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Melville P. Ulmer

Bio: Melville P. Ulmer is an academic researcher from Northwestern University. The author has contributed to research in topics: Galaxy & Galaxy cluster. The author has an hindex of 39, co-authored 290 publications receiving 5564 citations. Previous affiliations of Melville P. Ulmer include National Radio Astronomy Observatory & Association of Universities for Research in Astronomy.


Papers
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Journal ArticleDOI
TL;DR: In this paper, the luminosity function (LF) of galaxies in the core of the Coma cluster was determined, assuming H_0=75 km/s/Mpc, a magnitude regime previously explored only in the Local Group.
Abstract: We determine the luminosity function (LF) of galaxies in the core of the Coma cluster for M_R<=-11.4 (assuming H_0=75 km/s/Mpc), a magnitude regime previously explored only in the Local Group. Objects are counted in a deep CCD image of Coma having RMS noise of 27.7 R mag~arcsec$^{-2}$. A correction for objects in the foreground or background of the Coma cluster---and the uncertainty in this correction---are determined from images of five other high-latitude fields, carefully matched to the Coma image in both resolution and noise level. Accurate counts of Coma cluster members are obtained as faint as R=25.5, or M_R=-9.4. The LF for galaxies is well fit by a power law dN/dL\propto L^\alpha, with \alpha=-1.42\pm0.05, over the range -19.4

236 citations

Journal ArticleDOI
TL;DR: The Bright SHARC Survey as discussed by the authors is a large-scale search for serendipitously detected extended X-ray sources in 460 deep ROSAT PSPC pointings and has yielded 374 extended sources with a redshift range from 0.0696 to 0.83 and a luminosity range of 0.3e44 erg/s.
Abstract: We present the Bright SHARC (Serendipitous High-Redshift Archival ROSAT Cluster) Survey, which is an objective search for serendipitously detected extended X-ray sources in 460 deep ROSAT PSPC pointings. The Bright SHARC Survey covers an area of 178.6 sq.deg and has yielded 374 extended sources. We discuss the X-ray data reduction, the candidate selection and present results from our on-going optical follow-up campaign. The optical follow-up concentrates on the brightest 94 of the 374 extended sources and is now 97% complete. We have identified thirty-seven clusters of galaxies, for which we present redshifts and luminosities. The clusters span a redshift range of 0.0696

172 citations

Journal ArticleDOI
TL;DR: The Bright SHARC Survey as discussed by the authors was the first large-scale survey of high-Redshift archived ROSAT pointings and has yielded 374 extended sources with a redshift range from 0.0696 to 0.83 and a luminosity range of 0.5-2.0 keV.
Abstract: We present the Bright SHARC (Serendipitous High-Redshift Archival ROSAT Cluster) Survey, which is an objective search for serendipitously detected extended X-ray sources in 460 deep ROSAT PSPC pointings. The Bright SHARC Survey covers an area of 178.6 deg2 and has yielded 374 extended sources. We discuss the X-ray data reduction, the candidate selection and present results from our on-going optical follow-up campaign. The optical follow-up concentrates on the brightest 94 of the 374 extended sources and is now 97% complete. We have identified 37 clusters of galaxies, for which we present redshifts and luminosities. The clusters span a redshift range of 0.0696< z < 0.83 and a luminosity range of 0.065< LX< 8.31044 ergs s-1 [0.5-2.0 keV] (assuming H0=50 km s-1 Mpc-1 and q0=0.5). Twelve of the clusters have redshifts greater than z=0.3, eight of which are at luminosities brighter than LX=31044 ergs s-1. Seventeen of the 37 optically confirmed Bright SHARC clusters have not been listed in any previously published catalog. We also report the discovery of three candidate ``fossil groups'' of the kind proposed by Ponman et al. Based on data taken at the European Southern Observatory, Kitt Peak National Observatory, Cerro Tololo Inter-American Observatory, Canada-France-Hawaii, and Apache Point Observatory.

