Showing papers by "Mike Irwin published in 1988"
TL;DR: In this paper, a new optical technique for surveying large numbers of quasars for evidence of gravitational lensing is described, which is effective for separations greater than about two arcseconds, and allows the probability of detecting a lens of specified magnitude, component magnitude difference and component separation to be precisely calculated.
Abstract: A new optical technique for surveying large numbers of quasars for evidence of gravitational lensing is described. Using the Automated Plate Measuring Facility at Cambridge to scan broadband direct and objective-prism plates, hundreds of thousands of objects can be examined to find quasar candidates with multiple image structures. The technique is effective for separations greater than about two arcseconds, and allows the probability of detecting a lens of specified magnitude, component magnitude difference, and component separation to be precisely calculated. Tables are given that quantify the probability of detection of multiply imaged quasars. When combined with the large numbers of quasars surveyed, specific theoretical predictions of the frequency of lensing can be directly tested. The results of a survey of 2500 quasars with magnitudes in the range of 17-20 covering 130 sq deg of sky are described. Significant new limits can be put on the numbers of gravitationally lensed quasars with wide image separations. These limits enable some calculations of the distribution of mass in the universe to be undertaken. In particular, limits can be placed on the numbers of cosmic strings in the universe. 21 references.
15 citations
TL;DR: In this paper, the authors describe the detection of 69 galaxies with a raie d'emission Hα dans les amas de galaxies A 347 and A 1367.
Abstract: Detection de 69 galaxies a raie d'emission Hα dans les amas de galaxies A 347 et A 1367 a l'aide d'un prisme a objectif de haute dispersion. Le resultat des mesures est compare a celui obtenu par d'autres moyens d'investigation. Les flux et largeur equivalente du profil Hα+[N II] sont estimes et les redshifts grossierement determines
15 citations
Journal Article•
4 citations
01 Jan 1988
TL;DR: For decades, star counts and HR diagrams extending below the main sequence turnoff in globular clusters meant the work of Sandage (1957) and made clear that clusters differ in the shapes of their luminosity functions and in the morphology of their HR diagrams as mentioned in this paper.
Abstract: For decades, star counts and HR diagrams extending below the main sequence turnoff in globular clusters meant the work of Sandage (1957). The advent of large CCD’s at the foci of large telescopes has changed this (McClure et al. 1985, Harris & Hesser 1985, Christian & Heasley 1986, Heasley et al. 1986, Penny & Dickens 1986, Richer & Fahlman 1986, Smith et al. 1986) and made clear that clusters differ in the shapes of their luminosity functions and in the morphology of their HR diagrams. We return here to photographic methods, which can capture an order of magnitude more images and so possibly reveal new details.
1 citations