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Arnett, W. D.

Publications and source records attributed to Arnett, W. D..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Carbon combustion supernovae - Numerical studies of the final evolution of degenerate carbon-oxygen cores

The evolution of polytropic 1.46-solar-mass 3-Gg/cu cm (4 x 10 to the 8th)-K pure C cores is investigated theoretically by means of model computations starting from the runaway stage. The temperature in central zones is raised to the runaway temperature, and the evolution is followed in a spherical coordinate system. In models of burning without detonation, it is found that the initially spherical burning front is Rayleigh-Taylor unstable, without bipolar jets or equatorial rings; that some C is not burned to Ni; and that the Ni in the 0.8-1.0 solar mass of burned fuel produced can account for observed properties of type I supernovae.

Mueller, E.↗
NASA NTRS1982

The cosmic distance scale - Methods for determining the distance to supernovae

It is established by an analysis of alternative methods for the determination of absolute distances to supernovae that there exists a kinematic method, superior to that of Baade (1926), which is illustrated for the case of the Type I supernova 1975a in NGC 2207. In addition, a dynamical method is developed which employs the recently-discovered analytic solutions for Type I supernovae. The requirement that the paradigm invoked in the present study be able to reproduce both fast and slow light curves has implied a dispersion in intrinsic brightness, whose size is approximately that observed in the Virgo and Coma clusters.

Arnett, W. D.↗
NASA NTRS1981

Pulsar statistics and their interpretations

It is shown that a lack of knowledge concerning interstellar electron density, the true spatial distribution of pulsars, the radio luminosity source distribution of pulsars, the real ages and real aging rates of pulsars, the beaming factor (and other unknown factors causing the known sample of about 350 pulsars to be incomplete to an unknown degree) is sufficient to cause a minimum uncertainty of a factor of 20 in any attempt to determine pulsar birth or death rates in the Galaxy. It is suggested that this uncertainty must impact on suggestions that the pulsar rates can be used to constrain possible scenarios for neutron star formation and stellar evolution in general.

Arnett, W. D.↗
NASA NTRS1981

Hydrodynamic effects of a stellar explosion on a binary companion star

The impact of an expanding supernova shell on a companion star is investigated. The results of a two-dimensional numerical hydrodynamic calculation are compared to the results of previous attempts to solve the problem analytically which assumed the stellar surface to be planar. The curved surface of the star and the finite thickness of the shell are found to have a significant effect in reducing the drag on the companion. In addition, not all of the matter which is ablated from the star is ejected straight back toward the supernova, further reducing the momentum imparted to the companion. As a result, the final momentum of the companion star is actually less than the incident momentum of the shell. It seems unlikely that the collision between the supernova shell and the companion star will have a significant effect on the orbit of the binary, except perhaps in extreme cases.

Fryxell, B. A.↗
NASA NTRS1978

Gamma line radiation from supernovae

Recent calculations of core collapse or massive stars result in explosive ejection of the mantle by a reflected shock. These hydrodynamic results are important for predictions of explosive nucleosynthesis and gamma-ray line emission from supernovae. Previous estimates, based on simple parameterized models or the nucleosynthesis in an average supernova, are compared with these latest results.

Arnett, W. D.↗
NASA NTRS1977

Gamma rays and supernova explosions

Thermal radiation associated with the explosion of supernovae is investigated. High temperature is required to produce copious gamma radiation of this sort. It appears that type 11 supernovae do not release much of their energy as gamma ray continuum radiation.

Arnett, W. D.↗
NASA NTRS1976

Gamma rays and supernova explosions

The detection of gamma rays from supernovae will provide interesting tests of current theory. Some current ideas on the expected gamma ray flux, as modified by recent theoretical results are reviewed.

Arnett, W. D.↗
NASA NTRS1974

On the e-process - Its components and their neutron excesses

The pattern of abundances within the iron-abundance peak of the solar system is analyzed for various Cr, Fe, and Ni abundances, and a method is developed for finding the best fit to a given set of abundances with a chosen number of zones, i.e., mass contributions characterized by differing values of eta. This material can be synthesized by a superposition of e-process compositions in a low-eta region (eta = 0.003) and a high-eta region (eta = 0.065 -0.080) with at least 85% coming from the low-eta region. Addition of a third eta zone is unproductive. The applicability of the particle-poor freeze out is discussed in the light of these abundances, and the results of employing different numbers and types of zones are interpreted as an indication of the relative abundances themselves. Ejection of the low-eta zones is of great interest in gamma-ray astronomy and for empirical testing of theories of nucleosynthesis. The distribution of high zones should give important information about the formation of collapsed remnants.

Hainebach, K. L.↗
NASA NTRS1973

The evolution of galaxies. III - Metal-enhanced star formation

The problem of the paucity of low-metal-abundance low-mass stars is discussed. One alternative to the variable-initial-mass-function (VIMF) solution is proposed. It is shown that this solution - metal-enhanced star formation - satisfies the classical test which prompted the VIMF hypothesis. Furthermore, with no additional parameters it provides improved fits to other tests - e.g., inhomogeneities in the abundances in young stars, concordance of all nucleo-cosmochronologies, and a required yield of heavy-element production which is consistent with current stellar evolution theory. In this model the age of the Galaxy is 18.6 plus or minus 5.7 b.y.

Talbot, R. J., Jr.↗
NASA NTRS1968

On Supernova Hydrodynamics

Rebuttal to Colgate criticism of Arnett investigation of gravitational collapse of nonrotating massive stars, discussing energy transport, equation of state and neutrino effects

Arnett, W. D.↗
NASA NTRS1967

Supernova hydrodynamics and nucleosynthesis.

Core of two solar masses of gravitationally collapsing star, analyzing hydrodynamics, heating, helium 4 formation, neutron decay, nucleosynthesis, light output and mass ejection

SUPERNOVA↗