W ) and a Galactic potential were used to estimate Galactic orbital parameters. These show that the vast majority of the stars belong to the Galactic thin disc. Relative abundances expressed as (X/Fe) generally confirm previously published results. We give results for C, N, O, Na, Mg, Al, Si, S, K, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Sr, Y, Zr, Ba, Ce, Nd and Eu. The α elements - O, Mg, Si, Ca and Ti - show (α/Fe) to increase slightly with decreasing (Fe/H). Heavy elements with dominant contributions at solar metallicity from the s-process show (s/Fe) to decrease slightly with decreasing (Fe/H). Scatter in (X/Fe) at a fixed (Fe/H) is entirely attributable to the small measurement errors, after excluding the few thick disc stars and the s-process-enriched CH subgiants. Tight limits are set on 'cosmic' scatter. If a weak trend with (Fe/H) is taken into account, the composition of a thin disc star expressed as (X/Fe) is independent of the star's age and birthplace for elements contributed in different proportions by massive stars (Type II supernovae), exploding white dwarfs (Type Ia supernovae) and asymptotic red giant branch stars. By combining our sample with various published studies, comparisons between thin and thick disc stars are made. In this composite sample, thick disc stars are primarily identified by their V LSR in the range −40 to −100 km s −1 . These are very old stars with origins in the inner Galaxy and metallicities (Fe/H) −0.4. At the same (Fe/H), the sampled thin disc stars have V LSR ∼ 0k m s −1 , and are generally younger with a birthplace at about the Sun's Galactocentric distance. In the range −0.35 (Fe/H) −0.70, well represented by present thin and thick disc samples, (X/Fe) of the thick disc stars is greater than that of thin disc stars for Mg, Al, Si, Ca, Ti and Eu. (X/Fe) is very similar for the thin and thick disc for - notably - Na and iron-group elements. Barium ((Ba/Fe)) may be underabundant in thick relative to thin disc stars. These results extend previous ideas about composition differences between the thin and thick disc.

832 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023367
2022667
2021495
2020557
2019548
2018515