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At least 1,171 records · Page 65

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NASA NTRS1982

Einstein Observatory solid state spectrometer observations of M87 and the Virgo cluster

X-ray observations of the galaxy M87 and of a region in the Virgo cluster displaced 7 arcmin from the center of M87 are reported. X-ray spectra were obtained at these two locations with the Solid State Spectrometer onboard the Einstein Observatory. Emission lines were observed in both locations, indicating the presence of heavy elements at abundances near solar. There is no strong abundance gradient, within the errors. A temperature gradient has been detected: T increases from about 1.4 keV at the position of M87 to about 3.35 keV 7 arcmin away. There is lower temperature thermal emission at the center of M87 with T about 0.6 keV, consistent with models for cooling flows in this cluster. A mass infall rate of nearly 20 solar masses/yr has been obtained. In addition to the thermal emission, a power-law component has been detected in the spectrum of M87, consistent with that observed by HEAO 1, indicating that this component probably originates in the galaxy itself. Comparison of the results with those of other observers and with theoretical models for this source indicates the presence of intracluster gas having density near 1/1000 per cu cm and temperature of about 30,000,000 K.

Lea, S. M.↗

NASA NTRS1983

Galaxy clusters with multiple components. II - Abell 115

Abell 115 is a galaxy cluster with two large enhancements in X-ray surface brightness. A map of the galaxy distribution over an extended region reveals the presence of three primary clumps of galaxies. Two of these correspond to the peaks in the X-ray surface brightness. A third clump, 7 arcmin to the east of the pair, has no X-ray emission detected by the Einstein Observatory. Redshifts are measured for 29 galaxies in the region; 10 are certainly members of foreground groups. A115, at z approximately 0.2, is the highest redshift cluster for which any extensive attempt has been made to study the system dynamics.

Beers, T. C.↗

NASA NTRS1983

Discovery of a nitrogen-rich UV-bright star in the globular cluster M5

Observations of a UV bright source in the globular cluster M5 using instrumentation on the Black Brant rocket are reported. Imagery was obtained by two cameras operating at 1540 A and 2360 A and bandpasses of 350 A and 880 A. The instruments are prototypes for cameras to be flown with the Spacelab. The UV-emitting object in the cluster was located off-center. Comparison of the data with data from the IUE for short-wavelength radiation indicated a temperature in the range 25,000-50,000 K, with a dereddened flux for the continuum near 1550 A of 4.2 x 10 to the -13th ergs/sq cm per sec per A. The object is concluded to be a post-AGB star with an envelope which has experienced CNO processing.

Bohlin, R. C.↗

NASA NTRS1983

X-ray, optical, and radio observations of the blue galaxy Butcher-Oemler 6 in the 3C 295 cluster

The nature of the blue members of distant, condensed clusters of galaxies are investigated through X ray, optical, and radio observations of the brightest such object in the 3C 295 cluster. The X ray luminosity and the optical emission line spectrum show that this galaxy is a Seyfert, in contrast to the original suggestion that the blue galaxies are rapidly evolving spirals. The observations yield an X ray luminosity of 3.4 x 10 to the 44th ergs/sec (0.5-4.5 keV), strong optical emission lines of Mg II and forbidden O II at a redshift of 0.473, and an upper limit to the radio luminosity at 20 cm of 7.0 x 10 to the 24th W/Hz. Compared to other Seyfert galaxies, this object appears relatively X ray luminous, shows an average Mg II/X ray flux ratio, and is relatively weak in H-beta emission.

Lavery, R. J.↗

NASA NTRS1983

Properties of young clusters near reflection nebulae

Near infrared observations in the reflection nebulae NGC 703, 2023, and 2068 are used to study clusters of young stars found associated with these nebulae. At least 30 percent to 60 percent of these stars are pre-main sequence objects, as indicated by their infrared excesses, hydrogen line emission, or irregular variability. The spatial distributions and observed luminosity functions of these young open clusters are derived, and the inferred mass function and star formation efficiencies are discussed. Previously announced in STAR as N83-25628

Sellgren, K.↗

NASA NTRS1984

Studies of X-ray clusters of galaxies/intergalactic plasmas

Intergalactic plasmas were investigated from both an observational and theoretical point of view. A multiobject spectrometer, the MX spectrograph was used to obtain detailed dynamical information on clusters of galaxies; this information was then compared with X ray emission from hot gas in these clusters. Several spectra of galaxies are presented, and data reduction of the spectra was discussed. The existence of quasar winds in Seyfert galaxies and the interaction between such a wind and the interstellar medium also were considered.

