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Showing papers by "Edward L. Wright published in 1988"


Journal ArticleDOI
01 Nov 1988-Nature
TL;DR: In this article, the ultraviolet extinction curves of small spherical particles with the tensor dielectric constant of graphite but with the c-axis always running parallel to the radius vector were calculated using the discrete dipole approximation.
Abstract: Carbon particles in interstellar dust cause absorption of starlight at certain wavelengths. Kroto and McKay1 have suggested that such particles have the form of quasi-icosahedral spiral shells, with the hexagonal graphitic planes perpendicular to the radius, like the layers of an onion. Using the discrete dipole approximation (DDA)2 I have calculated the ultraviolet extinction curves of small spherical particles with the tensor dielectric constant of graphite but with the c-axis always running parallel to the radius vector. The feature at a wavelength of 2,200 A is doubled in width and moved to a wavelength about 80 A shorter in comparison to the parameters derived from the usual Mie theory approximation for a mixture of particles with scalar dielectric constants. For larger particles, the peak shifts to longer wavelengths, but for a radius of ∼300 A which puts the peak at 2,200 A (the same position as the mean interstellar absorption peak3), the width of absorption by quasi-icosahedral particles is too large to fit the data.

27 citations


Journal ArticleDOI
TL;DR: In this paper, the authors explored the possibility that the whole microwave background can be produced by a bright population of pregalactic stars at a redshift of a few hundred, and the possibility of producing deviations small enough to be consistent with the best available observations, but still detectable by COBE, was considered.
Abstract: The possibility that the whole microwave background can be produced by a bright population of pregalactic stars at a redshift of a few hundred is explored. The radiation is thermalized by a combination of amorphous silicate, amorphous carbon, graphite, and needle-shaped conducting grains which give rise to the opacity needed at wavelengths greater than 3 cm. The occurrence of distortion in a primordial microwave background spectrum due to its interaction with Population III stars and dust is investigated. The possibility of producing deviations small enough to be consistent with the best available observations, but still detectable by COBE, is considered.

24 citations


Journal Article
TL;DR: A Monte Carlo technique has been developed to compute the joint probability distribution for the reddening and extinction of quasars by galaxies along the line of sight with a realistic dust extinction curve including the 220 nm feature.
Abstract: A Monte Carlo technique has been developed to compute the joint probability distribution for the reddening and extinction of quasars by galaxies along the line of sight with a realistic dust extinction curve including the 220 nm feature. Galaxies are treated as disks with random inclinations, having exponential or modified Gaussian radial profiles. This technique is used to find the distribution of the reddened quasars on multicolor diagrams such as the (U-J, J-F) plots used by Koo and Kron (1982) to find faint quasars. The multicolor search technique is not a simple UV excess approach, and the resulting color selection does not add significantly to the flux selection discussed by Wright (1981), Ostriker and Heisler (1984), and Heisler and Ostriker (1988). The quasar reddening trend observed by Wright and Malkan (1987) is about 0.35 + or - 0.50 times the mean reddening of the selected sample predicted by the Heisler and Ostriker model.

17 citations


Journal ArticleDOI
TL;DR: In this paper, the observed properties of galaxies and galaxy-ensembles in the 'local' universe are extrapolated to high redshifts using reasonable scenarios for the evolution of galaxy and their spatial distribution.
Abstract: Techniques for simulating images of galaxy fields are presented that extend to high redshifts and a surface density of galaxies high enough to produce overlapping images. The observed properties of galaxies and galaxy-ensembles in the 'local' universe are extrapolated to high redshifts using reasonable scenarios for the evolution of galaxies and their spatial distribution. This theoretical framework is then employed with Monte Carlo techniques to create fairly realistic two-dimensional distributions of galaxies plus optical and near-infrared sky images in a variety of model universes, using the appropriate density, luminosity, and angular size versus redshift relations.

5 citations