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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
TL;DR: In this paper, the mass distribution of DA white dwarfs from the Palomar Green (PG) survey was derived and the luminosity function of the sample, weighted by 1/Vmax, was obtained and compared with other determinations.
Abstract: Spectrophotometric observations at high signal-to-noise ratio were obtained of a complete sample of 348 DA white dwarfs from the Palomar Green (PG) Survey. Fits of observed Balmer lines to synthetic spectra calculated from pure-hydrogen model atmospheres were used to obtain robust values of Teff, log g, masses, radii, and cooling ages. The luminosity function of the sample, weighted by 1/Vmax, was obtained and compared with other determinations. Incompleteness of the sample due to selection by photographic mu - mb color and magnitude limits was found to be a serious problem, and an attempt is made to correct for this. The mass distribution of the white dwarfs is derived, after important corrections for the radii of the white dwarfs in this magnitude-limited survey and for the cooling time scales. This distribution has (1) a "peak" component centered near 0.6 M⊙, (2) a low-mass component centered near 0.4 M⊙, and (3) a high-mass component above about 0.8 M⊙. The formation rate of DA white dwarfs from the PG is estimated to be 0.6 × 10-12 pc-3 yr-1. Of these, 75% are from the peak component, 10% from the low-mass component, and 15% from the high-mass component. The low-mass component requires binary evolution for 100% of the objects, with a degenerate companion likely in the majority of cases. Comparison with predictions from a theoretical study of the white dwarf formation rate for single stars indicates that ≥80% of the high-mass component requires a different origin, presumably mergers of lower mass double degenerate stars. The need for a binary channel may not be as great for the massive, very hot white dwarfs found in the EUV all-sky surveys. In an Appendix, we even suggest that an enhanced density of the massive white dwarfs at lower Galactic latitudes might be due to some of them being the progeny of B stars in Gould's Belt. In order to estimate the recent formation rate of all white dwarfs in the local Galactic disk, corrections for incompleteness of the PG, addition of the DB-DO white dwarfs, and allowance for stars hidden by luminous binary companions had to be applied to enhance the rate. An overall formation rate of white dwarfs recently in the local Galactic disk of (1 ± 0.25) × 10-12 pc-3 yr-1 is obtained. Admittedly, the systematic errors in this estimate are difficult to quantify. Two recent studies of samples of nearby Galactic planetary nebulae lead to estimates around twice as high. Difficulties in reconciling these determinations are discussed.

490 citations

Journal ArticleDOI
TL;DR: In this article, the authors systematically examine how the presence in a binary affects the final core structure of a massive star and its consequences for the subsequent supernova explosion, and suggest that the core collapse in an electron-capture supernova (and possibly in the case of relatively small iron cores) leads to a prompt or fast explosion rather than a very slow, delayed neutrino-driven explosion.
Abstract: We systematically examine how the presence in a binary affects the final core structure of a massive star and its consequences for the subsequent supernova explosion Interactions with a companion star may change the final rate of rotation, the size of the helium core, the strength of carbon burning, and the final iron core mass Stars with initial masses larger than � 11 Mthat experience core collapse will generally have smaller iron cores at the point of explosion if they lost their envelopes through a binary interaction during or soon after core hydrogen burning Stars below � 11 M� , on the other hand, can end up with larger helium and metal cores if they have a close companion, since the second dredge-up phase that reduces the helium core mass dramatically in single stars does not occur once the hydrogen envelope is lost We find that the initially more massive stars in binary systems with masses in the range 8-11 Mare likely to undergo an electron-capture supernova, while single stars in the same mass range would end as ONeMg white dwarfs We suggest that the core collapse in an electron-capture supernova (and possibly in the case of relatively small iron cores) leads to a prompt or fast explosion rather than a very slow, delayed neutrino-driven explosion and that this naturally produces neutron stars with low-velocity kicks This leads to a dichotomous distribution of neutron star kicks, as inferred previously, where neutron stars in relatively close binaries attain low kick velocities We illustrate the consequences of such a dichotomous kick scenario using binary population synthesis simulations and discuss its implications This scenario has also important consequences for the minimum initial mass of a massive star that becomes a neutron star For single stars the critical mass may be as high as 10-12 M� , while for close binaries it may be as low as 6-8 M� T hese critical masses depend on the treatment of convection, the amount of convective overshooting, and the metal- licity of the star, and will generally be lower for larger amounts of convective overshooting and lower metallicity Subject heading