Scott, J. S.↗

NASA NTRS1984

Theoretical research program to predict the properties of molecules and clusters containing transition metal atoms

The primary focus of this research has been the theoretical study of transition metal (TM) chemistry. A major goal of this work is to provide reliable information about the interaction of H atoms with iron metal. This information is needed to understand the effect of H atoms on the processes of embrittlement and crack propagation in iron. The method in the iron hydrogen studies is the cluster method in which the bulk metal is modelled by a finite number of iron atoms. There are several difficulties in the application of this approach to the hydrogen iron system. First the nature of TM-TM and TM-H bonding for even diatomic molecules was not well understood when these studies were started. Secondly relatively large iron clusters are needed to provide reasonable results.

Walch, S.↗

NASA NTRS1984

The influence of containerless undercooling and rapid solid-state quenching on the superconductive and magnetic properties of some clustering alloy systems

The properties of clustering alloy systems and the manner in which they are influenced by rapid quenching from a containerless undercooled melt are discussed. It was postulated that rapid quenching under such conditions would result in highly disordered metastable alloys, and furthermore, that alloys in such conditions would possess physical properties characteristically different from those of alloys in the annealed equilibrium state. The scope of the program is essentially to gauge the influence of containerless undercooling on the submicrostructure of clustering-type alloys, using certain physical properties as diagnostic tools. Microstructures and macrostructures were to be examined using optical- and scanning-electron microscopy.

Collings, E. W.↗

NASA NTRS1983

Temperature and elemental abundances in the Abell cluster A 576 derived from X-ray observations

Results of Einstein solid state spectrometer observations of the central region of Abell 576 combined with HEAO 1 spectra of the total cluster are given. Line emission was detected due to Fe, Si, and S from a hot plasma in the central region. The temperature of the total cluster spectrum may be in conflict with the central temperature. This difference can be explained either if cooling takes place in the center, or if part of the measured emission is due to individual galaxies. If the X-ray emission comes from the intergalactic gas only, there is some difficulty in producing all the silicon observed in the galaxies of A 576.

Rothenflug, R.↗

NASA NTRS1983

Numerical experiments on galaxy clustering

A study of the way observable clustering depends on expansion history is reported. Observable shapes that result from evolving otherwise identical systems are intercompared to show differences due to different expansion histories. Four cases are compared: nonexpanding, Omega = 1, and two open universes with 0.10 and 0.03 as final values of Omega. There is remarkably little diffrence in observable forms for the expanding cases. The 0.03 universe expanded by a factor 500 during the experiment. This study is an example of the way numerical experiments can be used in studies of galaxy clustering.

Miller, R. H.↗

NASA NTRS1984

The X-ray luminosity function of Abell clusters at a redshift of 0.25

The X-ray luminosity function of Abell clusters was determined from a sample with mean redshift 0.25. This luminosity function is the same within the errors to that at low redshift. The time scale for changes in the X-ray luminosity of clusters of galaxies is thus greater than 4.0 billion years.

Henry, J. P.↗

NASA NTRS1984

The evolution of highly compact binary stellar systems in globular clusters

A highly compact binary represents a system which is composed of a collapsed object (degenerate dwarf, neutron star, or black hole) in orbit with a low-mass (equal to or less than 0.5 solar mass) secondary star. Matter may be transferred from the secondary to the collapsed star due to the decay of the orbit resulting from the emission of gravitational radiation. The present investigation has the objective to study quantitatively the evolution of highly compact binaries in globular cluster cores, subject to the interplay of gravitational radiation and collisions with field stars. The investigation is exploratory in nature. The numerical methods employed are based on the techniques developed by Rappaport et al. (1982). It is found that occasional close encounters with field stars strongly dominate the evolution of highly compact binaries in dense globular cluster cores. Attention is given to the applicability of the findings to observations of X-ray sources and cataclysmic variables.