171 citations


Cited by
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Journal ArticleDOI
TL;DR: The authors compare the results of Eulerian hydrodynamic simulations of cluster formation against virial scaling relations between four bulk quantities: the cluster mass, the dark matter velocity dispersion, the gas temperature, and the cluster luminosity.
Abstract: We compare the results of Eulerian hydrodynamic simulations of cluster formation against virial scaling relations between four bulk quantities: the cluster mass, the dark matter velocity dispersion, the gas temperature, and the cluster luminosity. The comparison is made for a large number of clusters at a range of redshifts in three different cosmological models (cold plus hot dark matter, cold dark matter, and open cold dark matter). We find that the analytic formulae provide a good description of the relations between three of the four numerical quantities. The fourth (luminosity) also agrees once we introduce a procedure to correct for the fixed numerical resolution. We also compute the normalizations for the virial relations and compare extensively to the existing literature, finding remarkably good agreement. The Press-Schechter prescription is calibrated with the simulations, again finding results consistent with other authors. We also examine related issues such as the size of the scatter in the virial relations, the effect of metallicity with a fixed passband, and the structure of the halos. All of this is done in order to establish a firm groundwork for the use of clusters as cosmological probes. Implications for the models are briefly discussed.

2,018 citations

15 Mar 1979
TL;DR: In this article, the experimental estimation of parameters for models can be solved through use of the likelihood ratio test, with particular attention to photon counting experiments, and procedures presented solve a greater range of problems than those currently in use, yet are no more difficult to apply.
Abstract: Many problems in the experimental estimation of parameters for models can be solved through use of the likelihood ratio test. Applications of the likelihood ratio, with particular attention to photon counting experiments, are discussed. The procedures presented solve a greater range of problems than those currently in use, yet are no more difficult to apply. The procedures are proved analytically, and examples from current problems in astronomy are discussed.

1,748 citations

Journal ArticleDOI
TL;DR: In this paper, the structural and point defects caused by lattice and stacking mismatch with substrates are discussed. But even the best of the three binaries, InN, AIN and AIN as well as their ternary compounds, contain many structural defects, and these defects notably affect the electrical and optical properties of the host material.
Abstract: Gallium nitride (GaN) and its allied binaries InN and AIN as well as their ternary compounds have gained an unprecedented attention due to their wide-ranging applications encompassing green, blue, violet, and ultraviolet (UV) emitters and detectors (in photon ranges inaccessible by other semiconductors) and high-power amplifiers. However, even the best of the three binaries, GaN, contains many structural and point defects caused to a large extent by lattice and stacking mismatch with substrates. These defects notably affect the electrical and optical properties of the host material and can seriously degrade the performance and reliability of devices made based on these nitride semiconductors. Even though GaN broke the long-standing paradigm that high density of dislocations precludes acceptable device performance, point defects have taken the center stage as they exacerbate efforts to increase the efficiency of emitters, increase laser operation lifetime, and lead to anomalies in electronic devices. The p...

1,724 citations

Journal ArticleDOI
TL;DR: The authors compare the results of Eulerian hydrodynamic simulations of cluster formation against virial scaling relations between four bulk quantities: the cluster mass, the dark matter velocity dispersion, the gas temperature and the cluster luminosity.
Abstract: We compare the results of Eulerian hydrodynamic simulations of cluster formation against virial scaling relations between four bulk quantities: the cluster mass, the dark matter velocity dispersion, the gas temperature and the cluster luminosity. The comparison is made for a large number of clusters at a range of redshifts in three different cosmological models (CHDM, CDM and OCDM). We find that the analytic formulae provide a good description of the relations between three of the four numerical quantities. The fourth (luminosity) also agrees once we introduce a procedure to correct for the fixed numerical resolution. We also compute the normalizations for the virial relations and compare extensively to the existing literature, finding remarkably good agreement. The Press-Schechter prescription is calibrated with the simulations, again finding results consistent with other authors. We also examine related issues such as the size of the scatter in the virial relations, the effect of metallicity with a fixed pass-band, and the structure of the halos. All of this is done in order to establish a firm groundwork for the use of clusters as cosmological probes. Implications for the models are briefly discussed.

1,497 citations

Journal ArticleDOI
TL;DR: In this paper, a comprehensive analysis of the developments in ultraviolet (UV) detector technology is described and the current state of the art of different types of semiconductor UV detectors is presented.
Abstract: In this review article a comprehensive analysis of the developments in ultraviolet (UV) detector technology is described. At the beginning, the classification of UV detectors and general requirements imposed on these detectors are presented. Further considerations are restricted to modern semiconductor UV detectors, so the basic theory of photoconductive and photovoltaic detectors is presented in a uniform way convenient for various detector materials. Next, the current state of the art of different types of semiconductor UV detectors is presented. Hitherto, the semiconductor UV detectors have been mainly fabricated using Si. Industries such as the aerospace, automotive, petroleum, and others have continuously provided the impetus pushing the development of fringe technologies which are tolerant of increasingly high temperatures and hostile environments. As a result, the main efforts are currently directed to a new generation of UV detectors fabricated from wide band‐gap semiconductors the most promising ...

1,308 citations