487 citations

Journal ArticleDOI
TL;DR: In this paper, a grid of hydrogen-and helium-rich white dwarf model atmospheres is used to calculate absolute visual magnitudes, masses, and ages for each model from detailed evolutionary cooling sequences appropriate for these stars.
Abstract: Bolometric corrections and color indices on various photometric systems are provided for an extensive grid of hydrogen- and helium-rich white dwarf model atmospheres. Absolute visual magnitudes, masses, and ages are also obtained for each model from detailed evolutionary cooling sequences appropriate for these stars. The results of our calculations are briefly compared with published observational material. These calculations can easily be extended to any given photometric system.

482 citations

Journal ArticleDOI
TL;DR: Theoretical light curves and photospheric expansion velocities are compared with observations of 27 Type Ia supernovae (SNe Ia) in this article, and the results are discussed in detail and applied to determine Ho and qo.
Abstract: Theoretical monochromatic light curves and photospheric expansion velocities are compared with observations of 27 Type Ia supernovae (SNe Ia). A set of 37 models has been considered which encompasses all currently discussed explosion scenarios for Type Ia supernovae including deflagrations, detonations, delayed detonations, pulsating delayed detonations and tamped detonations of Chandra- mass, and Helium detonations of low mass white dwarfs. The explosions are calculated using one-dimensional Lagrangian hydro and radiation-hydro codes with incorporated nuclear networks. Subsequently, light curves are constructed using our LC scheme which includes an implicit radiation transport, expansion opacities, a Monte-Carlo $\gamma $-ray transport, and molecular and dust formation. For some supernovae, results of detailed non-LTE calculations have been considered. Observational properties of our series of models are discussed, the relation between the absolute brightness, post-maximum decline rates, the colors at several moments of time, etc. All models with a Ni production larger than 0.4 solar masses produce light curves of similar brightness. The influence of the cosmological red shift on the light curves and on the correction for interstellar reddening is discussed. Based on data rectification of the standard deviation, a quantitative procedure to fit the observations has been used to the determine the free parameters, i.e. the correct model, the distance, the reddening, and the time of the explosion. The results are discussed in detail and applied to determine Ho and qo.

480 citations

Journal ArticleDOI
TL;DR: In this article, a suite of fourteen three-dimensional, high-resolution hydrodynamical simulations of delayed-detonation models of Type Ia supernova (SN Ia) explosions is presented.
Abstract: We present results for a suite of fourteen three-dimensional, high resolution hydrodynamical simulations of delayed-detonation models of Type Ia supernova (SN Ia) explosions. This model suite comprises the first set of three-dimensional SN I a simulations with detailed isotopic yield information. As such, it may serve as a database for Chandrasekhar-mass delayeddetonation model nucleosynthetic yields and for deriving synthetic observables such as spectra and light curves. We employ a physically motivated, stochastic model based on turbulent velocity fluctuations and fuel density to calculate in situ t he deflagration to detonation transition (DDT) probabilities. To obtain different strengths of the deflagration phase and thereby different degrees of pre-expansion, we have chosen a sequence of initial models with 1, 3, 5, 10, 20, 40, 100, 150, 200, 300, and 1600 (two different realizations) ignition kernels in a hydrostatic white dwarf with central density of 2.9× 10 9 g cm −3 , plus in addition one high central density (5.5× 10 9 g cm −3 ) and one low central density (1.0× 10 9 g cm −3 ) rendition of the 100 ignition kernel configuration. For each simulatio n we determined detailed nucleosynthetic yields by post-processing 10 6 tracer particles with a 384 nuclide reaction network. All delayed detonation models result in explosions unbinding the white dwarf, producing a range of 56 Ni masses from 0.32 to 1.11 M⊙. As a general trend, the models predict that the stable neutron-rich iron group isotopes are not found at the lowest velocities, but rather at intermediate velocities (∼3, 000− 10, 000 km s −1 ) in a shell surrounding a 56 Ni-rich core. The models further predict relatively low velocity oxygen and carbon, with typical minimum velocities around 4, 000 and 10, 000 km s −1 , respectively.

477 citations


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