Krolik, J. H.↗

NASA NTRS1985

A cluster analysis method for identification of subpopulations of cells in flow cytometric list-mode arrays

A specialized program was developed for flow cytometric list-mode data using an heirarchical tree method for identifying and enumerating individual subpopulations, the method of principal components for a two-dimensional display of 6-parameter data array, and a standard sorting algorithm for characterizing subpopulations. The program was tested against a published data set subjected to cluster analysis and experimental data sets from controlled flow cytometry experiments using a Coulter Electronics EPICS V Cell Sorter. A version of the program in compiled BASIC is usable on a 16-bit microcomputer with the MS-DOS operating system. It is specialized for 6 parameters and up to 20,000 cells. Its two-dimensional display of Euclidean distances reveals clusters clearly, as does its 1-dimensional display. The identified subpopulations can, in suitable experiments, be related to functional subpopulations of cells.

Li, Z. K.↗

NASA NTRS1985

Clusters and cycles in the cosmic ray age distributions of meteorites

Statistically significant clusters in the cosmic ray exposure age distributions of some groups of iron and stone meteorites were observed, suggesting epochs of enhanced collision and breakups. Fourier analyses of the age distributions of chondrites reveal no significant periods, nor does the same analysis when applied to iron meteorite clusters.

Woodard, M. F.↗

NASA NTRS1984

The radial X-ray brightness profile of the Coma cluster

Radial brightness profiles of the Coma cluster of galaxies in the 0.15-4.0 keV X-ray band are presented, along both major and minor axes, from data obtained with the Einstein Observatory imaging proportional counter. These are compared to various theoretical brightness distributions predicted by Strimpel and Binney (1979), after the predictions have been modified to take into account the varying energy response and finite spatial resolution of the instrument. The observed profiles are closest to the isothermal oblate model of Strimpel and Binney (although there are some systematic differences), and may therefore lend support to 'pancake' theories of cluster origin. Possible sources for the systematic differences are discussed. The present study also suggests how improved modeling could make possible a more definitive oblate-versus-prolate test, even in the absence of additional data.

Chanan, G. A.↗

NASA NTRS1984

The ultraviolet spectra of the O and B stars in the young galactic cluster NGC 6530

The UV spectra between 1200 and 3000 A of stars in the young galactic cluster NGC 6530 and the surrounding association are studied. From the UBV colors and empirical as well as theoretical calibrations, the T(eff) and L for those stars which follow a sequence in the H-R diagram corresponding to the main sequence are determined. From a comparison with theoretical evolutionary tracks, the age of the cluster is estimated to be 5 + or - 2 x 10 to the 6th yr, with a very small scatter for the different stars. The UV extinction is determined for the stars from a comparison of theoretical model energy distributions for the stellar T(eff)s and the observed energy distributions. The stellar wind lines are studied, and strong stellar winds are found for bolometric magnetidues less than -8.

Boehm-Vitense, E.↗

NASA NTRS1985

Images in the rocket ultraviolet - The initial helium abundance and distance modulus of the globular cluster M5 from photometry of horizontal-branch stars

A natural laboratory for the study of postmain-sequence evolution of low-mass (less than one solar mass) metal-poor stars is provided by globular clusters. These clusters are, therefore, a critical aid for developing an understanding of advanced stages of stellar evolution and of the chemical evolution of the Galaxy. Bohlin et al. (1983) have described a study of the postasymptotic branch star near the center of M5. The present investigation is concerned with the fainter horizontal-branch stars. The observations were made with the aid of a rocket-borne 38 cm f/9.0 Ritchey-Chretien telescope. Attention is given to payload and flight data, preflight bandpass calibration, the reduction of flight data, star selection, position measurement, photometry, the minimum observed horizontal-branch mass and inferences on mass loss, and individual UV-bright stars.

Bohlin, R. C.↗

NASA NTRS1985

The changes in small metal cluster size with adsorption Be13Xn, X = H, O, S, Cl and F

The Be-Be and Be-adsorbate distances are optimized for small Be13Xn clusters,s assuming only two independent degrees of freedom. Results for chemisorption into the three-fold hollows are quite similar to those found for small metal clusters on supports. It is predicted that Cl and F will have the same effect on the metal-metal bond lengths, and so will O and S.

Bauschlicher, C. W., Jr.↗